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docs/2025-06-18/learn/versioning Changed · +5 / -5 lines
from line 3
33The Model Context Protocol uses string-based version identifiers following the format
44`YYYY-MM-DD`, to indicate the last date backwards incompatible changes were made.
55
6<Info>
7 The protocol version will *not* be incremented when the
8 protocol is updated, as long as the changes maintain backwards compatibility. This allows
9 for incremental improvements while preserving interoperability.
10</Info>
6> [!NOTE]
7>
8> The protocol version will *not* be incremented when the
9> protocol is updated, as long as the changes maintain backwards compatibility. This allows
10> for incremental improvements while preserving interoperability.
1111
1212## Revisions
1313
docs/2025-06-18/sdk Changed · +16 / -18 lines
from line 8
88
99| SDK | Repository | Tier |
1010| :- | :- | -: |
11| <Icon icon="square-js" size={24} /> [TypeScript](https://ts.sdk.modelcontextprotocol.io) | [modelcontextprotocol/typescript-sdk](https://github.com/modelcontextprotocol/typescript-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
12| <Icon icon="python" size={24} /> [Python](https://py.sdk.modelcontextprotocol.io) | [modelcontextprotocol/python-sdk](https://github.com/modelcontextprotocol/python-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
13| <Icon icon="square-c" size={24} /> [C#](https://csharp.sdk.modelcontextprotocol.io) | [modelcontextprotocol/csharp-sdk](https://github.com/modelcontextprotocol/csharp-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
14| <Icon icon="golang" size={24} /> [Go](https://go.sdk.modelcontextprotocol.io) | [modelcontextprotocol/go-sdk](https://github.com/modelcontextprotocol/go-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
15| <Icon icon="java" size={24} /> [Java](https://java.sdk.modelcontextprotocol.io) | [modelcontextprotocol/java-sdk](https://github.com/modelcontextprotocol/java-sdk) | <Badge color="purple" shape="pill">Tier 2</Badge> |
16| <Icon icon="rust" size={24} /> [Rust](https://rust.sdk.modelcontextprotocol.io) | [modelcontextprotocol/rust-sdk](https://github.com/modelcontextprotocol/rust-sdk) | <Badge color="purple" shape="pill">Tier 2</Badge> |
17| <Icon icon="swift" size={24} /> Swift | [modelcontextprotocol/swift-sdk](https://github.com/modelcontextprotocol/swift-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
18| <Icon icon="gem" size={24} /> [Ruby](https://ruby.sdk.modelcontextprotocol.io) | [modelcontextprotocol/ruby-sdk](https://github.com/modelcontextprotocol/ruby-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
19| <Icon icon="php" size={24} /> [PHP](https://php.sdk.modelcontextprotocol.io) | [modelcontextprotocol/php-sdk](https://github.com/modelcontextprotocol/php-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
20| <Icon icon="square-k" size={24} /> [Kotlin](https://kotlin.sdk.modelcontextprotocol.io) | [modelcontextprotocol/kotlin-sdk](https://github.com/modelcontextprotocol/kotlin-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
11| [TypeScript](https://ts.sdk.modelcontextprotocol.io) | [modelcontextprotocol/typescript-sdk](https://github.com/modelcontextprotocol/typescript-sdk) | Tier 1 |
12| [Python](https://py.sdk.modelcontextprotocol.io) | [modelcontextprotocol/python-sdk](https://github.com/modelcontextprotocol/python-sdk) | Tier 1 |
13| [C#](https://csharp.sdk.modelcontextprotocol.io) | [modelcontextprotocol/csharp-sdk](https://github.com/modelcontextprotocol/csharp-sdk) | Tier 1 |
14| [Go](https://go.sdk.modelcontextprotocol.io) | [modelcontextprotocol/go-sdk](https://github.com/modelcontextprotocol/go-sdk) | Tier 1 |
15| [Java](https://java.sdk.modelcontextprotocol.io) | [modelcontextprotocol/java-sdk](https://github.com/modelcontextprotocol/java-sdk) | Tier 2 |
16| [Rust](https://rust.sdk.modelcontextprotocol.io) | [modelcontextprotocol/rust-sdk](https://github.com/modelcontextprotocol/rust-sdk) | Tier 2 |
17| Swift | [modelcontextprotocol/swift-sdk](https://github.com/modelcontextprotocol/swift-sdk) | Tier 3 |
18| [Ruby](https://ruby.sdk.modelcontextprotocol.io) | [modelcontextprotocol/ruby-sdk](https://github.com/modelcontextprotocol/ruby-sdk) | Tier 3 |
19| [PHP](https://php.sdk.modelcontextprotocol.io) | [modelcontextprotocol/php-sdk](https://github.com/modelcontextprotocol/php-sdk) | Tier 3 |
20| [Kotlin](https://kotlin.sdk.modelcontextprotocol.io) | [modelcontextprotocol/kotlin-sdk](https://github.com/modelcontextprotocol/kotlin-sdk) | Tier 3 |
2121
2222See [SDK Tiering System](/community/sdk-tiers) for details on what each tier means.
2323
from line 36
3636
3737Ready to start building with MCP? Choose your path:
3838
39<CardGroup cols={2}>
40 <Card title="Build a Server" icon="server" href="/docs/2025-06-18/develop/build-server">
41 Learn how to create your first MCP server
42 </Card>
39> **[Build a Server](/docs/2025-06-18/develop/build-server)**
40>
41> Learn how to create your first MCP server
4342
44 <Card title="Build a Client" icon="computer" href="/docs/2025-06-18/develop/build-client">
45 Create applications that connect to MCP servers
46 </Card>
47</CardGroup>
43> **[Build a Client](/docs/2025-06-18/develop/build-client)**
44>
45> Create applications that connect to MCP servers
4846
docs/2025-06-18/tools/debugging Changed · +46 / -54 lines
from line 32
3232logged to stderr (standard error) will be captured by the host application
3333automatically.
3434
35<Warning>
36 Local MCP servers should not log messages to stdout (standard out), as this
37 will interfere with protocol operation.
38</Warning>
35> [!WARNING]
36>
37> Local MCP servers should not log messages to stdout (standard out), as this
38> will interfere with protocol operation.
3939
4040For servers using the
4141[Streamable HTTP transport](/specification/2025-06-18/basic/transports#streamable-http),
from line 48
4848For all [transports](/specification/2025-06-18/basic/transports), you can also
4949provide logging to the client by sending a log message notification:
5050
51<CodeGroup>
52 ```python Python theme={null}
53 @server.tool()
54 async def my_tool(ctx: Context) -> str:
55 await ctx.session.send_log_message(
56 level="info",
57 data="Server started successfully",
58 )
59 return "done"
60 ```
51```python Python theme={null}
52@server.tool()
53async def my_tool(ctx: Context) -> str:
54 await ctx.session.send_log_message(
55 level="info",
56 data="Server started successfully",
57 )
58 return "done"
59```
6160
62 ```typescript TypeScript theme={null}
63 await server.sendLoggingMessage({
64 level: "info",
65 data: "Server started successfully",
66 });
67 ```
68</CodeGroup>
61```typescript TypeScript theme={null}
62await server.sendLoggingMessage({
63 level: "info",
64 data: "Server started successfully",
65});
66```
6967
7068MCP defines eight
7169[RFC 5424 severity levels](/specification/2025-06-18/server/utilities/logging#log-levels)
from line 189
191189hover over the **Connectors** menu to see connected servers and available
192190tools.
193191
194<img src="https://mintcdn.com/mcp/zNouQwo2h8cbxlDS/images/available-mcp-tools.png?fit=max&auto=format&n=zNouQwo2h8cbxlDS&q=85&s=e2ace1ac88895a5fe30ebd8d01456bc3" alt="Available MCP tools" width="437" height="244" data-path="images/available-mcp-tools.png" />
192
195193
196194### Viewing logs
197195
from line 198
200198* macOS: `~/Library/Logs/Claude`
201199* Windows: `%APPDATA%\Claude\logs`
202200
203<CodeGroup>
204 ```bash macOS theme={null}
205 tail -n 20 -F ~/Library/Logs/Claude/mcp*.log
206 ```
201```bash macOS theme={null}
202tail -n 20 -F ~/Library/Logs/Claude/mcp*.log
203```
207204
208 ```powershell Windows theme={null}
209 type "$env:AppData\Claude\logs\mcp*.log"
210 ```
211</CodeGroup>
205```powershell Windows theme={null}
206type "$env:AppData\Claude\logs\mcp*.log"
207```
212208
213209The logs capture:
214210
from line 220
224220
2252211. Create a `developer_settings.json` file with `allowDevTools` set to true:
226222
227<CodeGroup>
228 ```bash macOS theme={null}
229 echo '{"allowDevTools": true}' > ~/Library/Application\ Support/Claude/developer_settings.json
230 ```
223```bash macOS theme={null}
224echo '{"allowDevTools": true}' > ~/Library/Application\ Support/Claude/developer_settings.json
225```
231226
232 ```powershell Windows theme={null}
233 '{"allowDevTools": true}' | Set-Content "$env:AppData\Claude\developer_settings.json"
234 ```
235</CodeGroup>
227```powershell Windows theme={null}
228'{"allowDevTools": true}' | Set-Content "$env:AppData\Claude\developer_settings.json"
229```
236230
2372312. Open DevTools: `Command-Option-I` (macOS) or `Ctrl+Alt+I` (Windows)
238232
from line 327
333327
334328## Next steps
335329
336<CardGroup cols={2}>
337 <Card title="MCP Inspector" icon="magnifying-glass" href="/docs/2025-06-18/tools/inspector">
338 Learn to use the MCP Inspector
339 </Card>
330> **[MCP Inspector](/docs/2025-06-18/tools/inspector)**
331>
332> Learn to use the MCP Inspector
340333
341 <Card title="Build an MCP server" icon="code" href="/docs/2025-06-18/develop/build-server">
342 Walk through building a server from scratch
343 </Card>
334> **[Build an MCP server](/docs/2025-06-18/develop/build-server)**
335>
336> Walk through building a server from scratch
344337
345 <Card title="Connect local servers" icon="plug" href="/docs/2025-06-18/develop/connect-local-servers">
346 Full claude\_desktop\_config.json reference and troubleshooting
347 </Card>
348</CardGroup>
338> **[Connect local servers](/docs/2025-06-18/develop/connect-local-servers)**
339>
340> Full claude\_desktop\_config.json reference and troubleshooting
349341
docs/2025-06-18/tools/inspector Changed · +36 / -44 lines
from line 22
2222
2323A common way to start server packages from [npm](https://npmjs.com) or [PyPI](https://pypi.org).
2424
25<Tabs>
26 <Tab title="npm package">
27 ```bash theme={null}
28 npx -y @modelcontextprotocol/inspector npx <package-name> <args>
29 # For example
30 npx -y @modelcontextprotocol/inspector npx @modelcontextprotocol/server-filesystem /Users/username/Desktop
31 ```
32 </Tab>
25**npm package**
3326
34 <Tab title="PyPI package">
35 ```bash theme={null}
36 npx @modelcontextprotocol/inspector uvx <package-name> <args>
37 # For example
38 npx @modelcontextprotocol/inspector uvx mcp-server-git --repository ~/code/mcp/servers.git
39 ```
40 </Tab>
41</Tabs>
27```bash theme={null}
28npx -y @modelcontextprotocol/inspector npx <package-name> <args>
29# For example
30npx -y @modelcontextprotocol/inspector npx @modelcontextprotocol/server-filesystem /Users/username/Desktop
31```
4232
33**PyPI package**
34
35```bash theme={null}
36npx @modelcontextprotocol/inspector uvx <package-name> <args>
37# For example
38npx @modelcontextprotocol/inspector uvx mcp-server-git --repository ~/code/mcp/servers.git
39```
40
4341#### Inspecting locally developed servers
4442
4543To inspect servers locally developed or downloaded as a repository, the most common
4644way is:
4745
48<Tabs>
49 <Tab title="TypeScript">
50 ```bash theme={null}
51 npx @modelcontextprotocol/inspector node path/to/server/index.js args...
52 ```
53 </Tab>
46**TypeScript**
5447
55 <Tab title="Python">
56 ```bash theme={null}
57 npx @modelcontextprotocol/inspector \
58 uv \
59 --directory path/to/server \
60 run \
61 package-name \
62 args...
63 ```
64 </Tab>
65</Tabs>
48```bash theme={null}
49npx @modelcontextprotocol/inspector node path/to/server/index.js args...
50```
6651
52**Python**
53
54```bash theme={null}
55npx @modelcontextprotocol/inspector \
56 uv \
57 --directory path/to/server \
58 run \
59 package-name \
60 args...
61```
62
6763Please carefully read any attached README for the most accurate instructions.
6864
6965## Feature overview
7066
71<Frame caption="The MCP Inspector interface">
72 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/mcp-inspector.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=83b12e2a457c96ef4ad17c7357236290" width="2888" height="1761" data-path="images/mcp-inspector.png" />
73</Frame>
67
7468
7569The Inspector provides several features for interacting with your MCP server:
7670
from line 123
129123
130124## Next steps
131125
132<CardGroup cols={2}>
133 <Card title="Inspector Repository" icon="github" href="https://github.com/modelcontextprotocol/inspector">
134 Check out the MCP Inspector source code
135 </Card>
126> **[Inspector Repository](https://github.com/modelcontextprotocol/inspector)**
127>
128> Check out the MCP Inspector source code
136129
137 <Card title="Debugging Guide" icon="bug" href="/docs/2025-06-18/tools/debugging">
138 Learn about broader debugging strategies
139 </Card>
140</CardGroup>
130> **[Debugging Guide](/docs/2025-06-18/tools/debugging)**
131>
132> Learn about broader debugging strategies
141133
docs/2025-06-18/tutorials/security/authorization Changed · +841 / -861 lines
The two sides of this change are more than 400 edits apart, too far apart to line up, so this is the differ's own diff of it and the words inside a line are not marked.
from line 16
1616* You're building for enterprise environments with strict access controls
1717* You want to implement rate limiting or usage tracking per user
1818
19<Tip>
20 **Authorization for Local MCP Servers**
21
22 For MCP servers using the [STDIO transport](/specification/2025-06-18/basic/transports#stdio), you can use environment-based credentials or credentials provided by third-party libraries embedded directly in the MCP server instead. Because a STDIO-built MCP server runs locally, it has access to a range of flexible options when it comes to acquiring user credentials that may or may not rely on in-browser authentication and authorization flows.
23
24 OAuth flows, in turn, are designed for HTTP-based transports where the MCP server is remotely-hosted and the client uses OAuth to establish that a user is authorized to access said remote server.
25</Tip>
19> [!TIP]
20>
21> **Authorization for Local MCP Servers**
22>
23> For MCP servers using the [STDIO transport](/specification/2025-06-18/basic/transports#stdio), you can use environment-based credentials or credentials provided by third-party libraries embedded directly in the MCP server instead. Because a STDIO-built MCP server runs locally, it has access to a range of flexible options when it comes to acquiring user credentials that may or may not rely on in-browser authentication and authorization flows.
24>
25> OAuth flows, in turn, are designed for HTTP-based transports where the MCP server is remotely-hosted and the client uses OAuth to establish that a user is authorized to access said remote server.
2626
2727## The Authorization Flow: Step by Step
2828
2929Let's walk through what happens when a client wants to connect to your protected MCP server:
3030
31<Steps>
32 <Step title="Initial Handshake">
33 When your MCP client first tries to connect, your server responds with a `401 Unauthorized` and tells the client where to find authorization information, captured in a [Protected Resource Metadata (PRM) document](https://datatracker.ietf.org/doc/html/rfc9728). The document is hosted by the MCP server, follows a predictable path pattern, and is provided to the client in the `resource_metadata` parameter within the `WWW-Authenticate` header.
34
35 ```http theme={null}
36 HTTP/1.1 401 Unauthorized
37 WWW-Authenticate: Bearer realm="mcp",
38 resource_metadata="https://your-server.com/.well-known/oauth-protected-resource"
39 ```
40
41 This tells the client that authorization is required for the MCP server and where to get the necessary information to kickstart the authorization flow.
42 </Step>
43
44 <Step title="Protected Resource Metadata Discovery">
45 With the URI pointer to the PRM document, the client will fetch the metadata to learn about the authorization server, supported scopes, and other resource information. The data is typically encapsulated in a JSON blob, similar to the one below.
46
47 ```json theme={null}
48 {
49 "resource": "https://your-server.com/mcp",
50 "authorization_servers": ["https://auth.your-server.com"],
51 "scopes_supported": ["mcp:tools", "mcp:resources"]
52 }
53 ```
54
55 You can see a more comprehensive example in [RFC 9728 Section 3.2](https://datatracker.ietf.org/doc/html/rfc9728#name-protected-resource-metadata-r).
56 </Step>
57
58 <Step title="Authorization Server Discovery">
59 Next, the client discovers what the authorization server can do by fetching its metadata. If the PRM document lists more than one authorization server, the client can decide which one to use.
60
61 With an authorization server selected, the client will then construct a standard metadata URI and issue a request to the [OpenID Connect (OIDC) Discovery](https://openid.net/specs/openid-connect-discovery-1_0.html) or [OAuth 2.0 Auth Server Metadata](https://datatracker.ietf.org/doc/html/rfc8414) endpoints (depending on authorization server support)
62 and retrieve another set of metadata properties that will allow it to know the endpoints it needs to complete the authorization flow.
63
64 ```json theme={null}
65 {
66 "issuer": "https://auth.your-server.com",
67 "authorization_endpoint": "https://auth.your-server.com/authorize",
68 "token_endpoint": "https://auth.your-server.com/token",
69 "registration_endpoint": "https://auth.your-server.com/register"
70 }
71 ```
72 </Step>
73
74 <Step title="Client Registration">
75 With all the metadata out of the way, the client now needs to make sure that it's registered with the authorization server. This can be done in two ways.
76
77 First, the client can be **pre-registered** with a given authorization server, in which case it can have embedded client registration information that it uses to complete the authorization flow.
78
79 Alternatively, the client can use **Dynamic Client Registration** (DCR) to dynamically register itself with the authorization server. The latter scenario requires the authorization server to support DCR. If the authorization server does support DCR, the client will send a request to the `registration_endpoint` with its information:
80
81 ```json theme={null}
82 {
83 "client_name": "My MCP Client",
84 "redirect_uris": ["http://localhost:3000/callback"],
85 "grant_types": ["authorization_code", "refresh_token"],
86 "response_types": ["code"]
87 }
88 ```
89
90 If the registration succeeds, the authorization server will return a JSON blob with client registration information.
91
92 <Tip>
93 **No DCR or Pre-Registration**
94
95 In case an MCP client connects to an MCP server that doesn't use an authorization server that supports DCR and the client is not pre-registered with said authorization server, it's the responsibility of the client developer to provide an affordance for the end-user to enter client information manually.
96 </Tip>
97 </Step>
98
99 <Step title="User Authorization">
100 The client will now need to open a browser to the `/authorize` endpoint, where the user can log in and grant the required permissions. The authorization server will then redirect back to the client with an authorization code that the client exchanges for tokens:
101
102 ```json theme={null}
103 {
104 "access_token": "eyJhbGciOiJSUzI1NiIs...",
105 "refresh_token": "def502...",
106 "token_type": "Bearer",
107 "expires_in": 3600
108 }
109 ```
110
111 The access token is what the client will use to authenticate requests to the MCP server. This step follows standard [OAuth 2.1 authorization code with PKCE](https://oauth.net/2/grant-types/authorization-code/) conventions.
112 </Step>
113
114 <Step title="Making Authenticated Requests">
115 Finally, the client can make requests to your MCP server using the access token embedded in the `Authorization` header:
116
117 ```http theme={null}
118 GET /mcp HTTP/1.1
119 Host: your-server.com
120 Authorization: Bearer eyJhbGciOiJSUzI1NiIs...
121 ```
122
123 The MCP server will need to validate the token and process the request if the token is valid and has the required permissions.
124 </Step>
125</Steps>
31**1. Initial Handshake**
32
33When your MCP client first tries to connect, your server responds with a `401 Unauthorized` and tells the client where to find authorization information, captured in a [Protected Resource Metadata (PRM) document](https://datatracker.ietf.org/doc/html/rfc9728). The document is hosted by the MCP server, follows a predictable path pattern, and is provided to the client in the `resource_metadata` parameter within the `WWW-Authenticate` header.
34
35```http theme={null}
36HTTP/1.1 401 Unauthorized
37WWW-Authenticate: Bearer realm="mcp",
38 resource_metadata="https://your-server.com/.well-known/oauth-protected-resource"
39```
40
41This tells the client that authorization is required for the MCP server and where to get the necessary information to kickstart the authorization flow.
42
43**2. Protected Resource Metadata Discovery**
44
45With the URI pointer to the PRM document, the client will fetch the metadata to learn about the authorization server, supported scopes, and other resource information. The data is typically encapsulated in a JSON blob, similar to the one below.
46
47```json theme={null}
48{
49 "resource": "https://your-server.com/mcp",
50 "authorization_servers": ["https://auth.your-server.com"],
51 "scopes_supported": ["mcp:tools", "mcp:resources"]
52}
53```
54
55You can see a more comprehensive example in [RFC 9728 Section 3.2](https://datatracker.ietf.org/doc/html/rfc9728#name-protected-resource-metadata-r).
56
57**3. Authorization Server Discovery**
58
59Next, the client discovers what the authorization server can do by fetching its metadata. If the PRM document lists more than one authorization server, the client can decide which one to use.
60
61With an authorization server selected, the client will then construct a standard metadata URI and issue a request to the [OpenID Connect (OIDC) Discovery](https://openid.net/specs/openid-connect-discovery-1_0.html) or [OAuth 2.0 Auth Server Metadata](https://datatracker.ietf.org/doc/html/rfc8414) endpoints (depending on authorization server support)
62and retrieve another set of metadata properties that will allow it to know the endpoints it needs to complete the authorization flow.
63
64```json theme={null}
65{
66 "issuer": "https://auth.your-server.com",
67 "authorization_endpoint": "https://auth.your-server.com/authorize",
68 "token_endpoint": "https://auth.your-server.com/token",
69 "registration_endpoint": "https://auth.your-server.com/register"
70}
71```
72
73**4. Client Registration**
74
75With all the metadata out of the way, the client now needs to make sure that it's registered with the authorization server. This can be done in two ways.
76
77First, the client can be **pre-registered** with a given authorization server, in which case it can have embedded client registration information that it uses to complete the authorization flow.
78
79Alternatively, the client can use **Dynamic Client Registration** (DCR) to dynamically register itself with the authorization server. The latter scenario requires the authorization server to support DCR. If the authorization server does support DCR, the client will send a request to the `registration_endpoint` with its information:
80
81```json theme={null}
82{
83 "client_name": "My MCP Client",
84 "redirect_uris": ["http://localhost:3000/callback"],
85 "grant_types": ["authorization_code", "refresh_token"],
86 "response_types": ["code"]
87}
88```
89
90If the registration succeeds, the authorization server will return a JSON blob with client registration information.
91
92> [!TIP]
93>
94> **No DCR or Pre-Registration**
95>
96> In case an MCP client connects to an MCP server that doesn't use an authorization server that supports DCR and the client is not pre-registered with said authorization server, it's the responsibility of the client developer to provide an affordance for the end-user to enter client information manually.
97
98**5. User Authorization**
99
100The client will now need to open a browser to the `/authorize` endpoint, where the user can log in and grant the required permissions. The authorization server will then redirect back to the client with an authorization code that the client exchanges for tokens:
101
102```json theme={null}
103{
104 "access_token": "eyJhbGciOiJSUzI1NiIs...",
105 "refresh_token": "def502...",
106 "token_type": "Bearer",
107 "expires_in": 3600
108}
109```
110
111The access token is what the client will use to authenticate requests to the MCP server. This step follows standard [OAuth 2.1 authorization code with PKCE](https://oauth.net/2/grant-types/authorization-code/) conventions.
112
113**6. Making Authenticated Requests**
114
115Finally, the client can make requests to your MCP server using the access token embedded in the `Authorization` header:
116
117```http theme={null}
118GET /mcp HTTP/1.1
119Host: your-server.com
120Authorization: Bearer eyJhbGciOiJSUzI1NiIs...
121```
122
123The MCP server will need to validate the token and process the request if the token is valid and has the required permissions.
126124
127125## Implementation Example
128126
from line 138
140138
141139This command will pull the Keycloak container image locally and bootstrap the basic configuration. It will run on port `8080` and have an `admin` user with `admin` password.
142140
143<Warning>
144 **Not for Production**
145
146 The configuration above may be suitable for testing and experimentation; however, you should never use it in production. Refer to the [Configuring Keycloak for production](https://www.keycloak.org/server/configuration-production) guide for additional details on how to deploy the authorization server for scenarios that require reliability, security, and high availability.
147</Warning>
141> [!WARNING]
142>
143> **Not for Production**
144>
145> The configuration above may be suitable for testing and experimentation; however, you should never use it in production. Refer to the [Configuring Keycloak for production](https://www.keycloak.org/server/configuration-production) guide for additional details on how to deploy the authorization server for scenarios that require reliability, security, and high availability.
148146
149147You will be able to access the Keycloak authorization server from your browser at `http://localhost:8080`.
150148
151<Frame>
152 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-browser.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=cba689d986e113cbe937d732ac0558b6" alt="Keycloak admin dashboard authentication dialog." width="1834" height="1450" data-path="images/tutorial-authorization/keycloak-browser.png" />
153</Frame>
149
154150
155151When running with the default configuration, Keycloak will already support many of the capabilities that we need for MCP servers, including Dynamic Client Registration. You can check this by looking at the OIDC configuration, available at:
156152
from line 158
162158
163159Go to **Client scopes** in the Keycloak dashboard and create a new `mcp:tools` scope. We will use this to access all of the tools on our MCP server.
164160
165<Frame>
166 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-scopes.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=3cd49dc2e070027609ae495751e0db58" alt="Configuring Keycloak scopes." width="1999" height="1710" data-path="images/tutorial-authorization/keycloak-scopes.png" />
167</Frame>
161
168162
169163After creating the scope, make sure that you assign its type to **Default** and have flipped the **Include in token scope** switch, as this will be needed for token validation.
170164
from line 166
172166
173167To do this, open your `mcp:tools` client scope and click on **Mappers**, followed by **Configure a new mapper**. Select **Audience**.
174168
175<Frame>
176 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/scope-add-audience.gif?s=6ea9cf20c397f4c79c491c2e39019272" alt="Configuring an audience for a token in Keycloak." width="1080" height="921" data-path="images/tutorial-authorization/scope-add-audience.gif" />
177</Frame>
169
178170
179171For **Name**, use `audience-config`. Add a value for **Included Custom Audience**, set to `http://localhost:3000`. This will be the URI of our test server.
180172
181<Warning>
182 **Not for Production**
183
184 The audience configuration above is meant for testing. For production scenarios, additional set-up and configuration will be required to ensure that audiences are properly constrained for issued tokens. Specifically, the audience needs to be based on the resource parameter passed from the client, not a fixed value.
185</Warning>
173> [!WARNING]
174>
175> **Not for Production**
176>
177> The audience configuration above is meant for testing. For production scenarios, additional set-up and configuration will be required to ensure that audiences are properly constrained for issued tokens. Specifically, the audience needs to be based on the resource parameter passed from the client, not a fixed value.
186178
187179Now, navigate to **Clients**, then **Client registration**, and then **Trusted Hosts**. Disable the **Client URIs Must Match** setting and add the hosts from which you're testing. You can get your current host IP by running the `ifconfig` command on Linux or macOS, or `ipconfig` on Windows. You can see the IP address you need to add by looking at the keycloak logs for a line that looks like `Failed to verify remote host : 192.168.215.1`. Check that the IP address is associated with your host. This may be for a bridge network depending on your docker setup.
188180
189<Frame>
190 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-client.gif?s=b5d40b36a5f1ea1e818821bb8ea77f6b" alt="Setting up client registration details in Keycloak." width="1199" height="1027" data-path="images/tutorial-authorization/keycloak-client.gif" />
191</Frame>
192
193<Warning>
194 **Getting the Host**
195
196 If you are running Keycloak from a container, you will also be able to see the host IP from the Terminal in the container logs.
197</Warning>
181
182
183> [!WARNING]
184>
185> **Getting the Host**
186>
187> If you are running Keycloak from a container, you will also be able to see the host IP from the Terminal in the container logs.
198188
199189Lastly, we need to register a new client that we can use with the **MCP server itself** to talk to Keycloak for things like [token introspection](https://oauth.net/2/token-introspection/). To do that:
200190
from line 198
208198
209199When you open the client details, go to **Credentials** and take note of the **Client Secret**.
210200
211<Frame>
212 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-client-auth.gif?s=7152c41a5746994fd399024bc4659e40" alt="Creating a new client in Keycloak." width="1200" height="1023" data-path="images/tutorial-authorization/keycloak-client-auth.gif" />
213</Frame>
214
215<Warning>
216 **Handling Secrets**
217
218 Never embed client credentials directly in your code. We recommend using environment variables or specialized solutions for secret storage.
219</Warning>
201
202
203> [!WARNING]
204>
205> **Handling Secrets**
206>
207> Never embed client credentials directly in your code. We recommend using environment variables or specialized solutions for secret storage.
220208
221209With Keycloak configured, every time the authorization flow is triggered, your MCP server will receive a token like this:
222210
from line 234
246234}.[Signature]
247235```
248236
249<Warning>
250 **Embedded Audience**
251
252 Notice the `aud` claim embedded in the token - it's currently set to be the URI of the test MCP server and it's inferred from the scope that we've previously configured. This will be important in our implementation to validate.
253</Warning>
237> [!WARNING]
238>
239> **Embedded Audience**
240>
241> Notice the `aud` claim embedded in the token - it's currently set to be the URI of the test MCP server and it's inferred from the scope that we've previously configured. This will be important in our implementation to validate.
254242
255243### MCP Server Setup
256244
from line 246
258246
259247For our testing purposes, we will create an extremely simple MCP server that exposes two tools - one for addition and another for multiplication. The server will require authorization to access these.
260248
261<Tabs>
262 <Tab title="TypeScript">
263 You can see the complete TypeScript project in the [sample repository](https://github.com/localden/min-ts-mcp-auth).
264
265 Prior to running the code below, ensure that you have a `.env` file with the following content:
266
267 ```env theme={null}
268 # Server host/port
269 HOST=localhost
270 PORT=3000
271
272 # Auth server location
273 AUTH_HOST=localhost
274 AUTH_PORT=8080
275 AUTH_REALM=master
276
277 # Keycloak OAuth client credentials
278 OAUTH_CLIENT_ID=<YOUR_SERVER_CLIENT_ID>
279 OAUTH_CLIENT_SECRET=<YOUR_SERVER_CLIENT_SECRET>
280 ```
281
282 `OAUTH_CLIENT_ID` and `OAUTH_CLIENT_SECRET` are associated with the MCP server client we created earlier.
283
284 In addition to implementing the MCP authorization specification, the server below also does token introspection via Keycloak to make sure that the token it receives from the client is valid. It also implements basic logging to allow you to easily diagnose any issues.
285
286 ```typescript theme={null}
287 import "dotenv/config";
288 import express from "express";
289 import { randomUUID } from "node:crypto";
290 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
291 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
292 import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js";
293 import { z } from "zod";
294 import cors from "cors";
295 import {
296 mcpAuthMetadataRouter,
297 getOAuthProtectedResourceMetadataUrl,
298 } from "@modelcontextprotocol/sdk/server/auth/router.js";
299 import { requireBearerAuth } from "@modelcontextprotocol/sdk/server/auth/middleware/bearerAuth.js";
300 import { OAuthMetadata } from "@modelcontextprotocol/sdk/shared/auth.js";
301 import { checkResourceAllowed } from "@modelcontextprotocol/sdk/shared/auth-utils.js";
302 const CONFIG = {
303 host: process.env.HOST || "localhost",
304 port: Number(process.env.PORT) || 3000,
305 auth: {
306 host: process.env.AUTH_HOST || process.env.HOST || "localhost",
307 port: Number(process.env.AUTH_PORT) || 8080,
308 realm: process.env.AUTH_REALM || "master",
309 clientId: process.env.OAUTH_CLIENT_ID || "mcp-server",
310 clientSecret: process.env.OAUTH_CLIENT_SECRET || "",
311 },
312 };
313
314 function createOAuthUrls() {
315 const authBaseUrl = new URL(
316 `http://${CONFIG.auth.host}:${CONFIG.auth.port}/realms/${CONFIG.auth.realm}/`,
249**TypeScript**
250
251You can see the complete TypeScript project in the [sample repository](https://github.com/localden/min-ts-mcp-auth).
252
253Prior to running the code below, ensure that you have a `.env` file with the following content:
254
255```env theme={null}
256# Server host/port
257HOST=localhost
258PORT=3000
259
260# Auth server location
261AUTH_HOST=localhost
262AUTH_PORT=8080
263AUTH_REALM=master
264
265# Keycloak OAuth client credentials
266OAUTH_CLIENT_ID=<YOUR_SERVER_CLIENT_ID>
267OAUTH_CLIENT_SECRET=<YOUR_SERVER_CLIENT_SECRET>
268```
269
270`OAUTH_CLIENT_ID` and `OAUTH_CLIENT_SECRET` are associated with the MCP server client we created earlier.
271
272In addition to implementing the MCP authorization specification, the server below also does token introspection via Keycloak to make sure that the token it receives from the client is valid. It also implements basic logging to allow you to easily diagnose any issues.
273
274```typescript theme={null}
275import "dotenv/config";
276import express from "express";
277import { randomUUID } from "node:crypto";
278import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
279import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
280import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js";
281import { z } from "zod";
282import cors from "cors";
283import {
284 mcpAuthMetadataRouter,
285 getOAuthProtectedResourceMetadataUrl,
286} from "@modelcontextprotocol/sdk/server/auth/router.js";
287import { requireBearerAuth } from "@modelcontextprotocol/sdk/server/auth/middleware/bearerAuth.js";
288import { OAuthMetadata } from "@modelcontextprotocol/sdk/shared/auth.js";
289import { checkResourceAllowed } from "@modelcontextprotocol/sdk/shared/auth-utils.js";
290const CONFIG = {
291 host: process.env.HOST || "localhost",
292 port: Number(process.env.PORT) || 3000,
293 auth: {
294 host: process.env.AUTH_HOST || process.env.HOST || "localhost",
295 port: Number(process.env.AUTH_PORT) || 8080,
296 realm: process.env.AUTH_REALM || "master",
297 clientId: process.env.OAUTH_CLIENT_ID || "mcp-server",
298 clientSecret: process.env.OAUTH_CLIENT_SECRET || "",
299 },
300};
301
302function createOAuthUrls() {
303 const authBaseUrl = new URL(
304 `http://${CONFIG.auth.host}:${CONFIG.auth.port}/realms/${CONFIG.auth.realm}/`,
305 );
306 return {
307 issuer: authBaseUrl.toString(),
308 introspection_endpoint: new URL(
309 "protocol/openid-connect/token/introspect",
310 authBaseUrl,
311 ).toString(),
312 authorization_endpoint: new URL(
313 "protocol/openid-connect/auth",
314 authBaseUrl,
315 ).toString(),
316 token_endpoint: new URL(
317 "protocol/openid-connect/token",
318 authBaseUrl,
319 ).toString(),
320 };
321}
322
323function createRequestLogger() {
324 return (req: any, res: any, next: any) => {
325 const start = Date.now();
326 res.on("finish", () => {
327 const ms = Date.now() - start;
328 console.log(
329 `${req.method} ${req.originalUrl} -> ${res.statusCode} ${ms}ms`,
317330 );
318 return {
319 issuer: authBaseUrl.toString(),
320 introspection_endpoint: new URL(
321 "protocol/openid-connect/token/introspect",
322 authBaseUrl,
323 ).toString(),
324 authorization_endpoint: new URL(
325 "protocol/openid-connect/auth",
326 authBaseUrl,
327 ).toString(),
328 token_endpoint: new URL(
329 "protocol/openid-connect/token",
330 authBaseUrl,
331 ).toString(),
332 };
331 });
332 next();
333 };
334}
335
336const app = express();
337
338app.use(
339 express.json({
340 verify: (req: any, _res, buf) => {
341 req.rawBody = buf?.toString() ?? "";
342 },
343 }),
344);
345
346app.use(
347 cors({
348 origin: "*",
349 exposedHeaders: ["Mcp-Session-Id"],
350 }),
351);
352
353app.use(createRequestLogger());
354
355const mcpServerUrl = new URL(`http://${CONFIG.host}:${CONFIG.port}`);
356const oauthUrls = createOAuthUrls();
357
358const oauthMetadata: OAuthMetadata = {
359 ...oauthUrls,
360 response_types_supported: ["code"],
361};
362
363const tokenVerifier = {
364 verifyAccessToken: async (token: string) => {
365 const endpoint = oauthMetadata.introspection_endpoint;
366
367 if (!endpoint) {
368 console.error("[auth] no introspection endpoint in metadata");
369 throw new Error("No token verification endpoint available in metadata");
333370 }
334371
335 function createRequestLogger() {
336 return (req: any, res: any, next: any) => {
337 const start = Date.now();
338 res.on("finish", () => {
339 const ms = Date.now() - start;
340 console.log(
341 `${req.method} ${req.originalUrl} -> ${res.statusCode} ${ms}ms`,
342 );
343 });
344 next();
345 };
372 const params = new URLSearchParams({
373 token: token,
374 client_id: CONFIG.auth.clientId,
375 });
376
377 if (CONFIG.auth.clientSecret) {
378 params.set("client_secret", CONFIG.auth.clientSecret);
346379 }
347380
348 const app = express();
349
350 app.use(
351 express.json({
352 verify: (req: any, _res, buf) => {
353 req.rawBody = buf?.toString() ?? "";
381 let response: Response;
382 try {
383 response = await fetch(endpoint, {
384 method: "POST",
385 headers: {
386 "Content-Type": "application/x-www-form-urlencoded",
354387 },
388 body: params.toString(),
389 });
390 } catch (e) {
391 console.error("[auth] introspection fetch threw", e);
392 throw e;
393 }
394
395 if (!response.ok) {
396 const txt = await response.text();
397 console.error("[auth] introspection non-OK", { status: response.status });
398
399 try {
400 const obj = JSON.parse(txt);
401 console.log(JSON.stringify(obj, null, 2));
402 } catch {
403 console.error(txt);
404 }
405 throw new Error(`Invalid or expired token: ${txt}`);
406 }
407
408 let data: any;
409 try {
410 data = await response.json();
411 } catch (e) {
412 const txt = await response.text();
413 console.error("[auth] failed to parse introspection JSON", {
414 error: String(e),
415 body: txt,
416 });
417 throw e;
418 }
419
420 if (data.active === false) {
421 throw new Error("Inactive token");
422 }
423
424 if (!data.aud) {
425 throw new Error("Resource indicator (aud) missing");
426 }
427
428 const audiences: string[] = Array.isArray(data.aud) ? data.aud : [data.aud];
429 const allowed = audiences.some((a) =>
430 checkResourceAllowed({
431 requestedResource: a,
432 configuredResource: mcpServerUrl,
355433 }),
356434 );
357
358 app.use(
359 cors({
360 origin: "*",
361 exposedHeaders: ["Mcp-Session-Id"],
362 }),
363 );
364
365 app.use(createRequestLogger());
366
367 const mcpServerUrl = new URL(`http://${CONFIG.host}:${CONFIG.port}`);
368 const oauthUrls = createOAuthUrls();
369
370 const oauthMetadata: OAuthMetadata = {
371 ...oauthUrls,
372 response_types_supported: ["code"],
435 if (!allowed) {
436 throw new Error(
437 `None of the provided audiences are allowed. Expected ${mcpServerUrl}, got: ${audiences.join(", ")}`,
438 );
439 }
440
441 return {
442 token,
443 clientId: data.client_id,
444 scopes: data.scope ? data.scope.split(" ") : [],
445 expiresAt: data.exp,
373446 };
374
375 const tokenVerifier = {
376 verifyAccessToken: async (token: string) => {
377 const endpoint = oauthMetadata.introspection_endpoint;
378
379 if (!endpoint) {
380 console.error("[auth] no introspection endpoint in metadata");
381 throw new Error("No token verification endpoint available in metadata");
447 },
448};
449app.use(
450 mcpAuthMetadataRouter({
451 oauthMetadata,
452 resourceServerUrl: mcpServerUrl,
453 scopesSupported: ["mcp:tools"],
454 resourceName: "MCP Demo Server",
455 }),
456);
457
458const authMiddleware = requireBearerAuth({
459 verifier: tokenVerifier,
460 requiredScopes: [],
461 resourceMetadataUrl: getOAuthProtectedResourceMetadataUrl(mcpServerUrl),
462});
463
464const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {};
465
466function createMcpServer() {
467 const server = new McpServer({
468 name: "example-server",
469 version: "1.0.0",
470 });
471
472 server.registerTool(
473 "add",
474 {
475 title: "Addition Tool",
476 description: "Add two numbers together",
477 inputSchema: {
478 a: z.number().describe("First number to add"),
479 b: z.number().describe("Second number to add"),
480 },
481 },
482 async ({ a, b }) => ({
483 content: [{ type: "text", text: `${a} + ${b} = ${a + b}` }],
484 }),
485 );
486
487 server.registerTool(
488 "multiply",
489 {
490 title: "Multiplication Tool",
491 description: "Multiply two numbers together",
492 inputSchema: {
493 x: z.number().describe("First number to multiply"),
494 y: z.number().describe("Second number to multiply"),
495 },
496 },
497 async ({ x, y }) => ({
498 content: [{ type: "text", text: `${x} × ${y} = ${x * y}` }],
499 }),
500 );
501
502 return server;
503}
504
505const mcpPostHandler = async (req: express.Request, res: express.Response) => {
506 const sessionId = req.headers["mcp-session-id"] as string | undefined;
507 let transport: StreamableHTTPServerTransport;
508
509 if (sessionId && transports[sessionId]) {
510 transport = transports[sessionId];
511 } else if (!sessionId && isInitializeRequest(req.body)) {
512 transport = new StreamableHTTPServerTransport({
513 sessionIdGenerator: () => randomUUID(),
514 onsessioninitialized: (sessionId) => {
515 transports[sessionId] = transport;
516 },
517 });
518
519 transport.onclose = () => {
520 if (transport.sessionId) {
521 delete transports[transport.sessionId];
522 }
523 };
524
525 const server = createMcpServer();
526 await server.connect(transport);
527 } else {
528 res.status(400).json({
529 jsonrpc: "2.0",
530 error: {
531 code: -32000,
532 message: "Bad Request: No valid session ID provided",
533 },
534 id: null,
535 });
536 return;
537 }
538
539 await transport.handleRequest(req, res, req.body);
540};
541
542const handleSessionRequest = async (
543 req: express.Request,
544 res: express.Response,
545) => {
546 const sessionId = req.headers["mcp-session-id"] as string | undefined;
547 if (!sessionId || !transports[sessionId]) {
548 res.status(400).send("Invalid or missing session ID");
549 return;
550 }
551
552 const transport = transports[sessionId];
553 await transport.handleRequest(req, res);
554};
555
556app.post("/", authMiddleware, mcpPostHandler);
557app.get("/", authMiddleware, handleSessionRequest);
558app.delete("/", authMiddleware, handleSessionRequest);
559
560app.listen(CONFIG.port, CONFIG.host, () => {
561 console.log(`🚀 MCP Server running on ${mcpServerUrl.origin}`);
562 console.log(`📡 MCP endpoint available at ${mcpServerUrl.origin}`);
563 console.log(
564 `🔐 OAuth metadata available at ${getOAuthProtectedResourceMetadataUrl(mcpServerUrl)}`,
565 );
566});
567```
568
569When you run the server, you can add it to your MCP client, such as Visual Studio Code, by providing the MCP server endpoint.
570
571For more details about implementing MCP servers in TypeScript, refer to the [TypeScript SDK documentation](https://github.com/modelcontextprotocol/typescript-sdk).
572
573**Python**
574
575You can see the complete Python project in the [sample repository](https://github.com/modelcontextprotocol/python-sdk/tree/main/examples/servers/simple-auth).
576
577To simplify our authorization interaction, in Python scenarios we rely on [FastMCP](https://gofastmcp.com/getting-started/welcome). Many of the conventions around authorization, like the endpoints and token validation logic, are consistent across languages, but some offer simpler ways of integrating them in production scenarios.
578
579Prior to writing the actual server, we need to set up our configuration in `config.py` - the contents are entirely based on your local server setup:
580
581```python theme={null}
582"""Configuration settings for the MCP auth server."""
583
584import os
585from typing import Optional
586
587
588class Config:
589 """Configuration class that loads from environment variables with sensible defaults."""
590
591 # Server settings
592 HOST: str = os.getenv("HOST", "localhost")
593 PORT: int = int(os.getenv("PORT", "3000"))
594
595 # Auth server settings
596 AUTH_HOST: str = os.getenv("AUTH_HOST", "localhost")
597 AUTH_PORT: int = int(os.getenv("AUTH_PORT", "8080"))
598 AUTH_REALM: str = os.getenv("AUTH_REALM", "master")
599
600 # OAuth client settings
601 OAUTH_CLIENT_ID: str = os.getenv("OAUTH_CLIENT_ID", "mcp-server")
602 OAUTH_CLIENT_SECRET: str = os.getenv("OAUTH_CLIENT_SECRET", "UO3rmozkFFkXr0QxPTkzZ0LMXDidIikB")
603
604 # Server settings
605 MCP_SCOPE: str = os.getenv("MCP_SCOPE", "mcp:tools")
606 OAUTH_STRICT: bool = os.getenv("OAUTH_STRICT", "false").lower() in ("true", "1", "yes")
607 TRANSPORT: str = os.getenv("TRANSPORT", "streamable-http")
608
609 @property
610 def server_url(self) -> str:
611 """Build the server URL."""
612 return f"http://{self.HOST}:{self.PORT}"
613
614 @property
615 def auth_base_url(self) -> str:
616 """Build the auth server base URL."""
617 return f"http://{self.AUTH_HOST}:{self.AUTH_PORT}/realms/{self.AUTH_REALM}/"
618
619 def validate(self) -> None:
620 """Validate configuration."""
621 if self.TRANSPORT not in ["sse", "streamable-http"]:
622 raise ValueError(f"Invalid transport: {self.TRANSPORT}. Must be 'sse' or 'streamable-http'")
623
624
625# Global configuration instance
626config = Config()
627
628```
629
630The server implementation is as follows:
631
632```python theme={null}
633import datetime
634import logging
635from typing import Any
636
637from pydantic import AnyHttpUrl
638
639from mcp.server.auth.settings import AuthSettings
640from mcp.server.fastmcp.server import FastMCP
641
642from .config import config
643from .token_verifier import IntrospectionTokenVerifier
644
645logger = logging.getLogger(__name__)
646
647
648def create_oauth_urls() -> dict[str, str]:
649 """Create OAuth URLs based on configuration (Keycloak-style)."""
650 from urllib.parse import urljoin
651
652 auth_base_url = config.auth_base_url
653
654 return {
655 "issuer": auth_base_url,
656 "introspection_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token/introspect"),
657 "authorization_endpoint": urljoin(auth_base_url, "protocol/openid-connect/auth"),
658 "token_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token"),
659 }
660
661
662def create_server() -> FastMCP:
663 """Create and configure the FastMCP server."""
664
665 config.validate()
666
667 oauth_urls = create_oauth_urls()
668
669 token_verifier = IntrospectionTokenVerifier(
670 introspection_endpoint=oauth_urls["introspection_endpoint"],
671 server_url=config.server_url,
672 client_id=config.OAUTH_CLIENT_ID,
673 client_secret=config.OAUTH_CLIENT_SECRET,
674 )
675
676 app = FastMCP(
677 name="MCP Resource Server",
678 instructions="Resource Server that validates tokens via Authorization Server introspection",
679 host=config.HOST,
680 port=config.PORT,
681 debug=True,
682 streamable_http_path="/",
683 token_verifier=token_verifier,
684 auth=AuthSettings(
685 issuer_url=AnyHttpUrl(oauth_urls["issuer"]),
686 required_scopes=[config.MCP_SCOPE],
687 resource_server_url=AnyHttpUrl(config.server_url),
688 ),
689 )
690
691 @app.tool()
692 async def add_numbers(a: float, b: float) -> dict[str, Any]:
693 """
694 Add two numbers together.
695 This tool demonstrates basic arithmetic operations with OAuth authentication.
696
697 Args:
698 a: The first number to add
699 b: The second number to add
700 """
701 result = a + b
702 return {
703 "operation": "addition",
704 "operand_a": a,
705 "operand_b": b,
706 "result": result,
707 "timestamp": datetime.datetime.now().isoformat()
382708 }
383709
384 const params = new URLSearchParams({
385 token: token,
386 client_id: CONFIG.auth.clientId,
387 });
388
389 if (CONFIG.auth.clientSecret) {
390 params.set("client_secret", CONFIG.auth.clientSecret);
710 @app.tool()
711 async def multiply_numbers(x: float, y: float) -> dict[str, Any]:
712 """
713 Multiply two numbers together.
714 This tool demonstrates basic arithmetic operations with OAuth authentication.
715
716 Args:
717 x: The first number to multiply
718 y: The second number to multiply
719 """
720 result = x * y
721 return {
722 "operation": "multiplication",
723 "operand_x": x,
724 "operand_y": y,
725 "result": result,
726 "timestamp": datetime.datetime.now().isoformat()
391727 }
392728
393 let response: Response;
394 try {
395 response = await fetch(endpoint, {
396 method: "POST",
397 headers: {
398 "Content-Type": "application/x-www-form-urlencoded",
399 },
400 body: params.toString(),
401 });
402 } catch (e) {
403 console.error("[auth] introspection fetch threw", e);
404 throw e;
729 return app
730
731
732def main() -> int:
733 """
734 Run the MCP Resource Server.
735
736 This server:
737 - Provides RFC 9728 Protected Resource Metadata
738 - Validates tokens via Authorization Server introspection
739 - Serves MCP tools requiring authentication
740
741 Configuration is loaded from config.py and environment variables.
742 """
743 logging.basicConfig(level=logging.INFO)
744
745 try:
746 config.validate()
747 oauth_urls = create_oauth_urls()
748
749 except ValueError as e:
750 logger.error("Configuration error: %s", e)
751 return 1
752
753 try:
754 mcp_server = create_server()
755
756 logger.info("Starting MCP Server on %s:%s", config.HOST, config.PORT)
757 logger.info("Authorization Server: %s", oauth_urls["issuer"])
758 logger.info("Transport: %s", config.TRANSPORT)
759
760 mcp_server.run(transport=config.TRANSPORT)
761 return 0
762
763 except Exception:
764 logger.exception("Server error")
765 return 1
766
767
768if __name__ == "__main__":
769 exit(main())
770```
771
772Lastly, the token verification logic is delegated entirely to `token_verifier.py`, ensuring that we can use the Keycloak introspection endpoint to verify the validity of any credential artifacts
773
774```python theme={null}
775"""Token verifier implementation using OAuth 2.0 Token Introspection (RFC 7662)."""
776
777import logging
778from typing import Any
779
780from mcp.server.auth.provider import AccessToken, TokenVerifier
781from mcp.shared.auth_utils import check_resource_allowed, resource_url_from_server_url
782
783logger = logging.getLogger(__name__)
784
785
786class IntrospectionTokenVerifier(TokenVerifier):
787 """Token verifier that uses OAuth 2.0 Token Introspection (RFC 7662).
788 """
789
790 def __init__(
791 self,
792 introspection_endpoint: str,
793 server_url: str,
794 client_id: str,
795 client_secret: str,
796 ):
797 self.introspection_endpoint = introspection_endpoint
798 self.server_url = server_url
799 self.client_id = client_id
800 self.client_secret = client_secret
801 self.resource_url = resource_url_from_server_url(server_url)
802
803 async def verify_token(self, token: str) -> AccessToken | None:
804 """Verify token via introspection endpoint."""
805 import httpx
806
807 if not self.introspection_endpoint.startswith(("https://", "http://localhost", "http://127.0.0.1")):
808 return None
809
810 timeout = httpx.Timeout(10.0, connect=5.0)
811 limits = httpx.Limits(max_connections=10, max_keepalive_connections=5)
812
813 async with httpx.AsyncClient(
814 timeout=timeout,
815 limits=limits,
816 verify=True,
817 ) as client:
818 try:
819 form_data = {
820 "token": token,
821 "client_id": self.client_id,
822 "client_secret": self.client_secret,
823 }
824 headers = {"Content-Type": "application/x-www-form-urlencoded"}
825
826 response = await client.post(
827 self.introspection_endpoint,
828 data=form_data,
829 headers=headers,
830 )
831
832 if response.status_code != 200:
833 return None
834
835 data = response.json()
836 if not data.get("active", False):
837 return None
838
839 if not self._validate_resource(data):
840 return None
841
842 return AccessToken(
843 token=token,
844 client_id=data.get("client_id", "unknown"),
845 scopes=data.get("scope", "").split() if data.get("scope") else [],
846 expires_at=data.get("exp"),
847 resource=data.get("aud"), # Include resource in token
848 )
849
850 except Exception as e:
851 return None
852
853 def _validate_resource(self, token_data: dict[str, Any]) -> bool:
854 """Validate token was issued for this resource server.
855
856 Rules:
857 - Reject if 'aud' missing.
858 - Accept if any audience entry matches the derived resource URL.
859 - Supports string or list forms per JWT spec.
860 """
861 if not self.server_url or not self.resource_url:
862 return False
863
864 aud: list[str] | str | None = token_data.get("aud")
865 if isinstance(aud, list):
866 return any(self._is_valid_resource(a) for a in aud)
867 if isinstance(aud, str):
868 return self._is_valid_resource(aud)
869 return False
870
871 def _is_valid_resource(self, resource: str) -> bool:
872 """Check if the given resource matches our server."""
873 return check_resource_allowed(self.resource_url, resource)
874```
875
876For more details, see the [Python SDK documentation](https://github.com/modelcontextprotocol/python-sdk).
877
878**C#**
879
880You can see the complete C# project in the [sample repository](https://github.com/localden/min-cs-mcp-auth).
881
882To set up authorization in your MCP server using the MCP C# SDK, you can lean on the standard ASP.NET Core builder pattern. Instead of using the introspection endpoint provided by Keycloak, we will use built-in ASP.NET Core capabilities for token validation.
883
884```csharp theme={null}
885using Microsoft.AspNetCore.Authentication.JwtBearer;
886using Microsoft.IdentityModel.Tokens;
887using ModelContextProtocol.AspNetCore.Authentication;
888using ProtectedMcpServer.Tools;
889using System.Security.Claims;
890
891var builder = WebApplication.CreateBuilder(args);
892
893var serverUrl = "http://localhost:3000/";
894var authorizationServerUrl = "http://localhost:8080/realms/master/";
895
896builder.Services.AddAuthentication(options =>
897{
898 options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
899 options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
900})
901.AddJwtBearer(options =>
902{
903 options.Authority = authorizationServerUrl;
904 var normalizedServerAudience = serverUrl.TrimEnd('/');
905 options.TokenValidationParameters = new TokenValidationParameters
906 {
907 ValidIssuer = authorizationServerUrl,
908 ValidAudiences = new[] { normalizedServerAudience, serverUrl },
909 AudienceValidator = (audiences, securityToken, validationParameters) =>
910 {
911 if (audiences == null) return false;
912 foreach (var aud in audiences)
913 {
914 if (string.Equals(aud.TrimEnd('/'), normalizedServerAudience, StringComparison.OrdinalIgnoreCase))
915 {
916 return true;
917 }
918 }
919 return false;
405920 }
406
407 if (!response.ok) {
408 const txt = await response.text();
409 console.error("[auth] introspection non-OK", { status: response.status });
410
411 try {
412 const obj = JSON.parse(txt);
413 console.log(JSON.stringify(obj, null, 2));
414 } catch {
415 console.error(txt);
416 }
417 throw new Error(`Invalid or expired token: ${txt}`);
418 }
419
420 let data: any;
421 try {
422 data = await response.json();
423 } catch (e) {
424 const txt = await response.text();
425 console.error("[auth] failed to parse introspection JSON", {
426 error: String(e),
427 body: txt,
428 });
429 throw e;
430 }
431
432 if (data.active === false) {
433 throw new Error("Inactive token");
434 }
435
436 if (!data.aud) {
437 throw new Error("Resource indicator (aud) missing");
438 }
439
440 const audiences: string[] = Array.isArray(data.aud) ? data.aud : [data.aud];
441 const allowed = audiences.some((a) =>
442 checkResourceAllowed({
443 requestedResource: a,
444 configuredResource: mcpServerUrl,
445 }),
446 );
447 if (!allowed) {
448 throw new Error(
449 `None of the provided audiences are allowed. Expected ${mcpServerUrl}, got: ${audiences.join(", ")}`,
450 );
451 }
452
453 return {
454 token,
455 clientId: data.client_id,
456 scopes: data.scope ? data.scope.split(" ") : [],
457 expiresAt: data.exp,
458 };
459 },
460921 };
461 app.use(
462 mcpAuthMetadataRouter({
463 oauthMetadata,
464 resourceServerUrl: mcpServerUrl,
465 scopesSupported: ["mcp:tools"],
466 resourceName: "MCP Demo Server",
467 }),
468 );
469
470 const authMiddleware = requireBearerAuth({
471 verifier: tokenVerifier,
472 requiredScopes: [],
473 resourceMetadataUrl: getOAuthProtectedResourceMetadataUrl(mcpServerUrl),
474 });
475
476 const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {};
477
478 function createMcpServer() {
479 const server = new McpServer({
480 name: "example-server",
481 version: "1.0.0",
482 });
483
484 server.registerTool(
485 "add",
922
923 options.RequireHttpsMetadata = false; // Set to true in production
924
925 options.Events = new JwtBearerEvents
926 {
927 OnTokenValidated = context =>
486928 {
487 title: "Addition Tool",
488 description: "Add two numbers together",
489 inputSchema: {
490 a: z.number().describe("First number to add"),
491 b: z.number().describe("Second number to add"),
492 },
929 var name = context.Principal?.Identity?.Name ?? "unknown";
930 var email = context.Principal?.FindFirstValue("preferred_username") ?? "unknown";
931 Console.WriteLine($"Token validated for: {name} ({email})");
932 return Task.CompletedTask;
493933 },
494 async ({ a, b }) => ({
495 content: [{ type: "text", text: `${a} + ${b} = ${a + b}` }],
496 }),
497 );
498
499 server.registerTool(
500 "multiply",
934 OnAuthenticationFailed = context =>
501935 {
502 title: "Multiplication Tool",
503 description: "Multiply two numbers together",
504 inputSchema: {
505 x: z.number().describe("First number to multiply"),
506 y: z.number().describe("Second number to multiply"),
507 },
936 Console.WriteLine($"Authentication failed: {context.Exception.Message}");
937 return Task.CompletedTask;
508938 },
509 async ({ x, y }) => ({
510 content: [{ type: "text", text: `${x} × ${y} = ${x * y}` }],
511 }),
512 );
513
514 return server;
515 }
516
517 const mcpPostHandler = async (req: express.Request, res: express.Response) => {
518 const sessionId = req.headers["mcp-session-id"] as string | undefined;
519 let transport: StreamableHTTPServerTransport;
520
521 if (sessionId && transports[sessionId]) {
522 transport = transports[sessionId];
523 } else if (!sessionId && isInitializeRequest(req.body)) {
524 transport = new StreamableHTTPServerTransport({
525 sessionIdGenerator: () => randomUUID(),
526 onsessioninitialized: (sessionId) => {
527 transports[sessionId] = transport;
528 },
529 });
530
531 transport.onclose = () => {
532 if (transport.sessionId) {
533 delete transports[transport.sessionId];
534 }
535 };
536
537 const server = createMcpServer();
538 await server.connect(transport);
539 } else {
540 res.status(400).json({
541 jsonrpc: "2.0",
542 error: {
543 code: -32000,
544 message: "Bad Request: No valid session ID provided",
545 },
546 id: null,
547 });
548 return;
549 }
550
551 await transport.handleRequest(req, res, req.body);
552939 };
553
554 const handleSessionRequest = async (
555 req: express.Request,
556 res: express.Response,
557 ) => {
558 const sessionId = req.headers["mcp-session-id"] as string | undefined;
559 if (!sessionId || !transports[sessionId]) {
560 res.status(400).send("Invalid or missing session ID");
561 return;
562 }
563
564 const transport = transports[sessionId];
565 await transport.handleRequest(req, res);
940})
941.AddMcp(options =>
942{
943 options.ResourceMetadata = new()
944 {
945 Resource = new Uri(serverUrl),
946 ResourceDocumentation = new Uri("https://docs.example.com/api/math"),
947 AuthorizationServers = { new Uri(authorizationServerUrl) },
948 ScopesSupported = ["mcp:tools"]
566949 };
567
568 app.post("/", authMiddleware, mcpPostHandler);
569 app.get("/", authMiddleware, handleSessionRequest);
570 app.delete("/", authMiddleware, handleSessionRequest);
571
572 app.listen(CONFIG.port, CONFIG.host, () => {
573 console.log(`🚀 MCP Server running on ${mcpServerUrl.origin}`);
574 console.log(`📡 MCP endpoint available at ${mcpServerUrl.origin}`);
575 console.log(
576 `🔐 OAuth metadata available at ${getOAuthProtectedResourceMetadataUrl(mcpServerUrl)}`,
577 );
578 });
579 ```
580
581 When you run the server, you can add it to your MCP client, such as Visual Studio Code, by providing the MCP server endpoint.
582
583 For more details about implementing MCP servers in TypeScript, refer to the [TypeScript SDK documentation](https://github.com/modelcontextprotocol/typescript-sdk).
584 </Tab>
585
586 <Tab title="Python">
587 You can see the complete Python project in the [sample repository](https://github.com/modelcontextprotocol/python-sdk/tree/main/examples/servers/simple-auth).
588
589 To simplify our authorization interaction, in Python scenarios we rely on [FastMCP](https://gofastmcp.com/getting-started/welcome). Many of the conventions around authorization, like the endpoints and token validation logic, are consistent across languages, but some offer simpler ways of integrating them in production scenarios.
590
591 Prior to writing the actual server, we need to set up our configuration in `config.py` - the contents are entirely based on your local server setup:
592
593 ```python theme={null}
594 """Configuration settings for the MCP auth server."""
595
596 import os
597 from typing import Optional
598
599
600 class Config:
601 """Configuration class that loads from environment variables with sensible defaults."""
602
603 # Server settings
604 HOST: str = os.getenv("HOST", "localhost")
605 PORT: int = int(os.getenv("PORT", "3000"))
606
607 # Auth server settings
608 AUTH_HOST: str = os.getenv("AUTH_HOST", "localhost")
609 AUTH_PORT: int = int(os.getenv("AUTH_PORT", "8080"))
610 AUTH_REALM: str = os.getenv("AUTH_REALM", "master")
611
612 # OAuth client settings
613 OAUTH_CLIENT_ID: str = os.getenv("OAUTH_CLIENT_ID", "mcp-server")
614 OAUTH_CLIENT_SECRET: str = os.getenv("OAUTH_CLIENT_SECRET", "UO3rmozkFFkXr0QxPTkzZ0LMXDidIikB")
615
616 # Server settings
617 MCP_SCOPE: str = os.getenv("MCP_SCOPE", "mcp:tools")
618 OAUTH_STRICT: bool = os.getenv("OAUTH_STRICT", "false").lower() in ("true", "1", "yes")
619 TRANSPORT: str = os.getenv("TRANSPORT", "streamable-http")
620
621 @property
622 def server_url(self) -> str:
623 """Build the server URL."""
624 return f"http://{self.HOST}:{self.PORT}"
625
626 @property
627 def auth_base_url(self) -> str:
628 """Build the auth server base URL."""
629 return f"http://{self.AUTH_HOST}:{self.AUTH_PORT}/realms/{self.AUTH_REALM}/"
630
631 def validate(self) -> None:
632 """Validate configuration."""
633 if self.TRANSPORT not in ["sse", "streamable-http"]:
634 raise ValueError(f"Invalid transport: {self.TRANSPORT}. Must be 'sse' or 'streamable-http'")
635
636
637 # Global configuration instance
638 config = Config()
639
640 ```
641
642 The server implementation is as follows:
643
644 ```python theme={null}
645 import datetime
646 import logging
647 from typing import Any
648
649 from pydantic import AnyHttpUrl
650
651 from mcp.server.auth.settings import AuthSettings
652 from mcp.server.fastmcp.server import FastMCP
653
654 from .config import config
655 from .token_verifier import IntrospectionTokenVerifier
656
657 logger = logging.getLogger(__name__)
658
659
660 def create_oauth_urls() -> dict[str, str]:
661 """Create OAuth URLs based on configuration (Keycloak-style)."""
662 from urllib.parse import urljoin
663
664 auth_base_url = config.auth_base_url
665
666 return {
667 "issuer": auth_base_url,
668 "introspection_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token/introspect"),
669 "authorization_endpoint": urljoin(auth_base_url, "protocol/openid-connect/auth"),
670 "token_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token"),
671 }
672
673
674 def create_server() -> FastMCP:
675 """Create and configure the FastMCP server."""
676
677 config.validate()
678
679 oauth_urls = create_oauth_urls()
680
681 token_verifier = IntrospectionTokenVerifier(
682 introspection_endpoint=oauth_urls["introspection_endpoint"],
683 server_url=config.server_url,
684 client_id=config.OAUTH_CLIENT_ID,
685 client_secret=config.OAUTH_CLIENT_SECRET,
686 )
687
688 app = FastMCP(
689 name="MCP Resource Server",
690 instructions="Resource Server that validates tokens via Authorization Server introspection",
691 host=config.HOST,
692 port=config.PORT,
693 debug=True,
694 streamable_http_path="/",
695 token_verifier=token_verifier,
696 auth=AuthSettings(
697 issuer_url=AnyHttpUrl(oauth_urls["issuer"]),
698 required_scopes=[config.MCP_SCOPE],
699 resource_server_url=AnyHttpUrl(config.server_url),
700 ),
701 )
702
703 @app.tool()
704 async def add_numbers(a: float, b: float) -> dict[str, Any]:
705 """
706 Add two numbers together.
707 This tool demonstrates basic arithmetic operations with OAuth authentication.
708
709 Args:
710 a: The first number to add
711 b: The second number to add
712 """
713 result = a + b
714 return {
715 "operation": "addition",
716 "operand_a": a,
717 "operand_b": b,
718 "result": result,
719 "timestamp": datetime.datetime.now().isoformat()
720 }
721
722 @app.tool()
723 async def multiply_numbers(x: float, y: float) -> dict[str, Any]:
724 """
725 Multiply two numbers together.
726 This tool demonstrates basic arithmetic operations with OAuth authentication.
727
728 Args:
729 x: The first number to multiply
730 y: The second number to multiply
731 """
732 result = x * y
733 return {
734 "operation": "multiplication",
735 "operand_x": x,
736 "operand_y": y,
737 "result": result,
738 "timestamp": datetime.datetime.now().isoformat()
739 }
740
741 return app
742
743
744 def main() -> int:
745 """
746 Run the MCP Resource Server.
747
748 This server:
749 - Provides RFC 9728 Protected Resource Metadata
750 - Validates tokens via Authorization Server introspection
751 - Serves MCP tools requiring authentication
752
753 Configuration is loaded from config.py and environment variables.
754 """
755 logging.basicConfig(level=logging.INFO)
756
757 try:
758 config.validate()
759 oauth_urls = create_oauth_urls()
760
761 except ValueError as e:
762 logger.error("Configuration error: %s", e)
763 return 1
764
765 try:
766 mcp_server = create_server()
767
768 logger.info("Starting MCP Server on %s:%s", config.HOST, config.PORT)
769 logger.info("Authorization Server: %s", oauth_urls["issuer"])
770 logger.info("Transport: %s", config.TRANSPORT)
771
772 mcp_server.run(transport=config.TRANSPORT)
773 return 0
774
775 except Exception:
776 logger.exception("Server error")
777 return 1
778
779
780 if __name__ == "__main__":
781 exit(main())
782 ```
783
784 Lastly, the token verification logic is delegated entirely to `token_verifier.py`, ensuring that we can use the Keycloak introspection endpoint to verify the validity of any credential artifacts
785
786 ```python theme={null}
787 """Token verifier implementation using OAuth 2.0 Token Introspection (RFC 7662)."""
788
789 import logging
790 from typing import Any
791
792 from mcp.server.auth.provider import AccessToken, TokenVerifier
793 from mcp.shared.auth_utils import check_resource_allowed, resource_url_from_server_url
794
795 logger = logging.getLogger(__name__)
796
797
798 class IntrospectionTokenVerifier(TokenVerifier):
799 """Token verifier that uses OAuth 2.0 Token Introspection (RFC 7662).
800 """
801
802 def __init__(
803 self,
804 introspection_endpoint: str,
805 server_url: str,
806 client_id: str,
807 client_secret: str,
808 ):
809 self.introspection_endpoint = introspection_endpoint
810 self.server_url = server_url
811 self.client_id = client_id
812 self.client_secret = client_secret
813 self.resource_url = resource_url_from_server_url(server_url)
814
815 async def verify_token(self, token: str) -> AccessToken | None:
816 """Verify token via introspection endpoint."""
817 import httpx
818
819 if not self.introspection_endpoint.startswith(("https://", "http://localhost", "http://127.0.0.1")):
820 return None
821
822 timeout = httpx.Timeout(10.0, connect=5.0)
823 limits = httpx.Limits(max_connections=10, max_keepalive_connections=5)
824
825 async with httpx.AsyncClient(
826 timeout=timeout,
827 limits=limits,
828 verify=True,
829 ) as client:
830 try:
831 form_data = {
832 "token": token,
833 "client_id": self.client_id,
834 "client_secret": self.client_secret,
835 }
836 headers = {"Content-Type": "application/x-www-form-urlencoded"}
837
838 response = await client.post(
839 self.introspection_endpoint,
840 data=form_data,
841 headers=headers,
842 )
843
844 if response.status_code != 200:
845 return None
846
847 data = response.json()
848 if not data.get("active", False):
849 return None
850
851 if not self._validate_resource(data):
852 return None
853
854 return AccessToken(
855 token=token,
856 client_id=data.get("client_id", "unknown"),
857 scopes=data.get("scope", "").split() if data.get("scope") else [],
858 expires_at=data.get("exp"),
859 resource=data.get("aud"), # Include resource in token
860 )
861
862 except Exception as e:
863 return None
864
865 def _validate_resource(self, token_data: dict[str, Any]) -> bool:
866 """Validate token was issued for this resource server.
867
868 Rules:
869 - Reject if 'aud' missing.
870 - Accept if any audience entry matches the derived resource URL.
871 - Supports string or list forms per JWT spec.
872 """
873 if not self.server_url or not self.resource_url:
874 return False
875
876 aud: list[str] | str | None = token_data.get("aud")
877 if isinstance(aud, list):
878 return any(self._is_valid_resource(a) for a in aud)
879 if isinstance(aud, str):
880 return self._is_valid_resource(aud)
881 return False
882
883 def _is_valid_resource(self, resource: str) -> bool:
884 """Check if the given resource matches our server."""
885 return check_resource_allowed(self.resource_url, resource)
886 ```
887
888 For more details, see the [Python SDK documentation](https://github.com/modelcontextprotocol/python-sdk).
889 </Tab>
890
891 <Tab title="C#">
892 You can see the complete C# project in the [sample repository](https://github.com/localden/min-cs-mcp-auth).
893
894 To set up authorization in your MCP server using the MCP C# SDK, you can lean on the standard ASP.NET Core builder pattern. Instead of using the introspection endpoint provided by Keycloak, we will use built-in ASP.NET Core capabilities for token validation.
895
896 ```csharp theme={null}
897 using Microsoft.AspNetCore.Authentication.JwtBearer;
898 using Microsoft.IdentityModel.Tokens;
899 using ModelContextProtocol.AspNetCore.Authentication;
900 using ProtectedMcpServer.Tools;
901 using System.Security.Claims;
902
903 var builder = WebApplication.CreateBuilder(args);
904
905 var serverUrl = "http://localhost:3000/";
906 var authorizationServerUrl = "http://localhost:8080/realms/master/";
907
908 builder.Services.AddAuthentication(options =>
909 {
910 options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
911 options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
912 })
913 .AddJwtBearer(options =>
914 {
915 options.Authority = authorizationServerUrl;
916 var normalizedServerAudience = serverUrl.TrimEnd('/');
917 options.TokenValidationParameters = new TokenValidationParameters
918 {
919 ValidIssuer = authorizationServerUrl,
920 ValidAudiences = new[] { normalizedServerAudience, serverUrl },
921 AudienceValidator = (audiences, securityToken, validationParameters) =>
922 {
923 if (audiences == null) return false;
924 foreach (var aud in audiences)
925 {
926 if (string.Equals(aud.TrimEnd('/'), normalizedServerAudience, StringComparison.OrdinalIgnoreCase))
927 {
928 return true;
929 }
930 }
931 return false;
932 }
933 };
934
935 options.RequireHttpsMetadata = false; // Set to true in production
936
937 options.Events = new JwtBearerEvents
938 {
939 OnTokenValidated = context =>
940 {
941 var name = context.Principal?.Identity?.Name ?? "unknown";
942 var email = context.Principal?.FindFirstValue("preferred_username") ?? "unknown";
943 Console.WriteLine($"Token validated for: {name} ({email})");
944 return Task.CompletedTask;
945 },
946 OnAuthenticationFailed = context =>
947 {
948 Console.WriteLine($"Authentication failed: {context.Exception.Message}");
949 return Task.CompletedTask;
950 },
951 };
952 })
953 .AddMcp(options =>
954 {
955 options.ResourceMetadata = new()
956 {
957 Resource = new Uri(serverUrl),
958 ResourceDocumentation = new Uri("https://docs.example.com/api/math"),
959 AuthorizationServers = { new Uri(authorizationServerUrl) },
960 ScopesSupported = ["mcp:tools"]
961 };
962 });
963
964 builder.Services.AddAuthorization();
965
966 builder.Services.AddHttpContextAccessor();
967 builder.Services.AddMcpServer()
968 .WithTools<MathTools>()
969 .WithHttpTransport();
970
971 var app = builder.Build();
972
973 app.UseAuthentication();
974 app.UseAuthorization();
975
976 app.MapMcp().RequireAuthorization();
977
978 Console.WriteLine($"Starting MCP server with authorization at {serverUrl}");
979 Console.WriteLine($"Using Keycloak server at {authorizationServerUrl}");
980 Console.WriteLine($"Protected Resource Metadata URL: {serverUrl}.well-known/oauth-protected-resource");
981 Console.WriteLine("Exposed Math tools: Add, Multiply");
982 Console.WriteLine("Press Ctrl+C to stop the server");
983
984 app.Run(serverUrl);
985 ```
986
987 For more details, see the [C# SDK documentation](https://github.com/modelcontextprotocol/csharp-sdk).
988 </Tab>
989</Tabs>
950});
951
952builder.Services.AddAuthorization();
953
954builder.Services.AddHttpContextAccessor();
955builder.Services.AddMcpServer()
956 .WithTools<MathTools>()
957 .WithHttpTransport();
958
959var app = builder.Build();
960
961app.UseAuthentication();
962app.UseAuthorization();
963
964app.MapMcp().RequireAuthorization();
965
966Console.WriteLine($"Starting MCP server with authorization at {serverUrl}");
967Console.WriteLine($"Using Keycloak server at {authorizationServerUrl}");
968Console.WriteLine($"Protected Resource Metadata URL: {serverUrl}.well-known/oauth-protected-resource");
969Console.WriteLine("Exposed Math tools: Add, Multiply");
970Console.WriteLine("Press Ctrl+C to stop the server");
971
972app.Run(serverUrl);
973```
974
975For more details, see the [C# SDK documentation](https://github.com/modelcontextprotocol/csharp-sdk).
990976
991977## Testing the MCP Server
992978
from line 989
1003989
1004990On connection, you will be taken to the browser, where you will be prompted to consent to Visual Studio Code having access to the `mcp:tools` scope.
1005991
1006<Frame>
1007 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-vscode.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=d5183fb7c257993aed1b2246f0bbbb27" alt="Keycloak consent form for VS Code." width="1915" height="1536" data-path="images/tutorial-authorization/keycloak-vscode.png" />
1008</Frame>
992
1009993
1010994After consenting, you will see the tools listed right above the server entry in `mcp.json`.
1011995
1012<Frame>
1013 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/tools-vs-code.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=f7c34d1bf115fe6934e01b4a5a91168b" alt="Tools listed in VS Code." width="496" height="160" data-path="images/tutorial-authorization/tools-vs-code.png" />
1014</Frame>
996
1015997
1016998You will be able to invoke individual tools with the help of the `#` sign in the chat view.
1017999
1018<Frame>
1019 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/tools-vs-code-invoke.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=76cbef68e48821a3c5467bd20c7e89fe" alt="Invoking MCP tools in VS Code." width="1276" height="396" data-path="images/tutorial-authorization/tools-vs-code-invoke.png" />
1020</Frame>
1000
10211001
10221002## Common Pitfalls and How to Avoid Them
10231003
10241004
docs/2025-06-18/tutorials/security/security_best_practices Changed · +4 / -4 lines
from line 423
423423* Link-local: `169.254.0.0/16` (including cloud metadata endpoints)
424424* Private IPv6 ranges: `fc00::/7`, `fe80::/10`
425425
426<Note>
427 Avoid implementing IP validation manually. Attackers exploit encoding tricks
428 (octal, hex, IPv4-mapped IPv6) that custom parsers often miss.
429</Note>
426> [!NOTE]
427>
428> Avoid implementing IP validation manually. Attackers exploit encoding tricks
429> (octal, hex, IPv4-mapped IPv6) that custom parsers often miss.
430430
431431**Validate Redirect Targets**
432432
docs/2025-11-25/develop/build-client Changed · +2444 / -2460 lines
## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Basic Client Structure ### Server Connection Management ### Query Processing Logic ### Interactive Chat Interface ### Main Entry Point ## Key Components Explained ### 1. Client Initialization ### 2. Server Connection ### 3. Query Processing ### 4. Interactive Interface ### 5. Resource Management ## Common Customization Points ## Running the Client ## How It Works ## Best practices ## Troubleshooting ### Server Path Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Basic Client Structure ### Server Connection Management ### Query Processing Logic ### Interactive Chat Interface ### Main Entry Point ## Running the Client ## How It Works ## Best practices ## Troubleshooting ### Server Path Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting Up Your Environment ## How it Works ### MCP Client Configuration ### Chat Implementation ### Build and run ### Advanced Configuration ## System Requirements ## Setting up your environment ## Setting up your API key ## Creating the Client ### Basic Client Structure ### Server connection management ### Query processing logic ### Interactive chat ### Main entry point ## Running the client ## How it works ## Best practices ## Troubleshooting ### Server Path Issues ### Build Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting up your environment ## Setting up your API key ## Creating the Client ### Basic Client Structure ### Query processing logic ## Key Components Explained ### 1. Client Initialization ### 2. Server Connection ### 3. Query Processing ## Running the Client ## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Basic Client Structure ### Server Connection Management ### Query Processing Logic ### Interactive Chat Interface ### Main Entry Point ## Key Components Explained ### 1. Client Initialization ### 2. Server Connection ### 3. Query Processing ### 4. Interactive Interface ### 5. Resource Management ## Running the Client ## How It Works ## Best practices ## Troubleshooting ### Server Path Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Imports and Client Structure ### Client Initialization ### Server Connection Management ### Converting MCP Tools ### Sending Model Requests ### Query Processing Logic ### Interactive Chat Interface ### Cleanup ### Main Entry Point ### Verify the Complete File ## Running the Client ## How It Works ## Best Practices ## Troubleshooting ### Server Command Issues ### Environment File Issues ### Tool and Response Errors
The two sides of this change are more than 400 edits apart, too far apart to line up, so this is the differ's own diff of it and the words inside a line are not marked.
from line 6
66
77Before you begin, it helps to have gone through our [Build an MCP Server](/docs/2025-11-25/develop/build-server) tutorial so you can understand how clients and servers communicate.
88
9<Tabs>
10 <Tab title="Python">
11 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-python)
12
13 ## System Requirements
14
15 Before starting, ensure your system meets these requirements:
16
17 * Mac or Windows computer
18 * Latest Python version installed
19 * Latest version of `uv` installed
20
21 ## Setting Up Your Environment
22
23 First, create a new Python project with `uv`:
24
25 <CodeGroup>
26 ```bash macOS/Linux theme={null}
27 # Create project directory
28 uv init mcp-client
29 cd mcp-client
30
31 # Create virtual environment
32 uv venv
33
34 # Activate virtual environment
35 source .venv/bin/activate
36
37 # Install required packages
38 uv add mcp anthropic python-dotenv
39
40 # Remove boilerplate files
41 rm main.py
42
43 # Create our main file
44 touch client.py
45 ```
46
47 ```powershell Windows theme={null}
48 # Create project directory
49 uv init mcp-client
50 cd mcp-client
51
52 # Create virtual environment
53 uv venv
54
55 # Activate virtual environment
56 .venv\Scripts\activate
57
58 # Install required packages
59 uv add mcp anthropic python-dotenv
60
61 # Remove boilerplate files
62 del main.py
63
64 # Create our main file
65 new-item client.py
66 ```
67 </CodeGroup>
68
69 ## Setting Up Your API Key
70
71 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
72
73 Create a `.env` file to store it:
74
75 ```bash theme={null}
76 echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
77 ```
78
79 Add `.env` to your `.gitignore`:
80
81 ```bash theme={null}
82 echo ".env" >> .gitignore
83 ```
84
85 <Warning>
86 Make sure you keep your `ANTHROPIC_API_KEY` secure!
87 </Warning>
88
89 ## Creating the Client
90
91 ### Basic Client Structure
92
93 First, let's set up our imports and create the basic client class:
94
95 ```python theme={null}
96 import asyncio
97 from typing import Optional
98 from contextlib import AsyncExitStack
99
100 from mcp import ClientSession, StdioServerParameters
101 from mcp.client.stdio import stdio_client
102
103 from anthropic import Anthropic
104 from dotenv import load_dotenv
105
106 load_dotenv() # load environment variables from .env
107
108 class MCPClient:
109 def __init__(self):
110 # Initialize session and client objects
111 self.session: Optional[ClientSession] = None
112 self.exit_stack = AsyncExitStack()
113 self.anthropic = Anthropic()
114 # methods will go here
115 ```
116
117 ### Server Connection Management
118
119 Next, we'll implement the method to connect to an MCP server:
120
121 ```python theme={null}
122 async def connect_to_server(self, server_script_path: str):
123 """Connect to an MCP server
124
125 Args:
126 server_script_path: Path to the server script (.py or .js)
127 """
128 is_python = server_script_path.endswith('.py')
129 is_js = server_script_path.endswith('.js')
130 if not (is_python or is_js):
131 raise ValueError("Server script must be a .py or .js file")
132
133 command = "python" if is_python else "node"
134 server_params = StdioServerParameters(
135 command=command,
136 args=[server_script_path],
137 env=None
138 )
139
140 stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
141 self.stdio, self.write = stdio_transport
142 self.session = await self.exit_stack.enter_async_context(ClientSession(self.stdio, self.write))
143
144 await self.session.initialize()
145
146 # List available tools
147 response = await self.session.list_tools()
148 tools = response.tools
149 print("\nConnected to server with tools:", [tool.name for tool in tools])
150 ```
151
152 ### Query Processing Logic
153
154 Now let's add the core functionality for processing queries and handling tool calls:
155
156 ```python theme={null}
157 async def process_query(self, query: str) -> str:
158 """Process a query using Claude and available tools"""
159 messages = [
160 {
9**Python**
10
11[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-python)
12
13## System Requirements
14
15Before starting, ensure your system meets these requirements:
16
17* Mac or Windows computer
18* Latest Python version installed
19* Latest version of `uv` installed
20
21## Setting Up Your Environment
22
23First, create a new Python project with `uv`:
24
25```bash macOS/Linux theme={null}
26# Create project directory
27uv init mcp-client
28cd mcp-client
29
30# Create virtual environment
31uv venv
32
33# Activate virtual environment
34source .venv/bin/activate
35
36# Install required packages
37uv add mcp anthropic python-dotenv
38
39# Remove boilerplate files
40rm main.py
41
42# Create our main file
43touch client.py
44```
45
46```powershell Windows theme={null}
47# Create project directory
48uv init mcp-client
49cd mcp-client
50
51# Create virtual environment
52uv venv
53
54# Activate virtual environment
55.venv\Scripts\activate
56
57# Install required packages
58uv add mcp anthropic python-dotenv
59
60# Remove boilerplate files
61del main.py
62
63# Create our main file
64new-item client.py
65```
66
67## Setting Up Your API Key
68
69You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
70
71Create a `.env` file to store it:
72
73```bash theme={null}
74echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
75```
76
77Add `.env` to your `.gitignore`:
78
79```bash theme={null}
80echo ".env" >> .gitignore
81```
82
83> [!WARNING]
84>
85> Make sure you keep your `ANTHROPIC_API_KEY` secure!
86
87## Creating the Client
88
89### Basic Client Structure
90
91First, let's set up our imports and create the basic client class:
92
93```python theme={null}
94import asyncio
95from typing import Optional
96from contextlib import AsyncExitStack
97
98from mcp import ClientSession, StdioServerParameters
99from mcp.client.stdio import stdio_client
100
101from anthropic import Anthropic
102from dotenv import load_dotenv
103
104load_dotenv() # load environment variables from .env
105
106class MCPClient:
107 def __init__(self):
108 # Initialize session and client objects
109 self.session: Optional[ClientSession] = None
110 self.exit_stack = AsyncExitStack()
111 self.anthropic = Anthropic()
112 # methods will go here
113```
114
115### Server Connection Management
116
117Next, we'll implement the method to connect to an MCP server:
118
119```python theme={null}
120async def connect_to_server(self, server_script_path: str):
121 """Connect to an MCP server
122
123 Args:
124 server_script_path: Path to the server script (.py or .js)
125 """
126 is_python = server_script_path.endswith('.py')
127 is_js = server_script_path.endswith('.js')
128 if not (is_python or is_js):
129 raise ValueError("Server script must be a .py or .js file")
130
131 command = "python" if is_python else "node"
132 server_params = StdioServerParameters(
133 command=command,
134 args=[server_script_path],
135 env=None
136 )
137
138 stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
139 self.stdio, self.write = stdio_transport
140 self.session = await self.exit_stack.enter_async_context(ClientSession(self.stdio, self.write))
141
142 await self.session.initialize()
143
144 # List available tools
145 response = await self.session.list_tools()
146 tools = response.tools
147 print("\nConnected to server with tools:", [tool.name for tool in tools])
148```
149
150### Query Processing Logic
151
152Now let's add the core functionality for processing queries and handling tool calls:
153
154```python theme={null}
155async def process_query(self, query: str) -> str:
156 """Process a query using Claude and available tools"""
157 messages = [
158 {
159 "role": "user",
160 "content": query
161 }
162 ]
163
164 response = await self.session.list_tools()
165 available_tools = [{
166 "name": tool.name,
167 "description": tool.description,
168 "input_schema": tool.inputSchema
169 } for tool in response.tools]
170
171 # Initial Claude API call
172 response = self.anthropic.messages.create(
173 model="claude-sonnet-4-20250514",
174 max_tokens=1000,
175 messages=messages,
176 tools=available_tools
177 )
178
179 # Process response and handle tool calls
180 final_text = []
181
182 assistant_message_content = []
183 for content in response.content:
184 if content.type == 'text':
185 final_text.append(content.text)
186 assistant_message_content.append(content)
187 elif content.type == 'tool_use':
188 tool_name = content.name
189 tool_args = content.input
190
191 # Execute tool call
192 result = await self.session.call_tool(tool_name, tool_args)
193 final_text.append(f"[Calling tool {tool_name} with args {tool_args}]")
194
195 assistant_message_content.append(content)
196 messages.append({
197 "role": "assistant",
198 "content": assistant_message_content
199 })
200 messages.append({
161201 "role": "user",
162 "content": query
163 }
164 ]
165
166 response = await self.session.list_tools()
167 available_tools = [{
168 "name": tool.name,
169 "description": tool.description,
170 "input_schema": tool.inputSchema
171 } for tool in response.tools]
172
173 # Initial Claude API call
174 response = self.anthropic.messages.create(
175 model="claude-sonnet-4-20250514",
176 max_tokens=1000,
177 messages=messages,
178 tools=available_tools
179 )
180
181 # Process response and handle tool calls
182 final_text = []
183
184 assistant_message_content = []
185 for content in response.content:
186 if content.type == 'text':
187 final_text.append(content.text)
188 assistant_message_content.append(content)
189 elif content.type == 'tool_use':
190 tool_name = content.name
191 tool_args = content.input
192
193 # Execute tool call
194 result = await self.session.call_tool(tool_name, tool_args)
195 final_text.append(f"[Calling tool {tool_name} with args {tool_args}]")
196
197 assistant_message_content.append(content)
198 messages.append({
199 "role": "assistant",
200 "content": assistant_message_content
201 })
202 messages.append({
203 "role": "user",
204 "content": [
205 {
206 "type": "tool_result",
207 "tool_use_id": content.id,
208 "content": result.content
209 }
210 ]
211 })
212
213 # Get next response from Claude
214 response = self.anthropic.messages.create(
215 model="claude-sonnet-4-20250514",
216 max_tokens=1000,
217 messages=messages,
218 tools=available_tools
219 )
220
221 final_text.append(response.content[0].text)
222
223 return "\n".join(final_text)
224 ```
225
226 ### Interactive Chat Interface
227
228 Now we'll add the chat loop and cleanup functionality:
229
230 ```python theme={null}
231 async def chat_loop(self):
232 """Run an interactive chat loop"""
233 print("\nMCP Client Started!")
234 print("Type your queries or 'quit' to exit.")
235
236 while True:
237 try:
238 query = input("\nQuery: ").strip()
239
240 if query.lower() == 'quit':
241 break
242
243 response = await self.process_query(query)
244 print("\n" + response)
245
246 except Exception as e:
247 print(f"\nError: {str(e)}")
248
249 async def cleanup(self):
250 """Clean up resources"""
251 await self.exit_stack.aclose()
252 ```
253
254 ### Main Entry Point
255
256 Finally, we'll add the main execution logic:
257
258 ```python theme={null}
259 async def main():
260 if len(sys.argv) < 2:
261 print("Usage: python client.py <path_to_server_script>")
262 sys.exit(1)
263
264 client = MCPClient()
202 "content": [
203 {
204 "type": "tool_result",
205 "tool_use_id": content.id,
206 "content": result.content
207 }
208 ]
209 })
210
211 # Get next response from Claude
212 response = self.anthropic.messages.create(
213 model="claude-sonnet-4-20250514",
214 max_tokens=1000,
215 messages=messages,
216 tools=available_tools
217 )
218
219 final_text.append(response.content[0].text)
220
221 return "\n".join(final_text)
222```
223
224### Interactive Chat Interface
225
226Now we'll add the chat loop and cleanup functionality:
227
228```python theme={null}
229async def chat_loop(self):
230 """Run an interactive chat loop"""
231 print("\nMCP Client Started!")
232 print("Type your queries or 'quit' to exit.")
233
234 while True:
265235 try:
266 await client.connect_to_server(sys.argv[1])
267 await client.chat_loop()
268 finally:
269 await client.cleanup()
270
271 if __name__ == "__main__":
272 import sys
273 asyncio.run(main())
274 ```
275
276 You can find the complete `client.py` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-python/client.py).
277
278 ## Key Components Explained
279
280 ### 1. Client Initialization
281
282 * The `MCPClient` class initializes with session management and API clients
283 * Uses `AsyncExitStack` for proper resource management
284 * Configures the Anthropic client for Claude interactions
285
286 ### 2. Server Connection
287
288 * Supports both Python and Node.js servers
289 * Validates server script type
290 * Sets up proper communication channels
291 * Initializes the session and lists available tools
292
293 ### 3. Query Processing
294
295 * Maintains conversation context
296 * Handles Claude's responses and tool calls
297 * Manages the message flow between Claude and tools
298 * Combines results into a coherent response
299
300 ### 4. Interactive Interface
301
302 * Provides a simple command-line interface
303 * Handles user input and displays responses
304 * Includes basic error handling
305 * Allows graceful exit
306
307 ### 5. Resource Management
308
309 * Proper cleanup of resources
310 * Error handling for connection issues
311 * Graceful shutdown procedures
312
313 ## Common Customization Points
314
315 1. **Tool Handling**
316 * Modify `process_query()` to handle specific tool types
317 * Add custom error handling for tool calls
318 * Implement tool-specific response formatting
319
320 2. **Response Processing**
321 * Customize how tool results are formatted
322 * Add response filtering or transformation
323 * Implement custom logging
324
325 3. **User Interface**
326 * Add a GUI or web interface
327 * Implement rich console output
328 * Add command history or auto-completion
329
330 ## Running the Client
331
332 To run your client with any MCP server:
333
334 ```bash theme={null}
335 uv run client.py path/to/server.py # python server
336 uv run client.py path/to/build/index.js # node server
337 ```
338
339 <Note>
340 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python), your command might look something like this: `python client.py .../quickstart-resources/weather-server-python/weather.py`
341 </Note>
342
343 The client will:
344
345 1. Connect to the specified server
346 2. List available tools
347 3. Start an interactive chat session where you can:
348 * Enter queries
349 * See tool executions
350 * Get responses from Claude
351
352 Here's an example of what it should look like if connected to the weather server from the server quickstart:
353
354 <Frame>
355 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/client-claude-cli-python.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=686d6e0ae7c54f807827db111eaed7d4" width="1932" height="1739" data-path="images/client-claude-cli-python.png" />
356 </Frame>
357
358 ## How It Works
359
360 When you submit a query:
361
362 1. The client gets the list of available tools from the server
363 2. Your query is sent to Claude along with tool descriptions
364 3. Claude decides which tools (if any) to use
365 4. The client executes any requested tool calls through the server
366 5. Results are sent back to Claude
367 6. Claude provides a natural language response
368 7. The response is displayed to you
369
370 ## Best practices
371
372 1. **Error Handling**
373 * Always wrap tool calls in try-catch blocks
374 * Provide meaningful error messages
375 * Gracefully handle connection issues
376
377 2. **Resource Management**
378 * Use `AsyncExitStack` for proper cleanup
379 * Close connections when done
380 * Handle server disconnections
381
382 3. **Security**
383 * Store API keys securely in `.env`
384 * Validate server responses
385 * Be cautious with tool permissions
386
387 4. **Tool Names**
388 * Tool names can be validated according to the format specified [here](/specification/2025-11-25/server/tools#tool-names)
389 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
390
391 ## Troubleshooting
392
393 ### Server Path Issues
394
395 * Double-check the path to your server script is correct
396 * Use the absolute path if the relative path isn't working
397 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
398 * Verify the server file has the correct extension (.py for Python or .js for Node.js)
399
400 Example of correct path usage:
401
402 ```bash theme={null}
403 # Relative path
404 uv run client.py ./server/weather.py
405
406 # Absolute path
407 uv run client.py /Users/username/projects/mcp-server/weather.py
408
409 # Windows path (either format works)
410 uv run client.py C:/projects/mcp-server/weather.py
411 uv run client.py C:\\projects\\mcp-server\\weather.py
412 ```
413
414 ### Response Timing
415
416 * The first response might take up to 30 seconds to return
417 * This is normal and happens while:
418 * The server initializes
419 * Claude processes the query
420 * Tools are being executed
421 * Subsequent responses are typically faster
422 * Don't interrupt the process during this initial waiting period
423
424 ### Common Error Messages
425
426 If you see:
427
428 * `FileNotFoundError`: Check your server path
429 * `Connection refused`: Ensure the server is running and the path is correct
430 * `Tool execution failed`: Verify the tool's required environment variables are set
431 * `Timeout error`: Consider increasing the timeout in your client configuration
432 </Tab>
433
434 <Tab title="TypeScript">
435 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-typescript)
436
437 ## System Requirements
438
439 Before starting, ensure your system meets these requirements:
440
441 * Mac or Windows computer
442 * Node.js 17 or higher installed
443 * Latest version of `npm` installed
444 * Anthropic API key (Claude)
445
446 ## Setting Up Your Environment
447
448 First, let's create and set up our project:
449
450 <CodeGroup>
451 ```bash macOS/Linux theme={null}
452 # Create project directory
453 mkdir mcp-client-typescript
454 cd mcp-client-typescript
455
456 # Initialize npm project
457 npm init -y
458
459 # Install dependencies
460 npm install @anthropic-ai/sdk @modelcontextprotocol/sdk dotenv
461
462 # Install dev dependencies
463 npm install -D @types/node typescript
464
465 # Create source file
466 touch index.ts
467 ```
468
469 ```powershell Windows theme={null}
470 # Create project directory
471 md mcp-client-typescript
472 cd mcp-client-typescript
473
474 # Initialize npm project
475 npm init -y
476
477 # Install dependencies
478 npm install @anthropic-ai/sdk @modelcontextprotocol/sdk dotenv
479
480 # Install dev dependencies
481 npm install -D @types/node typescript
482
483 # Create source file
484 new-item index.ts
485 ```
486 </CodeGroup>
487
488 Update your `package.json` to set `type: "module"` and a build script:
489
490 ```json package.json theme={null}
236 query = input("\nQuery: ").strip()
237
238 if query.lower() == 'quit':
239 break
240
241 response = await self.process_query(query)
242 print("\n" + response)
243
244 except Exception as e:
245 print(f"\nError: {str(e)}")
246
247async def cleanup(self):
248 """Clean up resources"""
249 await self.exit_stack.aclose()
250```
251
252### Main Entry Point
253
254Finally, we'll add the main execution logic:
255
256```python theme={null}
257async def main():
258 if len(sys.argv) < 2:
259 print("Usage: python client.py <path_to_server_script>")
260 sys.exit(1)
261
262 client = MCPClient()
263 try:
264 await client.connect_to_server(sys.argv[1])
265 await client.chat_loop()
266 finally:
267 await client.cleanup()
268
269if __name__ == "__main__":
270 import sys
271 asyncio.run(main())
272```
273
274You can find the complete `client.py` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-python/client.py).
275
276## Key Components Explained
277
278### 1. Client Initialization
279
280* The `MCPClient` class initializes with session management and API clients
281* Uses `AsyncExitStack` for proper resource management
282* Configures the Anthropic client for Claude interactions
283
284### 2. Server Connection
285
286* Supports both Python and Node.js servers
287* Validates server script type
288* Sets up proper communication channels
289* Initializes the session and lists available tools
290
291### 3. Query Processing
292
293* Maintains conversation context
294* Handles Claude's responses and tool calls
295* Manages the message flow between Claude and tools
296* Combines results into a coherent response
297
298### 4. Interactive Interface
299
300* Provides a simple command-line interface
301* Handles user input and displays responses
302* Includes basic error handling
303* Allows graceful exit
304
305### 5. Resource Management
306
307* Proper cleanup of resources
308* Error handling for connection issues
309* Graceful shutdown procedures
310
311## Common Customization Points
312
3131. **Tool Handling**
314 * Modify `process_query()` to handle specific tool types
315 * Add custom error handling for tool calls
316 * Implement tool-specific response formatting
317
3182. **Response Processing**
319 * Customize how tool results are formatted
320 * Add response filtering or transformation
321 * Implement custom logging
322
3233. **User Interface**
324 * Add a GUI or web interface
325 * Implement rich console output
326 * Add command history or auto-completion
327
328## Running the Client
329
330To run your client with any MCP server:
331
332```bash theme={null}
333uv run client.py path/to/server.py # python server
334uv run client.py path/to/build/index.js # node server
335```
336
337> [!NOTE]
338>
339> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python), your command might look something like this: `python client.py .../quickstart-resources/weather-server-python/weather.py`
340
341The client will:
342
3431. Connect to the specified server
3442. List available tools
3453. Start an interactive chat session where you can:
346 * Enter queries
347 * See tool executions
348 * Get responses from Claude
349
350Here's an example of what it should look like if connected to the weather server from the server quickstart:
351
352
353
354## How It Works
355
356When you submit a query:
357
3581. The client gets the list of available tools from the server
3592. Your query is sent to Claude along with tool descriptions
3603. Claude decides which tools (if any) to use
3614. The client executes any requested tool calls through the server
3625. Results are sent back to Claude
3636. Claude provides a natural language response
3647. The response is displayed to you
365
366## Best practices
367
3681. **Error Handling**
369 * Always wrap tool calls in try-catch blocks
370 * Provide meaningful error messages
371 * Gracefully handle connection issues
372
3732. **Resource Management**
374 * Use `AsyncExitStack` for proper cleanup
375 * Close connections when done
376 * Handle server disconnections
377
3783. **Security**
379 * Store API keys securely in `.env`
380 * Validate server responses
381 * Be cautious with tool permissions
382
3834. **Tool Names**
384 * Tool names can be validated according to the format specified [here](/specification/2025-11-25/server/tools#tool-names)
385 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
386
387## Troubleshooting
388
389### Server Path Issues
390
391* Double-check the path to your server script is correct
392* Use the absolute path if the relative path isn't working
393* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
394* Verify the server file has the correct extension (.py for Python or .js for Node.js)
395
396Example of correct path usage:
397
398```bash theme={null}
399# Relative path
400uv run client.py ./server/weather.py
401
402# Absolute path
403uv run client.py /Users/username/projects/mcp-server/weather.py
404
405# Windows path (either format works)
406uv run client.py C:/projects/mcp-server/weather.py
407uv run client.py C:\\projects\\mcp-server\\weather.py
408```
409
410### Response Timing
411
412* The first response might take up to 30 seconds to return
413* This is normal and happens while:
414 * The server initializes
415 * Claude processes the query
416 * Tools are being executed
417* Subsequent responses are typically faster
418* Don't interrupt the process during this initial waiting period
419
420### Common Error Messages
421
422If you see:
423
424* `FileNotFoundError`: Check your server path
425* `Connection refused`: Ensure the server is running and the path is correct
426* `Tool execution failed`: Verify the tool's required environment variables are set
427* `Timeout error`: Consider increasing the timeout in your client configuration
428
429**TypeScript**
430
431[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-typescript)
432
433## System Requirements
434
435Before starting, ensure your system meets these requirements:
436
437* Mac or Windows computer
438* Node.js 17 or higher installed
439* Latest version of `npm` installed
440* Anthropic API key (Claude)
441
442## Setting Up Your Environment
443
444First, let's create and set up our project:
445
446```bash macOS/Linux theme={null}
447# Create project directory
448mkdir mcp-client-typescript
449cd mcp-client-typescript
450
451# Initialize npm project
452npm init -y
453
454# Install dependencies
455npm install @anthropic-ai/sdk @modelcontextprotocol/sdk dotenv
456
457# Install dev dependencies
458npm install -D @types/node typescript
459
460# Create source file
461touch index.ts
462```
463
464```powershell Windows theme={null}
465# Create project directory
466md mcp-client-typescript
467cd mcp-client-typescript
468
469# Initialize npm project
470npm init -y
471
472# Install dependencies
473npm install @anthropic-ai/sdk @modelcontextprotocol/sdk dotenv
474
475# Install dev dependencies
476npm install -D @types/node typescript
477
478# Create source file
479new-item index.ts
480```
481
482Update your `package.json` to set `type: "module"` and a build script:
483
484```json package.json theme={null}
485{
486 "type": "module",
487 "scripts": {
488 "build": "tsc && chmod 755 build/index.js"
489 }
490}
491```
492
493Create a `tsconfig.json` in the root of your project:
494
495```json tsconfig.json theme={null}
496{
497 "compilerOptions": {
498 "target": "ES2022",
499 "module": "Node16",
500 "moduleResolution": "Node16",
501 "outDir": "./build",
502 "rootDir": "./",
503 "strict": true,
504 "esModuleInterop": true,
505 "skipLibCheck": true,
506 "forceConsistentCasingInFileNames": true
507 },
508 "include": ["index.ts"],
509 "exclude": ["node_modules"]
510}
511```
512
513## Setting Up Your API Key
514
515You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
516
517Create a `.env` file to store it:
518
519```bash theme={null}
520echo "ANTHROPIC_API_KEY=<your key here>" > .env
521```
522
523Add `.env` to your `.gitignore`:
524
525```bash theme={null}
526echo ".env" >> .gitignore
527```
528
529> [!WARNING]
530>
531> Make sure you keep your `ANTHROPIC_API_KEY` secure!
532
533## Creating the Client
534
535### Basic Client Structure
536
537First, let's set up our imports and create the basic client class in `index.ts`:
538
539```typescript theme={null}
540import { Anthropic } from "@anthropic-ai/sdk";
541import {
542 MessageParam,
543 Tool,
544} from "@anthropic-ai/sdk/resources/messages/messages.mjs";
545import { Client } from "@modelcontextprotocol/sdk/client/index.js";
546import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
547import readline from "readline/promises";
548import dotenv from "dotenv";
549
550dotenv.config();
551
552const ANTHROPIC_API_KEY = process.env.ANTHROPIC_API_KEY;
553if (!ANTHROPIC_API_KEY) {
554 throw new Error("ANTHROPIC_API_KEY is not set");
555}
556
557class MCPClient {
558 private mcp: Client;
559 private anthropic: Anthropic;
560 private transport: StdioClientTransport | null = null;
561 private tools: Tool[] = [];
562
563 constructor() {
564 this.anthropic = new Anthropic({
565 apiKey: ANTHROPIC_API_KEY,
566 });
567 this.mcp = new Client({ name: "mcp-client-cli", version: "1.0.0" });
568 }
569 // methods will go here
570}
571```
572
573### Server Connection Management
574
575Next, we'll implement the method to connect to an MCP server:
576
577```typescript theme={null}
578async connectToServer(serverScriptPath: string) {
579 try {
580 const isJs = serverScriptPath.endsWith(".js");
581 const isPy = serverScriptPath.endsWith(".py");
582 if (!isJs && !isPy) {
583 throw new Error("Server script must be a .js or .py file");
584 }
585 const command = isPy
586 ? process.platform === "win32"
587 ? "python"
588 : "python3"
589 : process.execPath;
590
591 this.transport = new StdioClientTransport({
592 command,
593 args: [serverScriptPath],
594 });
595 await this.mcp.connect(this.transport);
596
597 const toolsResult = await this.mcp.listTools();
598 this.tools = toolsResult.tools.map((tool) => {
599 return {
600 name: tool.name,
601 description: tool.description,
602 input_schema: tool.inputSchema,
603 };
604 });
605 console.log(
606 "Connected to server with tools:",
607 this.tools.map(({ name }) => name)
608 );
609 } catch (e) {
610 console.log("Failed to connect to MCP server: ", e);
611 throw e;
612 }
613}
614```
615
616### Query Processing Logic
617
618Now let's add the core functionality for processing queries and handling tool calls:
619
620```typescript theme={null}
621async processQuery(query: string) {
622 const messages: MessageParam[] = [
491623 {
492 "type": "module",
493 "scripts": {
494 "build": "tsc && chmod 755 build/index.js"
495 }
496 }
497 ```
498
499 Create a `tsconfig.json` in the root of your project:
500
501 ```json tsconfig.json theme={null}
502 {
503 "compilerOptions": {
504 "target": "ES2022",
505 "module": "Node16",
506 "moduleResolution": "Node16",
507 "outDir": "./build",
508 "rootDir": "./",
509 "strict": true,
510 "esModuleInterop": true,
511 "skipLibCheck": true,
512 "forceConsistentCasingInFileNames": true
513 },
514 "include": ["index.ts"],
515 "exclude": ["node_modules"]
516 }
517 ```
518
519 ## Setting Up Your API Key
520
521 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
522
523 Create a `.env` file to store it:
524
525 ```bash theme={null}
526 echo "ANTHROPIC_API_KEY=<your key here>" > .env
527 ```
528
529 Add `.env` to your `.gitignore`:
530
531 ```bash theme={null}
532 echo ".env" >> .gitignore
533 ```
534
535 <Warning>
536 Make sure you keep your `ANTHROPIC_API_KEY` secure!
537 </Warning>
538
539 ## Creating the Client
540
541 ### Basic Client Structure
542
543 First, let's set up our imports and create the basic client class in `index.ts`:
544
545 ```typescript theme={null}
546 import { Anthropic } from "@anthropic-ai/sdk";
547 import {
548 MessageParam,
549 Tool,
550 } from "@anthropic-ai/sdk/resources/messages/messages.mjs";
551 import { Client } from "@modelcontextprotocol/sdk/client/index.js";
552 import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
553 import readline from "readline/promises";
554 import dotenv from "dotenv";
555
556 dotenv.config();
557
558 const ANTHROPIC_API_KEY = process.env.ANTHROPIC_API_KEY;
559 if (!ANTHROPIC_API_KEY) {
560 throw new Error("ANTHROPIC_API_KEY is not set");
561 }
562
563 class MCPClient {
564 private mcp: Client;
565 private anthropic: Anthropic;
566 private transport: StdioClientTransport | null = null;
567 private tools: Tool[] = [];
568
569 constructor() {
570 this.anthropic = new Anthropic({
571 apiKey: ANTHROPIC_API_KEY,
572 });
573 this.mcp = new Client({ name: "mcp-client-cli", version: "1.0.0" });
574 }
575 // methods will go here
576 }
577 ```
578
579 ### Server Connection Management
580
581 Next, we'll implement the method to connect to an MCP server:
582
583 ```typescript theme={null}
584 async connectToServer(serverScriptPath: string) {
585 try {
586 const isJs = serverScriptPath.endsWith(".js");
587 const isPy = serverScriptPath.endsWith(".py");
588 if (!isJs && !isPy) {
589 throw new Error("Server script must be a .js or .py file");
590 }
591 const command = isPy
592 ? process.platform === "win32"
593 ? "python"
594 : "python3"
595 : process.execPath;
596
597 this.transport = new StdioClientTransport({
598 command,
599 args: [serverScriptPath],
600 });
601 await this.mcp.connect(this.transport);
602
603 const toolsResult = await this.mcp.listTools();
604 this.tools = toolsResult.tools.map((tool) => {
605 return {
606 name: tool.name,
607 description: tool.description,
608 input_schema: tool.inputSchema,
609 };
610 });
611 console.log(
612 "Connected to server with tools:",
613 this.tools.map(({ name }) => name)
614 );
615 } catch (e) {
616 console.log("Failed to connect to MCP server: ", e);
617 throw e;
618 }
619 }
620 ```
621
622 ### Query Processing Logic
623
624 Now let's add the core functionality for processing queries and handling tool calls:
625
626 ```typescript theme={null}
627 async processQuery(query: string) {
628 const messages: MessageParam[] = [
629 {
630 role: "user",
631 content: query,
632 },
633 ];
624 role: "user",
625 content: query,
626 },
627 ];
628
629 const response = await this.anthropic.messages.create({
630 model: "claude-sonnet-4-20250514",
631 max_tokens: 1000,
632 messages,
633 tools: this.tools,
634 });
635
636 const finalText = [];
637
638 for (const content of response.content) {
639 if (content.type === "text") {
640 finalText.push(content.text);
641 } else if (content.type === "tool_use") {
642 const toolName = content.name;
643 const toolArgs = content.input as { [x: string]: unknown } | undefined;
644
645 const result = await this.mcp.callTool({
646 name: toolName,
647 arguments: toolArgs,
648 });
649 finalText.push(
650 `[Calling tool ${toolName} with args ${JSON.stringify(toolArgs)}]`
651 );
652
653 messages.push({
654 role: "user",
655 content: result.content as string,
656 });
634657
635658 const response = await this.anthropic.messages.create({
636659 model: "claude-sonnet-4-20250514",
637660 max_tokens: 1000,
638661 messages,
639 tools: this.tools,
640662 });
641663
642 const finalText = [];
643
644 for (const content of response.content) {
645 if (content.type === "text") {
646 finalText.push(content.text);
647 } else if (content.type === "tool_use") {
648 const toolName = content.name;
649 const toolArgs = content.input as { [x: string]: unknown } | undefined;
650
651 const result = await this.mcp.callTool({
652 name: toolName,
653 arguments: toolArgs,
654 });
655 finalText.push(
656 `[Calling tool ${toolName} with args ${JSON.stringify(toolArgs)}]`
657 );
658
659 messages.push({
660 role: "user",
661 content: result.content as string,
662 });
663
664 const response = await this.anthropic.messages.create({
665 model: "claude-sonnet-4-20250514",
666 max_tokens: 1000,
667 messages,
668 });
669
670 finalText.push(
671 response.content[0].type === "text" ? response.content[0].text : ""
672 );
673 }
664 finalText.push(
665 response.content[0].type === "text" ? response.content[0].text : ""
666 );
667 }
668 }
669
670 return finalText.join("\n");
671}
672```
673
674### Interactive Chat Interface
675
676Now we'll add the chat loop and cleanup functionality:
677
678```typescript theme={null}
679async chatLoop() {
680 const rl = readline.createInterface({
681 input: process.stdin,
682 output: process.stdout,
683 });
684
685 try {
686 console.log("\nMCP Client Started!");
687 console.log("Type your queries or 'quit' to exit.");
688
689 while (true) {
690 const message = await rl.question("\nQuery: ");
691 if (message.toLowerCase() === "quit") {
692 break;
674693 }
675
676 return finalText.join("\n");
694 const response = await this.processQuery(message);
695 console.log("\n" + response);
677696 }
678 ```
679
680 ### Interactive Chat Interface
681
682 Now we'll add the chat loop and cleanup functionality:
683
684 ```typescript theme={null}
685 async chatLoop() {
686 const rl = readline.createInterface({
687 input: process.stdin,
688 output: process.stdout,
689 });
690
691 try {
692 console.log("\nMCP Client Started!");
693 console.log("Type your queries or 'quit' to exit.");
694
695 while (true) {
696 const message = await rl.question("\nQuery: ");
697 if (message.toLowerCase() === "quit") {
698 break;
699 }
700 const response = await this.processQuery(message);
701 console.log("\n" + response);
702 }
703 } finally {
704 rl.close();
697 } finally {
698 rl.close();
699 }
700}
701
702async cleanup() {
703 await this.mcp.close();
704}
705```
706
707### Main Entry Point
708
709Finally, we'll add the main execution logic:
710
711```typescript theme={null}
712async function main() {
713 if (process.argv.length < 3) {
714 console.log("Usage: node index.ts <path_to_server_script>");
715 return;
716 }
717 const mcpClient = new MCPClient();
718 try {
719 await mcpClient.connectToServer(process.argv[2]);
720 await mcpClient.chatLoop();
721 } catch (e) {
722 console.error("Error:", e);
723 await mcpClient.cleanup();
724 process.exit(1);
725 } finally {
726 await mcpClient.cleanup();
727 process.exit(0);
728 }
729}
730
731main();
732```
733
734## Running the Client
735
736To run your client with any MCP server:
737
738```bash theme={null}
739# Build TypeScript
740npm run build
741
742# Run the client
743node build/index.js path/to/server.py # python server
744node build/index.js path/to/build/index.js # node server
745```
746
747> [!NOTE]
748>
749> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript), your command might look something like this: `node build/index.js .../quickstart-resources/weather-server-typescript/build/index.js`
750
751**The client will:**
752
7531. Connect to the specified server
7542. List available tools
7553. Start an interactive chat session where you can:
756 * Enter queries
757 * See tool executions
758 * Get responses from Claude
759
760## How It Works
761
762When you submit a query:
763
7641. The client gets the list of available tools from the server
7652. Your query is sent to Claude along with tool descriptions
7663. Claude decides which tools (if any) to use
7674. The client executes any requested tool calls through the server
7685. Results are sent back to Claude
7696. Claude provides a natural language response
7707. The response is displayed to you
771
772## Best practices
773
7741. **Error Handling**
775 * Use TypeScript's type system for better error detection
776 * Wrap tool calls in try-catch blocks
777 * Provide meaningful error messages
778 * Gracefully handle connection issues
779
7802. **Security**
781 * Store API keys securely in `.env`
782 * Validate server responses
783 * Be cautious with tool permissions
784
785## Troubleshooting
786
787### Server Path Issues
788
789* Double-check the path to your server script is correct
790* Use the absolute path if the relative path isn't working
791* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
792* Verify the server file has the correct extension (.js for Node.js or .py for Python)
793
794Example of correct path usage:
795
796```bash theme={null}
797# Relative path
798node build/index.js ./server/build/index.js
799
800# Absolute path
801node build/index.js /Users/username/projects/mcp-server/build/index.js
802
803# Windows path (either format works)
804node build/index.js C:/projects/mcp-server/build/index.js
805node build/index.js C:\\projects\\mcp-server\\build\\index.js
806```
807
808### Response Timing
809
810* The first response might take up to 30 seconds to return
811* This is normal and happens while:
812 * The server initializes
813 * Claude processes the query
814 * Tools are being executed
815* Subsequent responses are typically faster
816* Don't interrupt the process during this initial waiting period
817
818### Common Error Messages
819
820If you see:
821
822* `Error: Cannot find module`: Check your build folder and ensure TypeScript compilation succeeded
823* `Connection refused`: Ensure the server is running and the path is correct
824* `Tool execution failed`: Verify the tool's required environment variables are set
825* `ANTHROPIC_API_KEY is not set`: Check your .env file and environment variables
826* `TypeError`: Ensure you're using the correct types for tool arguments
827* `BadRequestError`: Ensure you have enough credits to access the Anthropic API
828
829**Java**
830
831> [!NOTE]
832>
833> This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
834> To learn how to create sync and async MCP Clients manually, consult the [Java SDK Client](https://java.sdk.modelcontextprotocol.io/) documentation
835
836This example demonstrates how to build an interactive chatbot that combines Spring AI's Model Context Protocol (MCP) with the [Brave Search MCP Server](https://github.com/modelcontextprotocol/servers-archived/tree/main/src/brave-search). The application creates a conversational interface powered by Anthropic's Claude AI model that can perform internet searches through Brave Search, enabling natural language interactions with real-time web data.
837[You can find the complete code for this tutorial here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/web-search/brave-chatbot)
838
839## System Requirements
840
841Before starting, ensure your system meets these requirements:
842
843* Java 17 or higher
844* Maven 3.6+
845* npx package manager
846* Anthropic API key (Claude)
847* Brave Search API key
848
849## Setting Up Your Environment
850
8511. Install npx (Node Package eXecute):
852 First, make sure to install [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm)
853 and then run:
854
855 ```bash theme={null}
856 npm install -g npx
857 ```
858
8592. Clone the repository:
860
861 ```bash theme={null}
862 git clone https://github.com/spring-projects/spring-ai-examples.git
863 cd model-context-protocol/web-search/brave-chatbot
864 ```
865
8663. Set up your API keys:
867
868 ```bash theme={null}
869 export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
870 export BRAVE_API_KEY='your-brave-api-key-here'
871 ```
872
8734. Build the application:
874
875 ```bash theme={null}
876 ./mvnw clean install
877 ```
878
8795. Run the application using Maven:
880 ```bash theme={null}
881 ./mvnw spring-boot:run
882 ```
883
884> [!WARNING]
885>
886> Make sure you keep your `ANTHROPIC_API_KEY` and `BRAVE_API_KEY` keys secure!
887
888## How it Works
889
890The application integrates Spring AI with the Brave Search MCP server through several components:
891
892### MCP Client Configuration
893
8941. Required dependencies in pom.xml:
895
896```xml theme={null}
897<dependency>
898 <groupId>org.springframework.ai</groupId>
899 <artifactId>spring-ai-starter-mcp-client</artifactId>
900</dependency>
901<dependency>
902 <groupId>org.springframework.ai</groupId>
903 <artifactId>spring-ai-starter-model-anthropic</artifactId>
904</dependency>
905```
906
9072. Application properties (application.yml):
908
909```yml theme={null}
910spring:
911 ai:
912 mcp:
913 client:
914 enabled: true
915 name: brave-search-client
916 version: 1.0.0
917 type: SYNC
918 request-timeout: 20s
919 stdio:
920 root-change-notification: true
921 servers-configuration: classpath:/mcp-servers-config.json
922 toolcallback:
923 enabled: true
924 anthropic:
925 api-key: ${ANTHROPIC_API_KEY}
926```
927
928This activates the `spring-ai-starter-mcp-client` to create one or more `McpClient`s based on the provided server configuration.
929The `spring.ai.mcp.client.toolcallback.enabled=true` property enables the tool callback mechanism, that automatically registers all MCP tool as spring ai tools.
930It is disabled by default.
931
9323. MCP Server Configuration (`mcp-servers-config.json`):
933
934```json theme={null}
935{
936 "mcpServers": {
937 "brave-search": {
938 "command": "npx",
939 "args": ["-y", "@modelcontextprotocol/server-brave-search"],
940 "env": {
941 "BRAVE_API_KEY": "<PUT YOUR BRAVE API KEY>"
705942 }
706943 }
707
708 async cleanup() {
709 await this.mcp.close();
944 }
945}
946```
947
948### Chat Implementation
949
950The chatbot is implemented using Spring AI's ChatClient with MCP tool integration:
951
952```java theme={null}
953var chatClient = chatClientBuilder
954 .defaultSystem("You are useful assistant, expert in AI and Java.")
955 .defaultToolCallbacks((Object[]) mcpToolAdapter.toolCallbacks())
956 .defaultAdvisors(new MessageChatMemoryAdvisor(new InMemoryChatMemory()))
957 .build();
958```
959
960Key features:
961
962* Uses Claude AI model for natural language understanding
963* Integrates Brave Search through MCP for real-time web search capabilities
964* Maintains conversation memory using InMemoryChatMemory
965* Runs as an interactive command-line application
966
967### Build and run
968
969```bash theme={null}
970./mvnw clean install
971java -jar ./target/ai-mcp-brave-chatbot-0.0.1-SNAPSHOT.jar
972```
973
974or
975
976```bash theme={null}
977./mvnw spring-boot:run
978```
979
980The application will start an interactive chat session where you can ask questions. The chatbot will use Brave Search when it needs to find information from the internet to answer your queries.
981
982The chatbot can:
983
984* Answer questions using its built-in knowledge
985* Perform web searches when needed using Brave Search
986* Remember context from previous messages in the conversation
987* Combine information from multiple sources to provide comprehensive answers
988
989### Advanced Configuration
990
991The MCP client supports additional configuration options:
992
993* Client customization through `McpSyncClientCustomizer` or `McpAsyncClientCustomizer`
994* Multiple clients with multiple transport types: `STDIO` and `SSE` (Server-Sent Events)
995* Integration with Spring AI's tool execution framework
996* Automatic client initialization and lifecycle management
997
998For WebFlux-based applications, you can use the WebFlux starter instead:
999
1000```xml theme={null}
1001<dependency>
1002 <groupId>org.springframework.ai</groupId>
1003 <artifactId>spring-ai-mcp-client-webflux-spring-boot-starter</artifactId>
1004</dependency>
1005```
1006
1007This provides similar functionality but uses a WebFlux-based SSE transport implementation, recommended for production deployments.
1008
1009**Kotlin**
1010
1011[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/kotlin-mcp-client)
1012
1013## System Requirements
1014
1015Before starting, ensure your system meets these requirements:
1016
1017* JDK 11 or higher
1018* Anthropic API key (Claude)
1019
1020## Setting up your environment
1021
1022First, let's install `java` and `gradle` if you haven't already.
1023You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1024Verify your `java` installation:
1025
1026```bash theme={null}
1027java --version
1028```
1029
1030Now, let's create and set up your project:
1031
1032```bash macOS/Linux theme={null}
1033# Create a new directory for our project
1034mkdir kotlin-mcp-client
1035cd kotlin-mcp-client
1036
1037# Initialize a new kotlin project
1038gradle init
1039```
1040
1041```powershell Windows theme={null}
1042# Create a new directory for our project
1043md kotlin-mcp-client
1044cd kotlin-mcp-client
1045# Initialize a new kotlin project
1046gradle init
1047```
1048
1049After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1050
1051Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1052
1053After creating the project, replace the contents of your `build.gradle.kts` with:
1054
1055```kotlin build.gradle.kts theme={null}
1056// Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1057val mcpVersion = "0.9.0"
1058val ktorVersion = "3.2.3"
1059val anthropicVersion = "2.15.0"
1060val slf4jVersion = "2.0.17"
1061
1062plugins {
1063 kotlin("jvm") version "2.3.20"
1064 id("com.gradleup.shadow") version "8.3.9"
1065 application
1066}
1067
1068application {
1069 mainClass.set("MainKt")
1070}
1071
1072dependencies {
1073 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1074 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1075 implementation("com.anthropic:anthropic-java:$anthropicVersion")
1076 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1077}
1078```
1079
1080Verify that everything is set up correctly:
1081
1082```bash theme={null}
1083./gradlew build
1084```
1085
1086## Setting up your API key
1087
1088You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1089
1090Set up your API key:
1091
1092```bash theme={null}
1093export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
1094```
1095
1096> [!WARNING]
1097>
1098> Make sure you keep your `ANTHROPIC_API_KEY` secure!
1099
1100## Creating the Client
1101
1102### Basic Client Structure
1103
1104First, let's create the basic client class:
1105
1106```kotlin theme={null}
1107class MCPClient(apiKey: String) : AutoCloseable {
1108 private val anthropic = AnthropicOkHttpClient.builder()
1109 .apiKey(apiKey)
1110 .build()
1111
1112 private val mcp: Client = Client(
1113 clientInfo = Implementation(name = "mcp-client-cli", version = "1.0.0")
1114 )
1115 private var serverProcess: Process? = null
1116 private lateinit var tools: List<ToolUnion>
1117
1118 // methods will go here
1119
1120 override fun close() {
1121 runBlocking {
1122 mcp.close()
1123 }
1124 serverProcess?.destroy()
1125 anthropic.close()
7101126 }
711 ```
712
713 ### Main Entry Point
714
715 Finally, we'll add the main execution logic:
716
717 ```typescript theme={null}
718 async function main() {
719 if (process.argv.length < 3) {
720 console.log("Usage: node index.ts <path_to_server_script>");
721 return;
722 }
723 const mcpClient = new MCPClient();
724 try {
725 await mcpClient.connectToServer(process.argv[2]);
726 await mcpClient.chatLoop();
727 } catch (e) {
728 console.error("Error:", e);
729 await mcpClient.cleanup();
730 process.exit(1);
731 } finally {
732 await mcpClient.cleanup();
733 process.exit(0);
734 }
1127}
1128```
1129
1130### Server connection management
1131
1132Next, we'll implement the method to connect to an MCP server:
1133
1134```kotlin theme={null}
1135suspend fun connectToServer(serverScriptPath: String) {
1136 val command = buildList {
1137 when (serverScriptPath.substringAfterLast(".")) {
1138 "js" -> add("node")
1139 "py" -> add(if (System.getProperty("os.name").lowercase().contains("win")) "python" else "python3")
1140 "jar" -> addAll(listOf("java", "-jar"))
1141 else -> throw IllegalArgumentException("Server script must be a .js, .py or .jar file")
1142 }
1143 add(serverScriptPath)
7351144 }
7361145
737 main();
738 ```
739
740 ## Running the Client
741
742 To run your client with any MCP server:
743
744 ```bash theme={null}
745 # Build TypeScript
746 npm run build
747
748 # Run the client
749 node build/index.js path/to/server.py # python server
750 node build/index.js path/to/build/index.js # node server
751 ```
752
753 <Note>
754 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript), your command might look something like this: `node build/index.js .../quickstart-resources/weather-server-typescript/build/index.js`
755 </Note>
756
757 **The client will:**
758
759 1. Connect to the specified server
760 2. List available tools
761 3. Start an interactive chat session where you can:
762 * Enter queries
763 * See tool executions
764 * Get responses from Claude
765
766 ## How It Works
767
768 When you submit a query:
769
770 1. The client gets the list of available tools from the server
771 2. Your query is sent to Claude along with tool descriptions
772 3. Claude decides which tools (if any) to use
773 4. The client executes any requested tool calls through the server
774 5. Results are sent back to Claude
775 6. Claude provides a natural language response
776 7. The response is displayed to you
777
778 ## Best practices
779
780 1. **Error Handling**
781 * Use TypeScript's type system for better error detection
782 * Wrap tool calls in try-catch blocks
783 * Provide meaningful error messages
784 * Gracefully handle connection issues
785
786 2. **Security**
787 * Store API keys securely in `.env`
788 * Validate server responses
789 * Be cautious with tool permissions
790
791 ## Troubleshooting
792
793 ### Server Path Issues
794
795 * Double-check the path to your server script is correct
796 * Use the absolute path if the relative path isn't working
797 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
798 * Verify the server file has the correct extension (.js for Node.js or .py for Python)
799
800 Example of correct path usage:
801
802 ```bash theme={null}
803 # Relative path
804 node build/index.js ./server/build/index.js
805
806 # Absolute path
807 node build/index.js /Users/username/projects/mcp-server/build/index.js
808
809 # Windows path (either format works)
810 node build/index.js C:/projects/mcp-server/build/index.js
811 node build/index.js C:\\projects\\mcp-server\\build\\index.js
812 ```
813
814 ### Response Timing
815
816 * The first response might take up to 30 seconds to return
817 * This is normal and happens while:
818 * The server initializes
819 * Claude processes the query
820 * Tools are being executed
821 * Subsequent responses are typically faster
822 * Don't interrupt the process during this initial waiting period
823
824 ### Common Error Messages
825
826 If you see:
827
828 * `Error: Cannot find module`: Check your build folder and ensure TypeScript compilation succeeded
829 * `Connection refused`: Ensure the server is running and the path is correct
830 * `Tool execution failed`: Verify the tool's required environment variables are set
831 * `ANTHROPIC_API_KEY is not set`: Check your .env file and environment variables
832 * `TypeError`: Ensure you're using the correct types for tool arguments
833 * `BadRequestError`: Ensure you have enough credits to access the Anthropic API
834 </Tab>
835
836 <Tab title="Java">
837 <Note>
838 This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
839 To learn how to create sync and async MCP Clients manually, consult the [Java SDK Client](https://java.sdk.modelcontextprotocol.io/) documentation
840 </Note>
841
842 This example demonstrates how to build an interactive chatbot that combines Spring AI's Model Context Protocol (MCP) with the [Brave Search MCP Server](https://github.com/modelcontextprotocol/servers-archived/tree/main/src/brave-search). The application creates a conversational interface powered by Anthropic's Claude AI model that can perform internet searches through Brave Search, enabling natural language interactions with real-time web data.
843 [You can find the complete code for this tutorial here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/web-search/brave-chatbot)
844
845 ## System Requirements
846
847 Before starting, ensure your system meets these requirements:
848
849 * Java 17 or higher
850 * Maven 3.6+
851 * npx package manager
852 * Anthropic API key (Claude)
853 * Brave Search API key
854
855 ## Setting Up Your Environment
856
857 1. Install npx (Node Package eXecute):
858 First, make sure to install [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm)
859 and then run:
860
861 ```bash theme={null}
862 npm install -g npx
863 ```
864
865 2. Clone the repository:
866
867 ```bash theme={null}
868 git clone https://github.com/spring-projects/spring-ai-examples.git
869 cd model-context-protocol/web-search/brave-chatbot
870 ```
871
872 3. Set up your API keys:
873
874 ```bash theme={null}
875 export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
876 export BRAVE_API_KEY='your-brave-api-key-here'
877 ```
878
879 4. Build the application:
880
881 ```bash theme={null}
882 ./mvnw clean install
883 ```
884
885 5. Run the application using Maven:
886 ```bash theme={null}
887 ./mvnw spring-boot:run
888 ```
889
890 <Warning>
891 Make sure you keep your `ANTHROPIC_API_KEY` and `BRAVE_API_KEY` keys secure!
892 </Warning>
893
894 ## How it Works
895
896 The application integrates Spring AI with the Brave Search MCP server through several components:
897
898 ### MCP Client Configuration
899
900 1. Required dependencies in pom.xml:
901
902 ```xml theme={null}
903 <dependency>
904 <groupId>org.springframework.ai</groupId>
905 <artifactId>spring-ai-starter-mcp-client</artifactId>
906 </dependency>
907 <dependency>
908 <groupId>org.springframework.ai</groupId>
909 <artifactId>spring-ai-starter-model-anthropic</artifactId>
910 </dependency>
911 ```
912
913 2. Application properties (application.yml):
914
915 ```yml theme={null}
916 spring:
917 ai:
918 mcp:
919 client:
920 enabled: true
921 name: brave-search-client
922 version: 1.0.0
923 type: SYNC
924 request-timeout: 20s
925 stdio:
926 root-change-notification: true
927 servers-configuration: classpath:/mcp-servers-config.json
928 toolcallback:
929 enabled: true
930 anthropic:
931 api-key: ${ANTHROPIC_API_KEY}
932 ```
933
934 This activates the `spring-ai-starter-mcp-client` to create one or more `McpClient`s based on the provided server configuration.
935 The `spring.ai.mcp.client.toolcallback.enabled=true` property enables the tool callback mechanism, that automatically registers all MCP tool as spring ai tools.
936 It is disabled by default.
937
938 3. MCP Server Configuration (`mcp-servers-config.json`):
939
940 ```json theme={null}
941 {
942 "mcpServers": {
943 "brave-search": {
944 "command": "npx",
945 "args": ["-y", "@modelcontextprotocol/server-brave-search"],
946 "env": {
947 "BRAVE_API_KEY": "<PUT YOUR BRAVE API KEY>"
948 }
949 }
950 }
951 }
952 ```
953
954 ### Chat Implementation
955
956 The chatbot is implemented using Spring AI's ChatClient with MCP tool integration:
957
958 ```java theme={null}
959 var chatClient = chatClientBuilder
960 .defaultSystem("You are useful assistant, expert in AI and Java.")
961 .defaultToolCallbacks((Object[]) mcpToolAdapter.toolCallbacks())
962 .defaultAdvisors(new MessageChatMemoryAdvisor(new InMemoryChatMemory()))
963 .build();
964 ```
965
966 Key features:
967
968 * Uses Claude AI model for natural language understanding
969 * Integrates Brave Search through MCP for real-time web search capabilities
970 * Maintains conversation memory using InMemoryChatMemory
971 * Runs as an interactive command-line application
972
973 ### Build and run
974
975 ```bash theme={null}
976 ./mvnw clean install
977 java -jar ./target/ai-mcp-brave-chatbot-0.0.1-SNAPSHOT.jar
978 ```
979
980 or
981
982 ```bash theme={null}
983 ./mvnw spring-boot:run
984 ```
985
986 The application will start an interactive chat session where you can ask questions. The chatbot will use Brave Search when it needs to find information from the internet to answer your queries.
987
988 The chatbot can:
989
990 * Answer questions using its built-in knowledge
991 * Perform web searches when needed using Brave Search
992 * Remember context from previous messages in the conversation
993 * Combine information from multiple sources to provide comprehensive answers
994
995 ### Advanced Configuration
996
997 The MCP client supports additional configuration options:
998
999 * Client customization through `McpSyncClientCustomizer` or `McpAsyncClientCustomizer`
1000 * Multiple clients with multiple transport types: `STDIO` and `SSE` (Server-Sent Events)
1001 * Integration with Spring AI's tool execution framework
1002 * Automatic client initialization and lifecycle management
1003
1004 For WebFlux-based applications, you can use the WebFlux starter instead:
1005
1006 ```xml theme={null}
1007 <dependency>
1008 <groupId>org.springframework.ai</groupId>
1009 <artifactId>spring-ai-mcp-client-webflux-spring-boot-starter</artifactId>
1010 </dependency>
1011 ```
1012
1013 This provides similar functionality but uses a WebFlux-based SSE transport implementation, recommended for production deployments.
1014 </Tab>
1015
1016 <Tab title="Kotlin">
1017 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/kotlin-mcp-client)
1018
1019 ## System Requirements
1020
1021 Before starting, ensure your system meets these requirements:
1022
1023 * JDK 11 or higher
1024 * Anthropic API key (Claude)
1025
1026 ## Setting up your environment
1027
1028 First, let's install `java` and `gradle` if you haven't already.
1029 You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1030 Verify your `java` installation:
1031
1032 ```bash theme={null}
1033 java --version
1034 ```
1035
1036 Now, let's create and set up your project:
1037
1038 <CodeGroup>
1039 ```bash macOS/Linux theme={null}
1040 # Create a new directory for our project
1041 mkdir kotlin-mcp-client
1042 cd kotlin-mcp-client
1043
1044 # Initialize a new kotlin project
1045 gradle init
1046 ```
1047
1048 ```powershell Windows theme={null}
1049 # Create a new directory for our project
1050 md kotlin-mcp-client
1051 cd kotlin-mcp-client
1052 # Initialize a new kotlin project
1053 gradle init
1054 ```
1055 </CodeGroup>
1056
1057 After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1058
1059 Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1060
1061 After creating the project, replace the contents of your `build.gradle.kts` with:
1062
1063 ```kotlin build.gradle.kts theme={null}
1064 // Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1065 val mcpVersion = "0.9.0"
1066 val ktorVersion = "3.2.3"
1067 val anthropicVersion = "2.15.0"
1068 val slf4jVersion = "2.0.17"
1069
1070 plugins {
1071 kotlin("jvm") version "2.3.20"
1072 id("com.gradleup.shadow") version "8.3.9"
1073 application
1074 }
1075
1076 application {
1077 mainClass.set("MainKt")
1078 }
1079
1080 dependencies {
1081 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1082 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1083 implementation("com.anthropic:anthropic-java:$anthropicVersion")
1084 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1085 }
1086 ```
1087
1088 Verify that everything is set up correctly:
1089
1090 ```bash theme={null}
1091 ./gradlew build
1092 ```
1093
1094 ## Setting up your API key
1095
1096 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1097
1098 Set up your API key:
1099
1100 ```bash theme={null}
1101 export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
1102 ```
1103
1104 <Warning>
1105 Make sure you keep your `ANTHROPIC_API_KEY` secure!
1106 </Warning>
1107
1108 ## Creating the Client
1109
1110 ### Basic Client Structure
1111
1112 First, let's create the basic client class:
1113
1114 ```kotlin theme={null}
1115 class MCPClient(apiKey: String) : AutoCloseable {
1116 private val anthropic = AnthropicOkHttpClient.builder()
1117 .apiKey(apiKey)
1118 .build()
1119
1120 private val mcp: Client = Client(
1121 clientInfo = Implementation(name = "mcp-client-cli", version = "1.0.0")
1122 )
1123 private var serverProcess: Process? = null
1124 private lateinit var tools: List<ToolUnion>
1125
1126 // methods will go here
1127
1128 override fun close() {
1129 runBlocking {
1130 mcp.close()
1131 }
1132 serverProcess?.destroy()
1133 anthropic.close()
1134 }
1135 }
1136 ```
1137
1138 ### Server connection management
1139
1140 Next, we'll implement the method to connect to an MCP server:
1141
1142 ```kotlin theme={null}
1143 suspend fun connectToServer(serverScriptPath: String) {
1144 val command = buildList {
1145 when (serverScriptPath.substringAfterLast(".")) {
1146 "js" -> add("node")
1147 "py" -> add(if (System.getProperty("os.name").lowercase().contains("win")) "python" else "python3")
1148 "jar" -> addAll(listOf("java", "-jar"))
1149 else -> throw IllegalArgumentException("Server script must be a .js, .py or .jar file")
1150 }
1151 add(serverScriptPath)
1152 }
1153
1154 val process = ProcessBuilder(command).start()
1155 serverProcess = process
1156
1157 val transport = StdioClientTransport(
1158 input = process.inputStream.asSource().buffered(),
1159 output = process.outputStream.asSink().buffered(),
1160 )
1161
1162 mcp.connect(transport)
1163
1164 val toolsResult = mcp.listTools()
1165 tools = toolsResult.tools.map { tool ->
1166 ToolUnion.ofTool(
1167 Tool.builder()
1168 .name(tool.name)
1169 .description(tool.description ?: "")
1170 .inputSchema(
1171 Tool.InputSchema.builder()
1172 .type(JsonValue.from(tool.inputSchema.type))
1173 .properties(tool.inputSchema.properties?.toJsonValue() ?: EmptyJsonObject.toJsonValue())
1174 .putAdditionalProperty("required", JsonValue.from(tool.inputSchema.required))
1175 .build(),
1176 )
1177 .build(),
1178 )
1179 }
1180 println("Connected to server with tools: ${tools.joinToString(", ") { it.tool().get().name() }}")
1181 }
1182 ```
1183
1184 <Accordion title="JsonObject.toJsonValue() helper">
1185 This helper converts a kotlinx.serialization `JsonObject` to an Anthropic SDK `JsonValue` using Jackson:
1186
1187 ```kotlin theme={null}
1188 private fun JsonObject.toJsonValue(): JsonValue {
1189 val mapper = ObjectMapper()
1190 val node = mapper.readTree(this.toString())
1191 return JsonValue.fromJsonNode(node)
1192 }
1193 ```
1194 </Accordion>
1195
1196 ### Query processing logic
1197
1198 Now let's add the core functionality for processing queries and handling tool calls:
1199
1200 ```kotlin theme={null}
1201 suspend fun processQuery(query: String): String {
1202 val messages = mutableListOf(
1203 MessageParam.builder()
1204 .role(MessageParam.Role.USER)
1205 .content(query)
1146 val process = ProcessBuilder(command).start()
1147 serverProcess = process
1148
1149 val transport = StdioClientTransport(
1150 input = process.inputStream.asSource().buffered(),
1151 output = process.outputStream.asSink().buffered(),
1152 )
1153
1154 mcp.connect(transport)
1155
1156 val toolsResult = mcp.listTools()
1157 tools = toolsResult.tools.map { tool ->
1158 ToolUnion.ofTool(
1159 Tool.builder()
1160 .name(tool.name)
1161 .description(tool.description ?: "")
1162 .inputSchema(
1163 Tool.InputSchema.builder()
1164 .type(JsonValue.from(tool.inputSchema.type))
1165 .properties(tool.inputSchema.properties?.toJsonValue() ?: EmptyJsonObject.toJsonValue())
1166 .putAdditionalProperty("required", JsonValue.from(tool.inputSchema.required))
1167 .build(),
1168 )
12061169 .build(),
12071170 )
1208
1209 val response = anthropic.messages().create(
1210 MessageCreateParams.builder()
1211 .model("claude-sonnet-4-20250514")
1212 .maxTokens(1024)
1213 .messages(messages)
1214 .tools(tools)
1215 .build(),
1216 )
1217
1218 val finalText = mutableListOf<String>()
1219 response.content().forEach { content ->
1220 when {
1221 content.isText() -> finalText.add(content.text().get().text())
1222
1223 content.isToolUse() -> {
1224 val toolName = content.toolUse().get().name()
1225 val toolArgs =
1226 content.toolUse().get()._input().convert(object : TypeReference<Map<String, JsonValue>>() {})
1227
1228 val result = mcp.callTool(
1229 name = toolName,
1230 arguments = toolArgs ?: emptyMap(),
1231 )
1232 finalText.add("[Calling tool $toolName with args $toolArgs]")
1233
1234 messages.add(
1235 MessageParam.builder()
1236 .role(MessageParam.Role.USER)
1237 .content(
1238 result.content
1239 .filterIsInstance<TextContent>()
1240 .joinToString("\n") { it.text }
1241 )
1242 .build(),
1243 )
1244
1245 val aiResponse = anthropic.messages().create(
1246 MessageCreateParams.builder()
1247 .model("claude-sonnet-4-20250514")
1248 .maxTokens(1024)
1249 .messages(messages)
1250 .build(),
1251 )
1252
1253 finalText.add(aiResponse.content().first().text().get().text())
1254 }
1255 }
1256 }
1257
1258 return finalText.joinToString("\n")
12591171 }
1260 ```
1261
1262 ### Interactive chat
1263
1264 We'll add the chat loop:
1265
1266 ```kotlin theme={null}
1267 suspend fun chatLoop() {
1268 println("\nMCP Client Started!")
1269 println("Type your queries or 'quit' to exit.")
1270
1271 while (true) {
1272 print("\nQuery: ")
1273 val message = readlnOrNull() ?: break
1274 if (message.trim().lowercase() == "quit") break
1275
1276 try {
1277 val response = processQuery(message)
1278 println("\n$response")
1279 } catch (e: Exception) {
1280 println("\nError: ${e.message}")
1172 println("Connected to server with tools: ${tools.joinToString(", ") { it.tool().get().name() }}")
1173}
1174```
1175
1176> **JsonObject.toJsonValue() helper**
1177>
1178> This helper converts a kotlinx.serialization `JsonObject` to an Anthropic SDK `JsonValue` using Jackson:
1179>
1180> ```kotlin theme={null}
1181> private fun JsonObject.toJsonValue(): JsonValue {
1182> val mapper = ObjectMapper()
1183> val node = mapper.readTree(this.toString())
1184> return JsonValue.fromJsonNode(node)
1185> }
1186> ```
1187
1188### Query processing logic
1189
1190Now let's add the core functionality for processing queries and handling tool calls:
1191
1192```kotlin theme={null}
1193suspend fun processQuery(query: String): String {
1194 val messages = mutableListOf(
1195 MessageParam.builder()
1196 .role(MessageParam.Role.USER)
1197 .content(query)
1198 .build(),
1199 )
1200
1201 val response = anthropic.messages().create(
1202 MessageCreateParams.builder()
1203 .model("claude-sonnet-4-20250514")
1204 .maxTokens(1024)
1205 .messages(messages)
1206 .tools(tools)
1207 .build(),
1208 )
1209
1210 val finalText = mutableListOf<String>()
1211 response.content().forEach { content ->
1212 when {
1213 content.isText() -> finalText.add(content.text().get().text())
1214
1215 content.isToolUse() -> {
1216 val toolName = content.toolUse().get().name()
1217 val toolArgs =
1218 content.toolUse().get()._input().convert(object : TypeReference<Map<String, JsonValue>>() {})
1219
1220 val result = mcp.callTool(
1221 name = toolName,
1222 arguments = toolArgs ?: emptyMap(),
1223 )
1224 finalText.add("[Calling tool $toolName with args $toolArgs]")
1225
1226 messages.add(
1227 MessageParam.builder()
1228 .role(MessageParam.Role.USER)
1229 .content(
1230 result.content
1231 .filterIsInstance<TextContent>()
1232 .joinToString("\n") { it.text }
1233 )
1234 .build(),
1235 )
1236
1237 val aiResponse = anthropic.messages().create(
1238 MessageCreateParams.builder()
1239 .model("claude-sonnet-4-20250514")
1240 .maxTokens(1024)
1241 .messages(messages)
1242 .build(),
1243 )
1244
1245 finalText.add(aiResponse.content().first().text().get().text())
12811246 }
12821247 }
12831248 }
1284 ```
1285
1286 ### Main entry point
1287
1288 Finally, we'll add the main execution function:
1289
1290 ```kotlin theme={null}
1291 fun main(args: Array<String>) = runBlocking {
1292 require(args.isNotEmpty()) { "Usage: java -jar <path> <path_to_server_script>" }
1293
1294 val apiKey = System.getenv("ANTHROPIC_API_KEY")
1295 require(!apiKey.isNullOrBlank()) { "ANTHROPIC_API_KEY environment variable is not set" }
1296
1297 val client = MCPClient(apiKey)
1298 client.use {
1299 client.connectToServer(args.first())
1300 client.chatLoop()
1249
1250 return finalText.joinToString("\n")
1251}
1252```
1253
1254### Interactive chat
1255
1256We'll add the chat loop:
1257
1258```kotlin theme={null}
1259suspend fun chatLoop() {
1260 println("\nMCP Client Started!")
1261 println("Type your queries or 'quit' to exit.")
1262
1263 while (true) {
1264 print("\nQuery: ")
1265 val message = readlnOrNull() ?: break
1266 if (message.trim().lowercase() == "quit") break
1267
1268 try {
1269 val response = processQuery(message)
1270 println("\n$response")
1271 } catch (e: Exception) {
1272 println("\nError: ${e.message}")
13011273 }
13021274 }
1303 ```
1304
1305 ## Running the client
1306
1307 To run your client with any MCP server:
1308
1309 ```bash theme={null}
1310 ./gradlew build
1311
1312 # Run the client
1313 java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.jar # JVM server
1314 java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.py # Python server
1315 java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/build/index.js # Node server
1316 ```
1317
1318 Alternatively, you can run directly with Gradle:
1319
1320 ```bash theme={null}
1321 ./gradlew run --args="path/to/server.jar"
1322 ```
1323
1324 <Note>
1325 If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar .../samples/weather-stdio-server/build/libs/weather-stdio-server-0.1.0-all.jar`
1326 </Note>
1327
1328 **The client will:**
1329
1330 1. Connect to the specified server
1331 2. List available tools
1332 3. Start an interactive chat session where you can:
1333 * Enter queries
1334 * See tool executions
1335 * Get responses from Claude
1336
1337 ## How it works
1338
1339 Here's a high-level workflow schema:
1340
1341 ```mermaid theme={null}
1342 ---
1343 config:
1344 theme: neutral
1345 ---
1346 sequenceDiagram
1347 actor User
1348 participant Client
1349 participant Claude
1350 participant MCP_Server as MCP Server
1351 participant Tools
1352
1353 User->>Client: Send query
1354 Client<<->>MCP_Server: Get available tools
1355 Client->>Claude: Send query with tool descriptions
1356 Claude-->>Client: Decide tool execution
1357 Client->>MCP_Server: Request tool execution
1358 MCP_Server->>Tools: Execute chosen tools
1359 Tools-->>MCP_Server: Return results
1360 MCP_Server-->>Client: Send results
1361 Client->>Claude: Send tool results
1362 Claude-->>Client: Provide final response
1363 Client-->>User: Display response
1364 ```
1365
1366 When you submit a query:
1367
1368 1. The client gets the list of available tools from the server
1369 2. Your query is sent to Claude along with tool descriptions
1370 3. Claude decides which tools (if any) to use
1371 4. The client executes any requested tool calls through the server
1372 5. Results are sent back to Claude
1373 6. Claude provides a natural language response
1374 7. The response is displayed to you
1375
1376 ## Best practices
1377
1378 1. **Error Handling**
1379 * Leverage Kotlin's type system to model errors explicitly
1380 * Wrap external tool and API calls in `try-catch` blocks when exceptions are possible
1381 * Provide clear and meaningful error messages
1382 * Handle network timeouts and connection issues gracefully
1383
1384 2. **Security**
1385 * Store API keys and secrets securely in `local.properties`, environment variables, or secret managers
1386 * Validate all external responses to avoid unexpected or unsafe data usage
1387 * Be cautious with permissions and trust boundaries when using tools
1388
1389 3. **Environment**
1390 * Set `ANTHROPIC_API_KEY` through environment variables rather than hardcoding
1391 * Use `.env` files with appropriate `.gitignore` rules for local development
1392
1393 ## Troubleshooting
1394
1395 ### Server Path Issues
1396
1397 * Double-check the path to your server script is correct
1398 * Use the absolute path if the relative path isn't working
1399 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
1400 * Make sure that the required runtime is installed (java for Java, npm for Node.js, or uv for Python)
1401 * Verify the server file has the correct extension (.jar for Java, .js for Node.js or .py for Python)
1402
1403 Example of correct path usage:
1404
1405 ```bash theme={null}
1406 # Relative path
1407 java -jar build/libs/client.jar ./server/build/libs/server.jar
1408
1409 # Absolute path
1410 java -jar build/libs/client.jar /Users/username/projects/mcp-server/build/libs/server.jar
1411
1412 # Windows path (either format works)
1413 java -jar build/libs/client.jar C:/projects/mcp-server/build/libs/server.jar
1414 java -jar build/libs/client.jar C:\\projects\\mcp-server\\build\\libs\\server.jar
1415 ```
1416
1417 ### Build Issues
1418
1419 * Use `./gradlew build` or `./gradlew shadowJar` (not `./gradlew jar`) to create the shadow JAR with all dependencies
1420 * If you get JDK version errors, ensure your installed JDK version matches or exceeds the `jvmToolchain` setting in `build.gradle.kts`
1421
1422 ### Response Timing
1423
1424 * The first response might take up to 30 seconds to return
1425 * This is normal and happens while:
1426 * The server initializes
1427 * Claude processes the query
1428 * Tools are being executed
1429 * Subsequent responses are typically faster
1430 * Don't interrupt the process during this initial waiting period
1431
1432 ### Common Error Messages
1433
1434 If you see:
1435
1436 * `Connection refused`: Ensure the server is running and the path is correct
1437 * `Tool execution failed`: Verify the tool's required environment variables are set
1438 * `ANTHROPIC_API_KEY is not set`: Check your environment variables
1439 </Tab>
1440
1441 <Tab title="C#">
1442 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartClient)
1443
1444 ## System Requirements
1445
1446 Before starting, ensure your system meets these requirements:
1447
1448 * .NET 8.0 or higher
1449 * Anthropic API key (Claude)
1450 * Windows, Linux, or macOS
1451
1452 ## Setting up your environment
1453
1454 First, create a new .NET project:
1455
1456 ```bash theme={null}
1457 dotnet new console -n QuickstartClient
1458 cd QuickstartClient
1459 ```
1460
1461 Then, add the required dependencies to your project:
1462
1463 ```bash theme={null}
1464 dotnet add package ModelContextProtocol --prerelease
1465 dotnet add package Anthropic.SDK
1466 dotnet add package Microsoft.Extensions.Hosting
1467 dotnet add package Microsoft.Extensions.AI
1468 ```
1469
1470 ## Setting up your API key
1471
1472 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1473
1474 ```bash theme={null}
1475 dotnet user-secrets init
1476 dotnet user-secrets set "ANTHROPIC_API_KEY" "<your key here>"
1477 ```
1478
1479 ## Creating the Client
1480
1481 ### Basic Client Structure
1482
1483 First, let's setup the basic client class in the file `Program.cs`:
1484
1485 ```csharp theme={null}
1486 using Anthropic.SDK;
1487 using Microsoft.Extensions.AI;
1488 using Microsoft.Extensions.Configuration;
1489 using Microsoft.Extensions.Hosting;
1490 using ModelContextProtocol.Client;
1491 using ModelContextProtocol.Protocol.Transport;
1492
1493 var builder = Host.CreateApplicationBuilder(args);
1494
1495 builder.Configuration
1496 .AddEnvironmentVariables()
1497 .AddUserSecrets<Program>();
1498 ```
1499
1500 This creates the beginnings of a .NET console application that can read the API key from user secrets.
1501
1502 Next, we'll setup the MCP Client:
1503
1504 ```csharp theme={null}
1505 var (command, arguments) = GetCommandAndArguments(args);
1506
1507 var clientTransport = new StdioClientTransport(new()
1275}
1276```
1277
1278### Main entry point
1279
1280Finally, we'll add the main execution function:
1281
1282```kotlin theme={null}
1283fun main(args: Array<String>) = runBlocking {
1284 require(args.isNotEmpty()) { "Usage: java -jar <path> <path_to_server_script>" }
1285
1286 val apiKey = System.getenv("ANTHROPIC_API_KEY")
1287 require(!apiKey.isNullOrBlank()) { "ANTHROPIC_API_KEY environment variable is not set" }
1288
1289 val client = MCPClient(apiKey)
1290 client.use {
1291 client.connectToServer(args.first())
1292 client.chatLoop()
1293 }
1294}
1295```
1296
1297## Running the client
1298
1299To run your client with any MCP server:
1300
1301```bash theme={null}
1302./gradlew build
1303
1304# Run the client
1305java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.jar # JVM server
1306java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.py # Python server
1307java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/build/index.js # Node server
1308```
1309
1310Alternatively, you can run directly with Gradle:
1311
1312```bash theme={null}
1313./gradlew run --args="path/to/server.jar"
1314```
1315
1316> [!NOTE]
1317>
1318> If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar .../samples/weather-stdio-server/build/libs/weather-stdio-server-0.1.0-all.jar`
1319
1320**The client will:**
1321
13221. Connect to the specified server
13232. List available tools
13243. Start an interactive chat session where you can:
1325 * Enter queries
1326 * See tool executions
1327 * Get responses from Claude
1328
1329## How it works
1330
1331Here's a high-level workflow schema:
1332
1333```mermaid theme={null}
1334---
1335config:
1336 theme: neutral
1337---
1338sequenceDiagram
1339 actor User
1340 participant Client
1341 participant Claude
1342 participant MCP_Server as MCP Server
1343 participant Tools
1344
1345 User->>Client: Send query
1346 Client<<->>MCP_Server: Get available tools
1347 Client->>Claude: Send query with tool descriptions
1348 Claude-->>Client: Decide tool execution
1349 Client->>MCP_Server: Request tool execution
1350 MCP_Server->>Tools: Execute chosen tools
1351 Tools-->>MCP_Server: Return results
1352 MCP_Server-->>Client: Send results
1353 Client->>Claude: Send tool results
1354 Claude-->>Client: Provide final response
1355 Client-->>User: Display response
1356```
1357
1358When you submit a query:
1359
13601. The client gets the list of available tools from the server
13612. Your query is sent to Claude along with tool descriptions
13623. Claude decides which tools (if any) to use
13634. The client executes any requested tool calls through the server
13645. Results are sent back to Claude
13656. Claude provides a natural language response
13667. The response is displayed to you
1367
1368## Best practices
1369
13701. **Error Handling**
1371 * Leverage Kotlin's type system to model errors explicitly
1372 * Wrap external tool and API calls in `try-catch` blocks when exceptions are possible
1373 * Provide clear and meaningful error messages
1374 * Handle network timeouts and connection issues gracefully
1375
13762. **Security**
1377 * Store API keys and secrets securely in `local.properties`, environment variables, or secret managers
1378 * Validate all external responses to avoid unexpected or unsafe data usage
1379 * Be cautious with permissions and trust boundaries when using tools
1380
13813. **Environment**
1382 * Set `ANTHROPIC_API_KEY` through environment variables rather than hardcoding
1383 * Use `.env` files with appropriate `.gitignore` rules for local development
1384
1385## Troubleshooting
1386
1387### Server Path Issues
1388
1389* Double-check the path to your server script is correct
1390* Use the absolute path if the relative path isn't working
1391* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
1392* Make sure that the required runtime is installed (java for Java, npm for Node.js, or uv for Python)
1393* Verify the server file has the correct extension (.jar for Java, .js for Node.js or .py for Python)
1394
1395Example of correct path usage:
1396
1397```bash theme={null}
1398# Relative path
1399java -jar build/libs/client.jar ./server/build/libs/server.jar
1400
1401# Absolute path
1402java -jar build/libs/client.jar /Users/username/projects/mcp-server/build/libs/server.jar
1403
1404# Windows path (either format works)
1405java -jar build/libs/client.jar C:/projects/mcp-server/build/libs/server.jar
1406java -jar build/libs/client.jar C:\\projects\\mcp-server\\build\\libs\\server.jar
1407```
1408
1409### Build Issues
1410
1411* Use `./gradlew build` or `./gradlew shadowJar` (not `./gradlew jar`) to create the shadow JAR with all dependencies
1412* If you get JDK version errors, ensure your installed JDK version matches or exceeds the `jvmToolchain` setting in `build.gradle.kts`
1413
1414### Response Timing
1415
1416* The first response might take up to 30 seconds to return
1417* This is normal and happens while:
1418 * The server initializes
1419 * Claude processes the query
1420 * Tools are being executed
1421* Subsequent responses are typically faster
1422* Don't interrupt the process during this initial waiting period
1423
1424### Common Error Messages
1425
1426If you see:
1427
1428* `Connection refused`: Ensure the server is running and the path is correct
1429* `Tool execution failed`: Verify the tool's required environment variables are set
1430* `ANTHROPIC_API_KEY is not set`: Check your environment variables
1431
1432**C#**
1433
1434[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartClient)
1435
1436## System Requirements
1437
1438Before starting, ensure your system meets these requirements:
1439
1440* .NET 8.0 or higher
1441* Anthropic API key (Claude)
1442* Windows, Linux, or macOS
1443
1444## Setting up your environment
1445
1446First, create a new .NET project:
1447
1448```bash theme={null}
1449dotnet new console -n QuickstartClient
1450cd QuickstartClient
1451```
1452
1453Then, add the required dependencies to your project:
1454
1455```bash theme={null}
1456dotnet add package ModelContextProtocol --prerelease
1457dotnet add package Anthropic.SDK
1458dotnet add package Microsoft.Extensions.Hosting
1459dotnet add package Microsoft.Extensions.AI
1460```
1461
1462## Setting up your API key
1463
1464You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1465
1466```bash theme={null}
1467dotnet user-secrets init
1468dotnet user-secrets set "ANTHROPIC_API_KEY" "<your key here>"
1469```
1470
1471## Creating the Client
1472
1473### Basic Client Structure
1474
1475First, let's setup the basic client class in the file `Program.cs`:
1476
1477```csharp theme={null}
1478using Anthropic.SDK;
1479using Microsoft.Extensions.AI;
1480using Microsoft.Extensions.Configuration;
1481using Microsoft.Extensions.Hosting;
1482using ModelContextProtocol.Client;
1483using ModelContextProtocol.Protocol.Transport;
1484
1485var builder = Host.CreateApplicationBuilder(args);
1486
1487builder.Configuration
1488 .AddEnvironmentVariables()
1489 .AddUserSecrets<Program>();
1490```
1491
1492This creates the beginnings of a .NET console application that can read the API key from user secrets.
1493
1494Next, we'll setup the MCP Client:
1495
1496```csharp theme={null}
1497var (command, arguments) = GetCommandAndArguments(args);
1498
1499var clientTransport = new StdioClientTransport(new()
1500{
1501 Name = "Demo Server",
1502 Command = command,
1503 Arguments = arguments,
1504});
1505
1506await using var mcpClient = await McpClient.CreateAsync(clientTransport);
1507
1508var tools = await mcpClient.ListToolsAsync();
1509foreach (var tool in tools)
1510{
1511 Console.WriteLine($"Connected to server with tools: {tool.Name}");
1512}
1513```
1514
1515Add this function at the end of the `Program.cs` file:
1516
1517```csharp theme={null}
1518static (string command, string[] arguments) GetCommandAndArguments(string[] args)
1519{
1520 return args switch
15081521 {
1509 Name = "Demo Server",
1510 Command = command,
1511 Arguments = arguments,
1512 });
1513
1514 await using var mcpClient = await McpClient.CreateAsync(clientTransport);
1515
1516 var tools = await mcpClient.ListToolsAsync();
1517 foreach (var tool in tools)
1522 [var script] when script.EndsWith(".py") => ("python", args),
1523 [var script] when script.EndsWith(".js") => ("node", args),
1524 [var script] when Directory.Exists(script) || (File.Exists(script) && script.EndsWith(".csproj")) => ("dotnet", ["run", "--project", script, "--no-build"]),
1525 _ => throw new NotSupportedException("An unsupported server script was provided. Supported scripts are .py, .js, or .csproj")
1526 };
1527}
1528```
1529
1530This creates an MCP client that will connect to a server that is provided as a command line argument. It then lists the available tools from the connected server.
1531
1532### Query processing logic
1533
1534Now let's add the core functionality for processing queries and handling tool calls:
1535
1536```csharp theme={null}
1537using var anthropicClient = new AnthropicClient(new APIAuthentication(builder.Configuration["ANTHROPIC_API_KEY"]))
1538 .Messages
1539 .AsBuilder()
1540 .UseFunctionInvocation()
1541 .Build();
1542
1543var options = new ChatOptions
1544{
1545 MaxOutputTokens = 1000,
1546 ModelId = "claude-sonnet-4-20250514",
1547 Tools = [.. tools]
1548};
1549
1550Console.ForegroundColor = ConsoleColor.Green;
1551Console.WriteLine("MCP Client Started!");
1552Console.ResetColor();
1553
1554PromptForInput();
1555while(Console.ReadLine() is string query && !"exit".Equals(query, StringComparison.OrdinalIgnoreCase))
1556{
1557 if (string.IsNullOrWhiteSpace(query))
15181558 {
1519 Console.WriteLine($"Connected to server with tools: {tool.Name}");
1559 PromptForInput();
1560 continue;
15201561 }
1521 ```
1522
1523 Add this function at the end of the `Program.cs` file:
1524
1525 ```csharp theme={null}
1526 static (string command, string[] arguments) GetCommandAndArguments(string[] args)
1562
1563 await foreach (var message in anthropicClient.GetStreamingResponseAsync(query, options))
15271564 {
1528 return args switch
1529 {
1530 [var script] when script.EndsWith(".py") => ("python", args),
1531 [var script] when script.EndsWith(".js") => ("node", args),
1532 [var script] when Directory.Exists(script) || (File.Exists(script) && script.EndsWith(".csproj")) => ("dotnet", ["run", "--project", script, "--no-build"]),
1533 _ => throw new NotSupportedException("An unsupported server script was provided. Supported scripts are .py, .js, or .csproj")
1534 };
1565 Console.Write(message);
15351566 }
1536 ```
1537
1538 This creates an MCP client that will connect to a server that is provided as a command line argument. It then lists the available tools from the connected server.
1539
1540 ### Query processing logic
1541
1542 Now let's add the core functionality for processing queries and handling tool calls:
1543
1544 ```csharp theme={null}
1545 using var anthropicClient = new AnthropicClient(new APIAuthentication(builder.Configuration["ANTHROPIC_API_KEY"]))
1546 .Messages
1547 .AsBuilder()
1548 .UseFunctionInvocation()
1549 .Build();
1550
1551 var options = new ChatOptions
1552 {
1553 MaxOutputTokens = 1000,
1554 ModelId = "claude-sonnet-4-20250514",
1555 Tools = [.. tools]
1556 };
1557
1558 Console.ForegroundColor = ConsoleColor.Green;
1559 Console.WriteLine("MCP Client Started!");
1567 Console.WriteLine();
1568
1569 PromptForInput();
1570}
1571
1572static void PromptForInput()
1573{
1574 Console.WriteLine("Enter a command (or 'exit' to quit):");
1575 Console.ForegroundColor = ConsoleColor.Cyan;
1576 Console.Write("> ");
15601577 Console.ResetColor();
1561
1562 PromptForInput();
1563 while(Console.ReadLine() is string query && !"exit".Equals(query, StringComparison.OrdinalIgnoreCase))
1564 {
1565 if (string.IsNullOrWhiteSpace(query))
1566 {
1567 PromptForInput();
1568 continue;
1569 }
1570
1571 await foreach (var message in anthropicClient.GetStreamingResponseAsync(query, options))
1572 {
1573 Console.Write(message);
1574 }
1575 Console.WriteLine();
1576
1577 PromptForInput();
1578 }
1579
1580 static void PromptForInput()
1581 {
1582 Console.WriteLine("Enter a command (or 'exit' to quit):");
1583 Console.ForegroundColor = ConsoleColor.Cyan;
1584 Console.Write("> ");
1585 Console.ResetColor();
1586 }
1587 ```
1588
1589 ## Key Components Explained
1590
1591 ### 1. Client Initialization
1592
1593 * The client is initialized using `McpClient.CreateAsync()`, which sets up the transport type and command to run the server.
1594
1595 ### 2. Server Connection
1596
1597 * Supports Python, Node.js, and .NET servers.
1598 * The server is started using the command specified in the arguments.
1599 * Configures to use stdio for communication with the server.
1600 * Initializes the session and available tools.
1601
1602 ### 3. Query Processing
1603
1604 * Leverages [Microsoft.Extensions.AI](https://learn.microsoft.com/dotnet/ai/ai-extensions) for the chat client.
1605 * Configures the `IChatClient` to use automatic tool (function) invocation.
1606 * The client reads user input and sends it to the server.
1607 * The server processes the query and returns a response.
1608 * The response is displayed to the user.
1609
1610 ## Running the Client
1611
1612 To run your client with any MCP server:
1613
1614 ```bash theme={null}
1615 dotnet run -- path/to/server.csproj # dotnet server
1616 dotnet run -- path/to/server.py # python server
1617 dotnet run -- path/to/server.js # node server
1618 ```
1619
1620 <Note>
1621 If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `dotnet run -- path/to/QuickstartWeatherServer`.
1622 </Note>
1623
1624 The client will:
1625
1626 1. Connect to the specified server
1627 2. List available tools
1628 3. Start an interactive chat session where you can:
1629 * Enter queries
1630 * See tool executions
1631 * Get responses from Claude
1632 4. Exit the session when done
1633
1634 Here's an example of what it should look like if connected to the weather server quickstart:
1635
1636 <Frame>
1637 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-dotnet-client.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=fcf28dde150d6db879402ad8150c6b23" width="1115" height="666" data-path="images/quickstart-dotnet-client.png" />
1638 </Frame>
1639 </Tab>
1640
1641 <Tab title="Ruby">
1642 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-ruby)
1643
1644 ## System Requirements
1645
1646 Before starting, ensure your system meets these requirements:
1647
1648 * Mac or Windows computer
1649 * Ruby 3.2.0 or higher installed (required by the [Anthropic SDK](https://github.com/anthropics/anthropic-sdk-ruby))
1650 * Anthropic API key (Claude)
1651
1652 ## Setting Up Your Environment
1653
1654 First, create a new Ruby project:
1655
1656 <CodeGroup>
1657 ```bash macOS/Linux theme={null}
1658 # Create project directory
1659 mkdir mcp-client
1660 cd mcp-client
1661
1662 # Create a Gemfile
1663 bundle init
1664
1665 # Add required dependencies
1666 bundle add anthropic base64 dotenv mcp
1667
1668 # Create our main file
1669 touch client.rb
1670 ```
1671
1672 ```powershell Windows theme={null}
1673 # Create project directory
1674 mkdir mcp-client
1675 cd mcp-client
1676
1677 # Create a Gemfile
1678 bundle init
1679
1680 # Add required dependencies
1681 bundle add anthropic base64 dotenv mcp
1682
1683 # Create our main file
1684 new-item client.rb
1685 ```
1686 </CodeGroup>
1687
1688 ## Setting Up Your API Key
1689
1690 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1691
1692 Create a `.env` file to store it:
1693
1694 ```bash theme={null}
1695 echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
1696 ```
1697
1698 Add `.env` to your `.gitignore`:
1699
1700 ```bash theme={null}
1701 echo ".env" >> .gitignore
1702 ```
1703
1704 <Warning>
1705 Make sure you keep your `ANTHROPIC_API_KEY` secure!
1706 </Warning>
1707
1708 ## Creating the Client
1709
1710 ### Basic Client Structure
1711
1712 First, let's set up our requires and create the basic client class:
1713
1714 ```ruby theme={null}
1715 require "anthropic"
1716 require "dotenv/load"
1717 require "json"
1718 require "mcp"
1719
1720 class MCPClient
1721 ANTHROPIC_MODEL = "claude-sonnet-4-20250514"
1722
1723 def initialize
1724 @mcp_client = nil
1725 @transport = nil
1726 @anthropic_client = nil
1727 end
1728
1729 # methods will go here
1730 end
1731 ```
1732
1733 ### Server Connection Management
1734
1735 Next, we'll implement the method to connect to an MCP server:
1736
1737 ```ruby theme={null}
1738 def connect_to_server(server_script_path)
1739 command = case File.extname(server_script_path)
1740 when ".rb"
1741 "ruby"
1742 when ".py"
1743 "python3"
1744 when ".js"
1745 "node"
1746 else
1747 raise ArgumentError, "Server script must be a .rb, .py, or .js file."
1748 end
1749
1750 @transport = MCP::Client::Stdio.new(command: command, args: [server_script_path])
1751 @mcp_client = MCP::Client.new(transport: @transport)
1752 @mcp_client.connect
1753
1754 tool_names = @mcp_client.tools.map(&:name)
1755 puts "\nConnected to server with tools: #{tool_names}"
1756 end
1757 ```
1758
1759 ### Query Processing Logic
1760
1761 Now let's add the core functionality for processing queries and handling tool calls:
1762
1763 ```ruby theme={null}
1764 private
1765
1766 def process_query(query)
1767 messages = [{ role: "user", content: query }]
1768
1769 available_tools = @mcp_client.tools.map do |tool|
1770 { name: tool.name, description: tool.description, input_schema: tool.input_schema }
1771 end
1772
1773 # Initial Claude API call.
1774 response = chat(messages, tools: available_tools)
1775
1776 # Process response and handle tool calls.
1777 if response.content.any?(Anthropic::Models::ToolUseBlock)
1778 assistant_content = response.content.filter_map do |content_block|
1779 case content_block
1780 when Anthropic::Models::TextBlock
1781 { type: "text", text: content_block.text }
1782 when Anthropic::Models::ToolUseBlock
1783 { type: "tool_use", id: content_block.id, name: content_block.name, input: content_block.input }
1784 end
1785 end
1786 messages << { role: "assistant", content: assistant_content }
1787 end
1788
1789 response.content.each_with_object([]) do |content, response_parts|
1790 case content
1791 when Anthropic::Models::TextBlock
1792 response_parts << content.text
1793 when Anthropic::Models::ToolUseBlock
1794 # Execute tool call via MCP.
1795 result = @mcp_client.call_tool(name: content.name, arguments: content.input)
1796 response_parts << "[Calling tool #{content.name} with args #{content.input.to_json}]"
1797
1798 tool_result_content = result.dig("result", "content")
1799 result_text = if tool_result_content.is_a?(Array)
1800 tool_result_content.filter_map { |content_item| content_item["text"] }.join("\n")
1801 else
1802 tool_result_content.to_s
1803 end
1804
1805 messages << {
1806 role: "user",
1807 content: [{
1808 type: "tool_result",
1809 tool_use_id: content.id,
1810 content: result_text
1811 }]
1812 }
1813
1814 # Get next response from Claude.
1815 response = chat(messages)
1816
1817 response.content.each do |content_block|
1818 response_parts << content_block.text if content_block.is_a?(Anthropic::Models::TextBlock)
1819 end
1820 end
1821 end.join("\n")
1822 end
1823
1824 def chat(messages, tools: nil)
1825 params = { model: ANTHROPIC_MODEL, max_tokens: 1000, messages: messages }
1826 params[:tools] = tools if tools
1827
1828 anthropic_client.messages.create(**params)
1829 end
1830
1831 def anthropic_client
1832 @anthropic_client ||= Anthropic::Client.new(api_key: ENV["ANTHROPIC_API_KEY"])
1833 end
1834 ```
1835
1836 ### Interactive Chat Interface
1837
1838 Now we'll add the chat loop and cleanup functionality:
1839
1840 ```ruby theme={null}
1841 def chat_loop
1842 puts <<~MESSAGE
1843 MCP Client Started!
1844 Type your queries or 'quit' to exit.
1845 MESSAGE
1846
1847 loop do
1848 print "\nQuery: "
1849 line = $stdin.gets
1850 break if line.nil?
1851
1852 query = line.chomp.strip
1853 break if query.downcase == "quit"
1854 next if query.empty?
1855
1856 begin
1857 response = process_query(query)
1858 puts "\n#{response}"
1859 rescue => e
1860 puts "\nError: #{e.message}"
1861 end
1578}
1579```
1580
1581## Key Components Explained
1582
1583### 1. Client Initialization
1584
1585* The client is initialized using `McpClient.CreateAsync()`, which sets up the transport type and command to run the server.
1586
1587### 2. Server Connection
1588
1589* Supports Python, Node.js, and .NET servers.
1590* The server is started using the command specified in the arguments.
1591* Configures to use stdio for communication with the server.
1592* Initializes the session and available tools.
1593
1594### 3. Query Processing
1595
1596* Leverages [Microsoft.Extensions.AI](https://learn.microsoft.com/dotnet/ai/ai-extensions) for the chat client.
1597* Configures the `IChatClient` to use automatic tool (function) invocation.
1598* The client reads user input and sends it to the server.
1599* The server processes the query and returns a response.
1600* The response is displayed to the user.
1601
1602## Running the Client
1603
1604To run your client with any MCP server:
1605
1606```bash theme={null}
1607dotnet run -- path/to/server.csproj # dotnet server
1608dotnet run -- path/to/server.py # python server
1609dotnet run -- path/to/server.js # node server
1610```
1611
1612> [!NOTE]
1613>
1614> If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `dotnet run -- path/to/QuickstartWeatherServer`.
1615
1616The client will:
1617
16181. Connect to the specified server
16192. List available tools
16203. Start an interactive chat session where you can:
1621 * Enter queries
1622 * See tool executions
1623 * Get responses from Claude
16244. Exit the session when done
1625
1626Here's an example of what it should look like if connected to the weather server quickstart:
1627
1628
1629
1630**Ruby**
1631
1632[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-ruby)
1633
1634## System Requirements
1635
1636Before starting, ensure your system meets these requirements:
1637
1638* Mac or Windows computer
1639* Ruby 3.2.0 or higher installed (required by the [Anthropic SDK](https://github.com/anthropics/anthropic-sdk-ruby))
1640* Anthropic API key (Claude)
1641
1642## Setting Up Your Environment
1643
1644First, create a new Ruby project:
1645
1646```bash macOS/Linux theme={null}
1647# Create project directory
1648mkdir mcp-client
1649cd mcp-client
1650
1651# Create a Gemfile
1652bundle init
1653
1654# Add required dependencies
1655bundle add anthropic base64 dotenv mcp
1656
1657# Create our main file
1658touch client.rb
1659```
1660
1661```powershell Windows theme={null}
1662# Create project directory
1663mkdir mcp-client
1664cd mcp-client
1665
1666# Create a Gemfile
1667bundle init
1668
1669# Add required dependencies
1670bundle add anthropic base64 dotenv mcp
1671
1672# Create our main file
1673new-item client.rb
1674```
1675
1676## Setting Up Your API Key
1677
1678You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1679
1680Create a `.env` file to store it:
1681
1682```bash theme={null}
1683echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
1684```
1685
1686Add `.env` to your `.gitignore`:
1687
1688```bash theme={null}
1689echo ".env" >> .gitignore
1690```
1691
1692> [!WARNING]
1693>
1694> Make sure you keep your `ANTHROPIC_API_KEY` secure!
1695
1696## Creating the Client
1697
1698### Basic Client Structure
1699
1700First, let's set up our requires and create the basic client class:
1701
1702```ruby theme={null}
1703require "anthropic"
1704require "dotenv/load"
1705require "json"
1706require "mcp"
1707
1708class MCPClient
1709 ANTHROPIC_MODEL = "claude-sonnet-4-20250514"
1710
1711 def initialize
1712 @mcp_client = nil
1713 @transport = nil
1714 @anthropic_client = nil
1715 end
1716
1717 # methods will go here
1718end
1719```
1720
1721### Server Connection Management
1722
1723Next, we'll implement the method to connect to an MCP server:
1724
1725```ruby theme={null}
1726def connect_to_server(server_script_path)
1727 command = case File.extname(server_script_path)
1728 when ".rb"
1729 "ruby"
1730 when ".py"
1731 "python3"
1732 when ".js"
1733 "node"
1734 else
1735 raise ArgumentError, "Server script must be a .rb, .py, or .js file."
1736 end
1737
1738 @transport = MCP::Client::Stdio.new(command: command, args: [server_script_path])
1739 @mcp_client = MCP::Client.new(transport: @transport)
1740 @mcp_client.connect
1741
1742 tool_names = @mcp_client.tools.map(&:name)
1743 puts "\nConnected to server with tools: #{tool_names}"
1744end
1745```
1746
1747### Query Processing Logic
1748
1749Now let's add the core functionality for processing queries and handling tool calls:
1750
1751```ruby theme={null}
1752private
1753
1754def process_query(query)
1755 messages = [{ role: "user", content: query }]
1756
1757 available_tools = @mcp_client.tools.map do |tool|
1758 { name: tool.name, description: tool.description, input_schema: tool.input_schema }
1759 end
1760
1761 # Initial Claude API call.
1762 response = chat(messages, tools: available_tools)
1763
1764 # Process response and handle tool calls.
1765 if response.content.any?(Anthropic::Models::ToolUseBlock)
1766 assistant_content = response.content.filter_map do |content_block|
1767 case content_block
1768 when Anthropic::Models::TextBlock
1769 { type: "text", text: content_block.text }
1770 when Anthropic::Models::ToolUseBlock
1771 { type: "tool_use", id: content_block.id, name: content_block.name, input: content_block.input }
18621772 end
18631773 end
1864
1865 def cleanup
1866 @transport&.close
1774 messages << { role: "assistant", content: assistant_content }
1775 end
1776
1777 response.content.each_with_object([]) do |content, response_parts|
1778 case content
1779 when Anthropic::Models::TextBlock
1780 response_parts << content.text
1781 when Anthropic::Models::ToolUseBlock
1782 # Execute tool call via MCP.
1783 result = @mcp_client.call_tool(name: content.name, arguments: content.input)
1784 response_parts << "[Calling tool #{content.name} with args #{content.input.to_json}]"
1785
1786 tool_result_content = result.dig("result", "content")
1787 result_text = if tool_result_content.is_a?(Array)
1788 tool_result_content.filter_map { |content_item| content_item["text"] }.join("\n")
1789 else
1790 tool_result_content.to_s
1791 end
1792
1793 messages << {
1794 role: "user",
1795 content: [{
1796 type: "tool_result",
1797 tool_use_id: content.id,
1798 content: result_text
1799 }]
1800 }
1801
1802 # Get next response from Claude.
1803 response = chat(messages)
1804
1805 response.content.each do |content_block|
1806 response_parts << content_block.text if content_block.is_a?(Anthropic::Models::TextBlock)
1807 end
18671808 end
1868 ```
1869
1870 ### Main Entry Point
1871
1872 Finally, we'll add the main execution logic:
1873
1874 ```ruby theme={null}
1875 if ARGV.empty?
1876 puts "Usage: ruby client.rb <path_to_server_script>"
1877 exit 1
1809 end.join("\n")
1810end
1811
1812def chat(messages, tools: nil)
1813 params = { model: ANTHROPIC_MODEL, max_tokens: 1000, messages: messages }
1814 params[:tools] = tools if tools
1815
1816 anthropic_client.messages.create(**params)
1817end
1818
1819def anthropic_client
1820 @anthropic_client ||= Anthropic::Client.new(api_key: ENV["ANTHROPIC_API_KEY"])
1821end
1822```
1823
1824### Interactive Chat Interface
1825
1826Now we'll add the chat loop and cleanup functionality:
1827
1828```ruby theme={null}
1829def chat_loop
1830 puts <<~MESSAGE
1831 MCP Client Started!
1832 Type your queries or 'quit' to exit.
1833 MESSAGE
1834
1835 loop do
1836 print "\nQuery: "
1837 line = $stdin.gets
1838 break if line.nil?
1839
1840 query = line.chomp.strip
1841 break if query.downcase == "quit"
1842 next if query.empty?
1843
1844 begin
1845 response = process_query(query)
1846 puts "\n#{response}"
1847 rescue => e
1848 puts "\nError: #{e.message}"
18781849 end
1879
1880 client = MCPClient.new
1881
1882 begin
1883 client.connect_to_server(ARGV[0])
1884
1885 api_key = ENV["ANTHROPIC_API_KEY"]
1886 if api_key.nil? || api_key.empty?
1887 puts <<~MESSAGE
1888 No ANTHROPIC_API_KEY found. To query these tools with Claude, set your API key:
1889 export ANTHROPIC_API_KEY=your-api-key-here
1890 MESSAGE
1891 exit
1892 end
1893
1894 client.chat_loop
1895 rescue => e
1896 puts "Error: #{e.message}"
1897 exit 1
1898 ensure
1899 client.cleanup
1900 end
1901 ```
1902
1903 You can find the complete `client.rb` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-ruby/client.rb).
1904
1905 ## Key Components Explained
1906
1907 ### 1. Client Initialization
1908
1909 * The `MCPClient` class initializes with nil references for lazy setup
1910 * The Anthropic client is lazily initialized via the `anthropic_client` method
1911 * Uses `dotenv` to load environment variables from `.env`
1912
1913 ### 2. Server Connection
1914
1915 * Supports Ruby, Python, and Node.js servers
1916 * Uses `File.extname` to determine the server script type
1917 * Uses `MCP::Client::Stdio` for stdio transport
1918 * Initializes the MCP client and lists available tools
1919
1920 ### 3. Query Processing
1921
1922 * Maps MCP tools to Anthropic tool format (`name`, `description`, `input_schema`)
1923 * Uses `Anthropic::Models::TextBlock` and `Anthropic::Models::ToolUseBlock` for pattern matching
1924 * Builds assistant content once before iterating tool calls
1925 * Executes tool calls via `@mcp_client.call_tool`
1926 * Uses `chat` helper method to wrap Anthropic API calls
1927 * Extracts tool result content with `result.dig("result", "content")`
1928 * Passes tool results back to Claude for a final response
1929
1930 ### 4. Interactive Interface
1931
1932 * Provides a simple command-line interface
1933 * Handles user input and displays responses
1934 * Skips empty queries
1935 * Includes basic error handling
1936
1937 ### 5. Resource Management
1938
1939 * Proper cleanup of the transport via `begin`...`ensure`
1940 * Top-level `rescue` for error handling
1941 * API key validation after server connection
1942
1943 ## Running the Client
1944
1945 To run your client with any MCP server:
1946
1947 ```bash theme={null}
1948 bundle exec ruby client.rb path/to/server.rb # ruby server
1949 bundle exec ruby client.rb path/to/server.py # python server
1950 bundle exec ruby client.rb path/to/build/index.js # node server
1951 ```
1952
1953 <Note>
1954 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby), your command might look something like this: `bundle exec ruby client.rb /path/to/weather-server-ruby/weather.rb`
1955 </Note>
1956
1957 The client will:
1958
1959 1. Connect to the specified server
1960 2. List available tools
1961 3. Start an interactive chat session where you can:
1962 * Enter queries
1963 * See tool executions
1964 * Get responses from Claude
1965
1966 ## How It Works
1967
1968 When you submit a query:
1969
1970 1. The client gets the list of available tools from the server
1971 2. Your query is sent to Claude along with tool descriptions
1972 3. Claude decides which tools (if any) to use
1973 4. The client executes any requested tool calls through the server
1974 5. Results are sent back to Claude
1975 6. Claude provides a natural language response
1976 7. The response is displayed to you
1977
1978 ## Best practices
1979
1980 1. **Error Handling**
1981 * Wrap tool calls in `begin`...`rescue` blocks
1982 * Provide meaningful error messages
1983 * Gracefully handle connection issues
1984
1985 2. **Resource Management**
1986 * Always close the transport when done
1987 * Use `begin`...`ensure` for proper cleanup
1988 * Handle server disconnections
1989
1990 3. **Security**
1991 * Store API keys securely in `.env`
1992 * Validate server responses
1993 * Be cautious with tool permissions
1994
1995 4. **Tool Names**
1996 * Tool names can be validated according to the format specified [here](/specification/2025-11-25/server/tools#tool-names)
1997 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
1998
1999 ## Troubleshooting
2000
2001 ### Server Path Issues
2002
2003 * Double-check the path to your server script is correct
2004 * Use the absolute path if the relative path isn't working
2005 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
2006 * Verify the server file has the correct extension (.py for Python, .js for Node.js, or .rb for Ruby)
2007
2008 Example of correct path usage:
2009
2010 ```bash theme={null}
2011 # Relative path
2012 bundle exec ruby client.rb ./server/weather.rb
2013
2014 # Absolute path
2015 bundle exec ruby client.rb /Users/username/projects/mcp-server/weather.rb
2016
2017 # Windows path (either format works)
2018 bundle exec ruby client.rb C:/projects/mcp-server/weather.rb
2019 bundle exec ruby client.rb C:\\projects\\mcp-server\\weather.rb
2020 ```
2021
2022 ### Response Timing
2023
2024 * The first response might take up to 30 seconds to return
2025 * This is normal and happens while:
2026 * The server initializes
2027 * Claude processes the query
2028 * Tools are being executed
2029 * Subsequent responses are typically faster
2030 * Don't interrupt the process during this initial waiting period
2031
2032 ### Common Error Messages
2033
2034 If you see:
2035
2036 * `Errno::ENOENT`: Check your server path and ensure the command (`ruby`, `python3`, `node`) is available
2037 * `Connection refused`: Ensure the server is running and the path is correct
2038 * `Tool execution failed`: Verify the tool's required environment variables are set
2039 * `Anthropic::Errors::AuthenticationError`: Check your `.env` file has a valid `ANTHROPIC_API_KEY`
2040 </Tab>
2041
2042 <Tab title="Rust">
2043 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-rust)
2044
2045 ## System Requirements
2046
2047 Before starting, ensure your Linux system meets these requirements:
2048
2049 * Latest stable version of [Rust and Cargo](https://www.rust-lang.org/tools/install)
2050 * Anthropic API key (Claude)
2051 * A Python, Node.js, or executable MCP server to connect to
2052
2053 ## Setting Up Your Environment
2054
2055 First, create a new Rust project:
2056
2057 ```bash theme={null}
2058 cargo new mcp-client-rust
2059 cd mcp-client-rust
2060 ```
2061
2062 Replace the contents of `Cargo.toml` with the following:
2063
2064 ```toml Cargo.toml theme={null}
2065 [package]
2066 name = "mcp-client-rust"
2067 version = "0.1.0"
2068 edition = "2024"
2069
2070 [dependencies]
2071 anyhow = "1.0.100"
2072 genai = "0.4.2"
2073 rmcp = { version = "0.8.0", features = ["server", "client", "transport-io", "transport-child-process"] }
2074 tokio = { version = "1.47.1", features = ["full"] }
2075 tracing = "0.1.41"
2076 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
2077 serde_json = "1.0.128"
2078 dotenvy = "0.15.7"
2079 reqwest = "0.12.23"
2080 ```
2081
2082 The [`rmcp`](https://github.com/modelcontextprotocol/rust-sdk) crate provides the Rust MCP SDK and child-process transport. This example uses the [`genai`](https://github.com/jeremychone/rust-genai) crate to send requests to Claude and represent tools in the model request.
2083
2084 ## Setting Up Your API Key
2085
2086 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
2087
2088 Create a `.env` file to store it:
2089
2090 ```bash theme={null}
2091 echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
2092 ```
2093
2094 Add `.env` to your `.gitignore`:
2095
2096 ```bash theme={null}
2097 echo ".env" >> .gitignore
2098 ```
2099
2100 <Warning>
2101 Make sure you keep your `ANTHROPIC_API_KEY` secure!
2102 </Warning>
2103
2104 ## Creating the Client
2105
2106 Open `src/main.rs` and replace its contents as you work through the following sections.
2107
2108 ### Imports and Client Structure
2109
2110 First, add the imports, model constant, and basic client structure:
2111
2112 ```rust theme={null}
2113 use anyhow::{Context, Result, bail};
2114 use genai::Client;
2115 use genai::chat::{
2116 ChatMessage, ChatRequest, ChatResponse, ContentPart, Tool as GenaiTool, ToolResponse,
2117 };
2118 use rmcp::model::{CallToolRequestParam, Tool as McpTool};
2119 use rmcp::service::{RoleClient, RunningService, ServiceExt};
2120 use rmcp::transport::TokioChildProcess;
2121 use serde_json::Value;
2122 use tokio::io::{self, AsyncBufReadExt, BufReader};
2123 use tokio::process::Command;
2124
2125 const MODEL_ANTHROPIC: &str = "claude-sonnet-4-20250514";
2126
2127 struct MCPClient {
2128 anthropic: Client,
2129 session: Option<RunningService<RoleClient, ()>>,
2130 tools: Vec<GenaiTool>,
1850 end
1851end
1852
1853def cleanup
1854 @transport&.close
1855end
1856```
1857
1858### Main Entry Point
1859
1860Finally, we'll add the main execution logic:
1861
1862```ruby theme={null}
1863if ARGV.empty?
1864 puts "Usage: ruby client.rb <path_to_server_script>"
1865 exit 1
1866end
1867
1868client = MCPClient.new
1869
1870begin
1871 client.connect_to_server(ARGV[0])
1872
1873 api_key = ENV["ANTHROPIC_API_KEY"]
1874 if api_key.nil? || api_key.empty?
1875 puts <<~MESSAGE
1876 No ANTHROPIC_API_KEY found. To query these tools with Claude, set your API key:
1877 export ANTHROPIC_API_KEY=your-api-key-here
1878 MESSAGE
1879 exit
1880 end
1881
1882 client.chat_loop
1883rescue => e
1884 puts "Error: #{e.message}"
1885 exit 1
1886ensure
1887 client.cleanup
1888end
1889```
1890
1891You can find the complete `client.rb` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-ruby/client.rb).
1892
1893## Key Components Explained
1894
1895### 1. Client Initialization
1896
1897* The `MCPClient` class initializes with nil references for lazy setup
1898* The Anthropic client is lazily initialized via the `anthropic_client` method
1899* Uses `dotenv` to load environment variables from `.env`
1900
1901### 2. Server Connection
1902
1903* Supports Ruby, Python, and Node.js servers
1904* Uses `File.extname` to determine the server script type
1905* Uses `MCP::Client::Stdio` for stdio transport
1906* Initializes the MCP client and lists available tools
1907
1908### 3. Query Processing
1909
1910* Maps MCP tools to Anthropic tool format (`name`, `description`, `input_schema`)
1911* Uses `Anthropic::Models::TextBlock` and `Anthropic::Models::ToolUseBlock` for pattern matching
1912* Builds assistant content once before iterating tool calls
1913* Executes tool calls via `@mcp_client.call_tool`
1914* Uses `chat` helper method to wrap Anthropic API calls
1915* Extracts tool result content with `result.dig("result", "content")`
1916* Passes tool results back to Claude for a final response
1917
1918### 4. Interactive Interface
1919
1920* Provides a simple command-line interface
1921* Handles user input and displays responses
1922* Skips empty queries
1923* Includes basic error handling
1924
1925### 5. Resource Management
1926
1927* Proper cleanup of the transport via `begin`...`ensure`
1928* Top-level `rescue` for error handling
1929* API key validation after server connection
1930
1931## Running the Client
1932
1933To run your client with any MCP server:
1934
1935```bash theme={null}
1936bundle exec ruby client.rb path/to/server.rb # ruby server
1937bundle exec ruby client.rb path/to/server.py # python server
1938bundle exec ruby client.rb path/to/build/index.js # node server
1939```
1940
1941> [!NOTE]
1942>
1943> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby), your command might look something like this: `bundle exec ruby client.rb /path/to/weather-server-ruby/weather.rb`
1944
1945The client will:
1946
19471. Connect to the specified server
19482. List available tools
19493. Start an interactive chat session where you can:
1950 * Enter queries
1951 * See tool executions
1952 * Get responses from Claude
1953
1954## How It Works
1955
1956When you submit a query:
1957
19581. The client gets the list of available tools from the server
19592. Your query is sent to Claude along with tool descriptions
19603. Claude decides which tools (if any) to use
19614. The client executes any requested tool calls through the server
19625. Results are sent back to Claude
19636. Claude provides a natural language response
19647. The response is displayed to you
1965
1966## Best practices
1967
19681. **Error Handling**
1969 * Wrap tool calls in `begin`...`rescue` blocks
1970 * Provide meaningful error messages
1971 * Gracefully handle connection issues
1972
19732. **Resource Management**
1974 * Always close the transport when done
1975 * Use `begin`...`ensure` for proper cleanup
1976 * Handle server disconnections
1977
19783. **Security**
1979 * Store API keys securely in `.env`
1980 * Validate server responses
1981 * Be cautious with tool permissions
1982
19834. **Tool Names**
1984 * Tool names can be validated according to the format specified [here](/specification/2025-11-25/server/tools#tool-names)
1985 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
1986
1987## Troubleshooting
1988
1989### Server Path Issues
1990
1991* Double-check the path to your server script is correct
1992* Use the absolute path if the relative path isn't working
1993* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
1994* Verify the server file has the correct extension (.py for Python, .js for Node.js, or .rb for Ruby)
1995
1996Example of correct path usage:
1997
1998```bash theme={null}
1999# Relative path
2000bundle exec ruby client.rb ./server/weather.rb
2001
2002# Absolute path
2003bundle exec ruby client.rb /Users/username/projects/mcp-server/weather.rb
2004
2005# Windows path (either format works)
2006bundle exec ruby client.rb C:/projects/mcp-server/weather.rb
2007bundle exec ruby client.rb C:\\projects\\mcp-server\\weather.rb
2008```
2009
2010### Response Timing
2011
2012* The first response might take up to 30 seconds to return
2013* This is normal and happens while:
2014 * The server initializes
2015 * Claude processes the query
2016 * Tools are being executed
2017* Subsequent responses are typically faster
2018* Don't interrupt the process during this initial waiting period
2019
2020### Common Error Messages
2021
2022If you see:
2023
2024* `Errno::ENOENT`: Check your server path and ensure the command (`ruby`, `python3`, `node`) is available
2025* `Connection refused`: Ensure the server is running and the path is correct
2026* `Tool execution failed`: Verify the tool's required environment variables are set
2027* `Anthropic::Errors::AuthenticationError`: Check your `.env` file has a valid `ANTHROPIC_API_KEY`
2028
2029**Rust**
2030
2031[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-rust)
2032
2033## System Requirements
2034
2035Before starting, ensure your Linux system meets these requirements:
2036
2037* Latest stable version of [Rust and Cargo](https://www.rust-lang.org/tools/install)
2038* Anthropic API key (Claude)
2039* A Python, Node.js, or executable MCP server to connect to
2040
2041## Setting Up Your Environment
2042
2043First, create a new Rust project:
2044
2045```bash theme={null}
2046cargo new mcp-client-rust
2047cd mcp-client-rust
2048```
2049
2050Replace the contents of `Cargo.toml` with the following:
2051
2052```toml Cargo.toml theme={null}
2053[package]
2054name = "mcp-client-rust"
2055version = "0.1.0"
2056edition = "2024"
2057
2058[dependencies]
2059anyhow = "1.0.100"
2060genai = "0.4.2"
2061rmcp = { version = "0.8.0", features = ["server", "client", "transport-io", "transport-child-process"] }
2062tokio = { version = "1.47.1", features = ["full"] }
2063tracing = "0.1.41"
2064tracing-subscriber = { version = "0.3", features = ["env-filter"] }
2065serde_json = "1.0.128"
2066dotenvy = "0.15.7"
2067reqwest = "0.12.23"
2068```
2069
2070The [`rmcp`](https://github.com/modelcontextprotocol/rust-sdk) crate provides the Rust MCP SDK and child-process transport. This example uses the [`genai`](https://github.com/jeremychone/rust-genai) crate to send requests to Claude and represent tools in the model request.
2071
2072## Setting Up Your API Key
2073
2074You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
2075
2076Create a `.env` file to store it:
2077
2078```bash theme={null}
2079echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
2080```
2081
2082Add `.env` to your `.gitignore`:
2083
2084```bash theme={null}
2085echo ".env" >> .gitignore
2086```
2087
2088> [!WARNING]
2089>
2090> Make sure you keep your `ANTHROPIC_API_KEY` secure!
2091
2092## Creating the Client
2093
2094Open `src/main.rs` and replace its contents as you work through the following sections.
2095
2096### Imports and Client Structure
2097
2098First, add the imports, model constant, and basic client structure:
2099
2100```rust theme={null}
2101use anyhow::{Context, Result, bail};
2102use genai::Client;
2103use genai::chat::{
2104 ChatMessage, ChatRequest, ChatResponse, ContentPart, Tool as GenaiTool, ToolResponse,
2105};
2106use rmcp::model::{CallToolRequestParam, Tool as McpTool};
2107use rmcp::service::{RoleClient, RunningService, ServiceExt};
2108use rmcp::transport::TokioChildProcess;
2109use serde_json::Value;
2110use tokio::io::{self, AsyncBufReadExt, BufReader};
2111use tokio::process::Command;
2112
2113const MODEL_ANTHROPIC: &str = "claude-sonnet-4-20250514";
2114
2115struct MCPClient {
2116 anthropic: Client,
2117 session: Option<RunningService<RoleClient, ()>>,
2118 tools: Vec<GenaiTool>,
2119}
2120```
2121
2122The client keeps the model API client, the active MCP session, and the tools advertised by the connected server.
2123
2124### Client Initialization
2125
2126Next, initialize the model client and start without an MCP session or tools:
2127
2128```rust theme={null}
2129impl MCPClient {
2130 fn new() -> Result<Self> {
2131 Ok(MCPClient {
2132 anthropic: Client::default(),
2133 session: None,
2134 tools: Vec::new(),
2135 })
21312136 }
2132 ```
2133
2134 The client keeps the model API client, the active MCP session, and the tools advertised by the connected server.
2135
2136 ### Client Initialization
2137
2138 Next, initialize the model client and start without an MCP session or tools:
2139
2140 ```rust theme={null}
2141 impl MCPClient {
2142 fn new() -> Result<Self> {
2143 Ok(MCPClient {
2144 anthropic: Client::default(),
2145 session: None,
2146 tools: Vec::new(),
2147 })
2137
2138 // Additional methods will go here.
2139}
2140```
2141
2142`genai::Client::default()` reads the `ANTHROPIC_API_KEY` environment variable when it sends a request.
2143
2144### Server Connection Management
2145
2146Add this method inside the `impl MCPClient` block:
2147
2148```rust theme={null}
2149async fn connect_to_server(&mut self, server_args: &[String]) -> Result<()> {
2150 if self.session.is_some() {
2151 bail!("Client is already connected to a server");
2152 }
2153
2154 let mut command = Command::new(&server_args[0]);
2155 command.args(&server_args[1..]);
2156
2157 let process = TokioChildProcess::new(command)
2158 .with_context(|| format!("Failed to spawn server process for {:?}", server_args))?;
2159
2160 let session = ().serve(process).await?;
2161
2162 let rmcp_tools = session
2163 .list_all_tools()
2164 .await
2165 .context("Unable to list tools from server")?;
2166
2167 let tool_names: Vec<String> = rmcp_tools
2168 .iter()
2169 .map(|tool| tool.name.to_string())
2170 .collect();
2171
2172 println!("Connected to server with tools: {tool_names:?}");
2173
2174 self.tools = convert_tools(&rmcp_tools);
2175 self.session = Some(session);
2176 Ok(())
2177}
2178```
2179
2180This method:
2181
21821. Starts the server as a child process using the command and arguments supplied on the command line
21832. Establishes an MCP session over stdio
21843. Lists all tools advertised by the server
21854. Converts those tools into the format used in model requests
2186
2187### Converting MCP Tools
2188
2189Add this function outside the `impl MCPClient` block:
2190
2191```rust theme={null}
2192fn convert_tools(tools: &[McpTool]) -> Vec<GenaiTool> {
2193 tools
2194 .iter()
2195 .map(|tool| GenaiTool {
2196 name: tool.name.to_string(),
2197 description: tool.description.as_deref().map(str::to_string),
2198 schema: Some(Value::Object(tool.input_schema.as_ref().clone())),
2199 config: None,
2200 })
2201 .collect()
2202}
2203```
2204
2205MCP and model APIs describe tools with similar information but different Rust types. `convert_tools` maps each MCP tool's name, description, and input schema into a `genai` tool definition.
2206
2207### Sending Model Requests
2208
2209Add this helper method inside `impl MCPClient`:
2210
2211```rust theme={null}
2212async fn request_model(&self, chat_req: &ChatRequest) -> Result<ChatResponse> {
2213 let response = self
2214 .anthropic
2215 .exec_chat(MODEL_ANTHROPIC, chat_req.clone(), None)
2216 .await
2217 .context("Anthropic chat request failed")?;
2218
2219 Ok(response)
2220}
2221```
2222
2223This keeps model request handling in one place and adds useful context if the API request fails.
2224
2225### Query Processing Logic
2226
2227Now add the core query-processing method inside `impl MCPClient`:
2228
2229```rust theme={null}
2230async fn process_query(&mut self, query: &str) -> Result<String> {
2231 let session = self
2232 .session
2233 .as_ref()
2234 .context("Client is not connected to any server")?;
2235
2236 let mut messages = vec![ChatMessage::user(query)];
2237 let mut final_text = Vec::new();
2238
2239 // Initial Claude API call with tools
2240 let mut chat_req = ChatRequest::new(messages.clone()).with_tools(self.tools.clone());
2241 let mut chat_rsp = self.request_model(&chat_req).await?;
2242
2243 // Process response content - collect text and handle tool calls
2244 for text in chat_rsp.texts() {
2245 final_text.push(text.to_string());
2246 }
2247
2248 let tool_calls = chat_rsp.tool_calls();
2249 if !tool_calls.is_empty() {
2250 // Append assistant's response to message history
2251 messages.push(ChatMessage::assistant(chat_rsp.content.clone()));
2252
2253 // Execute each tool call and collect responses
2254 let mut tool_results = Vec::new();
2255 for tool_call in tool_calls {
2256 // Add information about the tool call to final text
2257 let tool_args_str = serde_json::to_string(&tool_call.fn_arguments)
2258 .unwrap_or_else(|_| "{}".to_string());
2259
2260 final_text.push(format!(
2261 "[Calling tool {} with args {}]",
2262 tool_call.fn_name, tool_args_str
2263 ));
2264
2265 // Query the MCP server
2266 let tool_result = session
2267 .call_tool(CallToolRequestParam {
2268 name: tool_call.fn_name.clone().into(),
2269 arguments: tool_call.fn_arguments.as_object().cloned(),
2270 })
2271 .await
2272 .with_context(|| format!("Tool call {} failed", tool_call.fn_name))?;
2273
2274 let payload = serde_json::to_string(&tool_result)
2275 .context("Failed to serialize tool result")?;
2276
2277 tool_results.push(ContentPart::ToolResponse(ToolResponse::new(
2278 tool_call.call_id.clone(),
2279 payload,
2280 )));
21482281 }
21492282
2150 // Additional methods will go here.
2151 }
2152 ```
2153
2154 `genai::Client::default()` reads the `ANTHROPIC_API_KEY` environment variable when it sends a request.
2155
2156 ### Server Connection Management
2157
2158 Add this method inside the `impl MCPClient` block:
2159
2160 ```rust theme={null}
2161 async fn connect_to_server(&mut self, server_args: &[String]) -> Result<()> {
2162 if self.session.is_some() {
2163 bail!("Client is already connected to a server");
2164 }
2165
2166 let mut command = Command::new(&server_args[0]);
2167 command.args(&server_args[1..]);
2168
2169 let process = TokioChildProcess::new(command)
2170 .with_context(|| format!("Failed to spawn server process for {:?}", server_args))?;
2171
2172 let session = ().serve(process).await?;
2173
2174 let rmcp_tools = session
2175 .list_all_tools()
2176 .await
2177 .context("Unable to list tools from server")?;
2178
2179 let tool_names: Vec<String> = rmcp_tools
2180 .iter()
2181 .map(|tool| tool.name.to_string())
2182 .collect();
2183
2184 println!("Connected to server with tools: {tool_names:?}");
2185
2186 self.tools = convert_tools(&rmcp_tools);
2187 self.session = Some(session);
2188 Ok(())
2189 }
2190 ```
2191
2192 This method:
2193
2194 1. Starts the server as a child process using the command and arguments supplied on the command line
2195 2. Establishes an MCP session over stdio
2196 3. Lists all tools advertised by the server
2197 4. Converts those tools into the format used in model requests
2198
2199 ### Converting MCP Tools
2200
2201 Add this function outside the `impl MCPClient` block:
2202
2203 ```rust theme={null}
2204 fn convert_tools(tools: &[McpTool]) -> Vec<GenaiTool> {
2205 tools
2206 .iter()
2207 .map(|tool| GenaiTool {
2208 name: tool.name.to_string(),
2209 description: tool.description.as_deref().map(str::to_string),
2210 schema: Some(Value::Object(tool.input_schema.as_ref().clone())),
2211 config: None,
2212 })
2213 .collect()
2214 }
2215 ```
2216
2217 MCP and model APIs describe tools with similar information but different Rust types. `convert_tools` maps each MCP tool's name, description, and input schema into a `genai` tool definition.
2218
2219 ### Sending Model Requests
2220
2221 Add this helper method inside `impl MCPClient`:
2222
2223 ```rust theme={null}
2224 async fn request_model(&self, chat_req: &ChatRequest) -> Result<ChatResponse> {
2225 let response = self
2226 .anthropic
2227 .exec_chat(MODEL_ANTHROPIC, chat_req.clone(), None)
2228 .await
2229 .context("Anthropic chat request failed")?;
2230
2231 Ok(response)
2232 }
2233 ```
2234
2235 This keeps model request handling in one place and adds useful context if the API request fails.
2236
2237 ### Query Processing Logic
2238
2239 Now add the core query-processing method inside `impl MCPClient`:
2240
2241 ```rust theme={null}
2242 async fn process_query(&mut self, query: &str) -> Result<String> {
2243 let session = self
2244 .session
2245 .as_ref()
2246 .context("Client is not connected to any server")?;
2247
2248 let mut messages = vec![ChatMessage::user(query)];
2249 let mut final_text = Vec::new();
2250
2251 // Initial Claude API call with tools
2252 let mut chat_req = ChatRequest::new(messages.clone()).with_tools(self.tools.clone());
2253 let mut chat_rsp = self.request_model(&chat_req).await?;
2254
2255 // Process response content - collect text and handle tool calls
2283 // Append tool responses to message history
2284 messages.push(ChatMessage::user(tool_results));
2285
2286 // Build the next request and query model
2287 chat_req = ChatRequest::new(messages.clone());
2288 chat_rsp = self.request_model(&chat_req).await?;
2289
2290 // Collect text from response
22562291 for text in chat_rsp.texts() {
22572292 final_text.push(text.to_string());
22582293 }
2259
2260 let tool_calls = chat_rsp.tool_calls();
2261 if !tool_calls.is_empty() {
2262 // Append assistant's response to message history
2263 messages.push(ChatMessage::assistant(chat_rsp.content.clone()));
2264
2265 // Execute each tool call and collect responses
2266 let mut tool_results = Vec::new();
2267 for tool_call in tool_calls {
2268 // Add information about the tool call to final text
2269 let tool_args_str = serde_json::to_string(&tool_call.fn_arguments)
2270 .unwrap_or_else(|_| "{}".to_string());
2271
2272 final_text.push(format!(
2273 "[Calling tool {} with args {}]",
2274 tool_call.fn_name, tool_args_str
2275 ));
2276
2277 // Query the MCP server
2278 let tool_result = session
2279 .call_tool(CallToolRequestParam {
2280 name: tool_call.fn_name.clone().into(),
2281 arguments: tool_call.fn_arguments.as_object().cloned(),
2282 })
2283 .await
2284 .with_context(|| format!("Tool call {} failed", tool_call.fn_name))?;
2285
2286 let payload = serde_json::to_string(&tool_result)
2287 .context("Failed to serialize tool result")?;
2288
2289 tool_results.push(ContentPart::ToolResponse(ToolResponse::new(
2290 tool_call.call_id.clone(),
2291 payload,
2292 )));
2293 }
2294
2295 // Append tool responses to message history
2296 messages.push(ChatMessage::user(tool_results));
2297
2298 // Build the next request and query model
2299 chat_req = ChatRequest::new(messages.clone());
2300 chat_rsp = self.request_model(&chat_req).await?;
2301
2302 // Collect text from response
2303 for text in chat_rsp.texts() {
2304 final_text.push(text.to_string());
2305 }
2294 }
2295
2296 Ok(final_text.join("\n"))
2297}
2298```
2299
2300The method first sends the user's query and available tools to Claude. When Claude requests tools, the client executes each request through the MCP session, sends the results back to Claude, and collects the final text response.
2301
2302### Interactive Chat Interface
2303
2304Add the interactive terminal loop inside `impl MCPClient`:
2305
2306```rust theme={null}
2307async fn chat_loop(&mut self) -> Result<()> {
2308 println!("\nMCP Client Started!");
2309 println!("Type your queries or 'quit' to exit.");
2310
2311 let mut stdin = BufReader::new(io::stdin());
2312 let mut input = String::new();
2313
2314 loop {
2315 print!("\nQuery: ");
2316 std::io::Write::flush(&mut std::io::stdout())?;
2317
2318 input.clear();
2319 if stdin.read_line(&mut input).await? == 0 {
2320 break; // EOF
23062321 }
23072322
2308 Ok(final_text.join("\n"))
2323 let query = input.trim();
2324 if query.eq_ignore_ascii_case("quit") {
2325 break;
2326 }
2327 if query.is_empty() {
2328 continue;
2329 }
2330
2331 match self.process_query(query).await {
2332 Ok(response) => println!("\n{}", response),
2333 Err(err) => println!("\nError: {}", err),
2334 }
23092335 }
2310 ```
2311
2312 The method first sends the user's query and available tools to Claude. When Claude requests tools, the client executes each request through the MCP session, sends the results back to Claude, and collects the final text response.
2313
2314 ### Interactive Chat Interface
2315
2316 Add the interactive terminal loop inside `impl MCPClient`:
2317
2318 ```rust theme={null}
2319 async fn chat_loop(&mut self) -> Result<()> {
2320 println!("\nMCP Client Started!");
2321 println!("Type your queries or 'quit' to exit.");
2322
2323 let mut stdin = BufReader::new(io::stdin());
2324 let mut input = String::new();
2325
2326 loop {
2327 print!("\nQuery: ");
2328 std::io::Write::flush(&mut std::io::stdout())?;
2329
2330 input.clear();
2331 if stdin.read_line(&mut input).await? == 0 {
2332 break; // EOF
2333 }
2334
2335 let query = input.trim();
2336 if query.eq_ignore_ascii_case("quit") {
2337 break;
2338 }
2339 if query.is_empty() {
2340 continue;
2341 }
2342
2343 match self.process_query(query).await {
2344 Ok(response) => println!("\n{}", response),
2345 Err(err) => println!("\nError: {}", err),
2346 }
2347 }
2348
2349 Ok(())
2336
2337 Ok(())
2338}
2339```
2340
2341The loop accepts queries until the user types `quit` or closes standard input. Query errors are printed without terminating the client.
2342
2343### Cleanup
2344
2345Add this method inside `impl MCPClient` to stop the MCP session and child process:
2346
2347```rust theme={null}
2348async fn cleanup(&mut self) -> Result<()> {
2349 if let Some(session) = self.session.take() {
2350 let _ = session.cancel().await;
23502351 }
2351 ```
2352
2353 The loop accepts queries until the user types `quit` or closes standard input. Query errors are printed without terminating the client.
2354
2355 ### Cleanup
2356
2357 Add this method inside `impl MCPClient` to stop the MCP session and child process:
2358
2359 ```rust theme={null}
2360 async fn cleanup(&mut self) -> Result<()> {
2361 if let Some(session) = self.session.take() {
2362 let _ = session.cancel().await;
2363 }
2364 Ok(())
2352 Ok(())
2353}
2354```
2355
2356### Main Entry Point
2357
2358Finally, add the asynchronous entry point outside the `impl MCPClient` block:
2359
2360```rust theme={null}
2361#[tokio::main]
2362async fn main() -> Result<()> {
2363 dotenvy::dotenv().context("Failed to load env file")?;
2364
2365 let mut args = std::env::args();
2366 let _ = args.next();
2367 let server_args: Vec<String> = args.collect();
2368
2369 if server_args.is_empty() {
2370 eprintln!("Usage: cargo run -- <server_script_or_binary> [args...]");
2371 std::process::exit(1);
23652372 }
2366 ```
2367
2368 ### Main Entry Point
2369
2370 Finally, add the asynchronous entry point outside the `impl MCPClient` block:
2371
2372 ```rust theme={null}
2373 #[tokio::main]
2374 async fn main() -> Result<()> {
2375 dotenvy::dotenv().context("Failed to load env file")?;
2376
2377 let mut args = std::env::args();
2378 let _ = args.next();
2379 let server_args: Vec<String> = args.collect();
2380
2381 if server_args.is_empty() {
2382 eprintln!("Usage: cargo run -- <server_script_or_binary> [args...]");
2383 std::process::exit(1);
2384 }
2385
2386 let mut client = MCPClient::new()?;
2387
2388 let result = async {
2389 client.connect_to_server(&server_args).await?;
2390 client.chat_loop().await
2391 }
2392 .await;
2393
2394 let cleanup_result = client.cleanup().await;
2395
2396 result?;
2397 cleanup_result?;
2398
2399 Ok(())
2373
2374 let mut client = MCPClient::new()?;
2375
2376 let result = async {
2377 client.connect_to_server(&server_args).await?;
2378 client.chat_loop().await
24002379 }
2401 ```
2402
2403 The entry point loads `.env`, treats all remaining command-line arguments as the server command, connects the client, starts the chat loop, and ensures cleanup runs before exiting.
2404
2405 ### Verify the Complete File
2406
2407 Before running the client, confirm the items in `src/main.rs` are placed at the correct scope:
2408
2409 * `new`, `connect_to_server`, `process_query`, `request_model`, `chat_loop`, and `cleanup` are methods inside the single `impl MCPClient` block.
2410 * `main` and `convert_tools` are functions outside the `impl MCPClient` block.
2411
2412 Rust does not require these items to appear in a particular order, but methods and free functions must be placed in the correct scope. Compare your file with the [complete `src/main.rs` example](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-rust/src/main.rs), then check that it compiles:
2413
2414 ```bash theme={null}
2415 cargo fmt --check
2416 cargo check
2417 ```
2418
2419 ## Running the Client
2420
2421 Use `cargo run --` followed by the command you would normally use to start the MCP server:
2422
2423 ```bash theme={null}
2424 # Python server
2425 cargo run -- python path/to/server.py
2426
2427 # Node.js server
2428 cargo run -- node path/to/build/index.js
2429
2430 # Executable server
2431 cargo run -- path/to/server-binary
2432 ```
2433
2434 Running bare `cargo run` without a server command prints the usage message and exits.
2435
2436 <Note>
2437 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust), build the server first and then run a command similar to: `cargo run -- ../weather-server-rust/target/debug/weather`
2438 </Note>
2439
2440 The client will:
2441
2442 1. Start and connect to the specified MCP server
2443 2. List the tools available from that server
2444 3. Start an interactive chat session where you can:
2445 * Enter queries
2446 * See tool executions
2447 * Get responses from Claude
2448
2449 ## How It Works
2450
2451 When you submit a query:
2452
2453 1. The client sends your query and the server's available tools to Claude
2454 2. Claude decides which tools, if any, to use
2455 3. The client executes requested tools through the MCP session
2456 4. Tool results are sent back to Claude
2457 5. Claude provides a natural language response
2458 6. The response is displayed in the terminal
2459
2460 ## Best Practices
2461
2462 1. **Error Handling**
2463 * Add context to errors at process, MCP, model API, and serialization boundaries
2464 * Report individual query errors without terminating the interactive session
2465 * Validate server commands before running them
2466
2467 2. **Resource Management**
2468 * Always cancel the MCP session during cleanup
2469 * Ensure cleanup runs even when connection or chat-loop operations fail
2470 * Avoid starting a second server while a session is active
2471
2472 3. **Security**
2473 * Store API keys securely in `.env`
2474 * Review the tools exposed by a server before allowing model-driven calls
2475 * Connect only to servers and executable commands you trust
2476
2477 ## Troubleshooting
2478
2479 ### Server Command Issues
2480
2481 The arguments after `cargo run --` must form a complete command. Interpreted server scripts need their runtime:
2482
2483 ```bash theme={null}
2484 # Correct
2485 cargo run -- python ./server/weather.py
2486 cargo run -- node ./server/build/index.js
2487
2488 # Incorrect: a Python script is not necessarily executable by itself
2489 cargo run -- ./server/weather.py
2490 ```
2491
2492 If a command cannot be found, use its absolute path or verify it is available in your `PATH`.
2493
2494 ### Environment File Issues
2495
2496 If you see `Failed to load env file`, ensure `.env` exists in the directory where you run the client.
2497
2498 If the model request reports a missing API key, confirm that `.env` contains:
2499
2500 ```text theme={null}
2501 ANTHROPIC_API_KEY=your-api-key-goes-here
2502 ```
2503
2504 ### Tool and Response Errors
2505
2506 * `Unable to list tools from server`: Verify the server starts successfully and communicates over stdio
2507 * `Tool call ... failed`: Verify the server tool's required arguments and environment variables
2508 * `Failed to serialize tool result`: Inspect the server's response for unsupported or malformed content
2509 </Tab>
2510</Tabs>
2380 .await;
2381
2382 let cleanup_result = client.cleanup().await;
2383
2384 result?;
2385 cleanup_result?;
2386
2387 Ok(())
2388}
2389```
2390
2391The entry point loads `.env`, treats all remaining command-line arguments as the server command, connects the client, starts the chat loop, and ensures cleanup runs before exiting.
2392
2393### Verify the Complete File
2394
2395Before running the client, confirm the items in `src/main.rs` are placed at the correct scope:
2396
2397* `new`, `connect_to_server`, `process_query`, `request_model`, `chat_loop`, and `cleanup` are methods inside the single `impl MCPClient` block.
2398* `main` and `convert_tools` are functions outside the `impl MCPClient` block.
2399
2400Rust does not require these items to appear in a particular order, but methods and free functions must be placed in the correct scope. Compare your file with the [complete `src/main.rs` example](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-rust/src/main.rs), then check that it compiles:
2401
2402```bash theme={null}
2403cargo fmt --check
2404cargo check
2405```
2406
2407## Running the Client
2408
2409Use `cargo run --` followed by the command you would normally use to start the MCP server:
2410
2411```bash theme={null}
2412# Python server
2413cargo run -- python path/to/server.py
2414
2415# Node.js server
2416cargo run -- node path/to/build/index.js
2417
2418# Executable server
2419cargo run -- path/to/server-binary
2420```
2421
2422Running bare `cargo run` without a server command prints the usage message and exits.
2423
2424> [!NOTE]
2425>
2426> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust), build the server first and then run a command similar to: `cargo run -- ../weather-server-rust/target/debug/weather`
2427
2428The client will:
2429
24301. Start and connect to the specified MCP server
24312. List the tools available from that server
24323. Start an interactive chat session where you can:
2433 * Enter queries
2434 * See tool executions
2435 * Get responses from Claude
2436
2437## How It Works
2438
2439When you submit a query:
2440
24411. The client sends your query and the server's available tools to Claude
24422. Claude decides which tools, if any, to use
24433. The client executes requested tools through the MCP session
24444. Tool results are sent back to Claude
24455. Claude provides a natural language response
24466. The response is displayed in the terminal
2447
2448## Best Practices
2449
24501. **Error Handling**
2451 * Add context to errors at process, MCP, model API, and serialization boundaries
2452 * Report individual query errors without terminating the interactive session
2453 * Validate server commands before running them
2454
24552. **Resource Management**
2456 * Always cancel the MCP session during cleanup
2457 * Ensure cleanup runs even when connection or chat-loop operations fail
2458 * Avoid starting a second server while a session is active
2459
24603. **Security**
2461 * Store API keys securely in `.env`
2462 * Review the tools exposed by a server before allowing model-driven calls
2463 * Connect only to servers and executable commands you trust
2464
2465## Troubleshooting
2466
2467### Server Command Issues
2468
2469The arguments after `cargo run --` must form a complete command. Interpreted server scripts need their runtime:
2470
2471```bash theme={null}
2472# Correct
2473cargo run -- python ./server/weather.py
2474cargo run -- node ./server/build/index.js
2475
2476# Incorrect: a Python script is not necessarily executable by itself
2477cargo run -- ./server/weather.py
2478```
2479
2480If a command cannot be found, use its absolute path or verify it is available in your `PATH`.
2481
2482### Environment File Issues
2483
2484If you see `Failed to load env file`, ensure `.env` exists in the directory where you run the client.
2485
2486If the model request reports a missing API key, confirm that `.env` contains:
2487
2488```text theme={null}
2489ANTHROPIC_API_KEY=your-api-key-goes-here
2490```
2491
2492### Tool and Response Errors
2493
2494* `Unable to list tools from server`: Verify the server starts successfully and communicates over stdio
2495* `Tool call ... failed`: Verify the server tool's required arguments and environment variables
2496* `Failed to serialize tool result`: Inspect the server's response for unsupported or malformed content
25112497
25122498## Next steps
25132499
2514<CardGroup cols={2}>
2515 <Card title="Example servers" icon="grid" href="/examples">
2516 Check out our gallery of official MCP servers and implementations
2517 </Card>
2518</CardGroup>
2500> **[Example servers](/examples)**
2501>
2502> Check out our gallery of official MCP servers and implementations
25192503
docs/2025-11-25/develop/build-server Changed · +2869 / -2937 lines
### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and setting up the instance ### Helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and setting up the instance ### Helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Logging in MCP Servers ### Best Practices ### System requirements ### Set up your environment ## Building your server ### Weather Service ### Create your Boot Application ### Running the server ## Testing your server with Claude for Desktop ## Testing your server with Java client ### Create an MCP Client manually ### Use MCP Client Boot Starter ## More Java MCP Server examples ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### System requirements ### Set up your environment ## Building your server ### Setting up the instance ### Weather API helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### System requirements ### Set up your environment ## Building your server ### Weather API helper functions ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and setting up constants ### Helper methods ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and constants ### Data structures ### Helper functions ### Implementing the Weather server and tools ### Implementing the ServerHandler ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and constants ### Data structures ### Helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop
The two sides of this change are more than 400 edits apart, too far apart to line up, so this is the differ's own diff of it and the words inside a line are not marked.
from line 8
88
99We'll build a server that exposes two tools: `get_alerts` and `get_forecast`. Then we'll connect the server to an MCP host (in this case, Claude for Desktop):
1010
11<Frame>
12 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/current-weather.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=dce7b2f8a06c20ba358e4bd2e75fa4c7" width="2780" height="1849" data-path="images/current-weather.png" />
13</Frame>
14
15<Note>
16 Servers can connect to any client. We've chosen Claude for Desktop here for simplicity, but we also have a guide on [building your own client](/docs/2025-11-25/develop/build-client).
17</Note>
11
12
13> [!NOTE]
14>
15> Servers can connect to any client. We've chosen Claude for Desktop here for simplicity, but we also have a guide on [building your own client](/docs/2025-11-25/develop/build-client).
1816
1917### Core MCP Concepts
2018
from line 24
2624
2725This tutorial will primarily focus on tools.
2826
29<Tabs>
30 <Tab title="Python">
31 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python)
32
33 ### Prerequisite knowledge
34
35 This quickstart assumes you have familiarity with:
36
37 * Python
38 * LLMs like Claude
39
40 ### Logging in MCP Servers
41
42 When implementing MCP servers, be careful about how you handle logging:
43
44 **For STDIO-based servers:** Never write to stdout. Writing to stdout will corrupt the JSON-RPC messages and break your server. The `print()` function writes to stdout by default, but can be used safely with `file=sys.stderr`.
45
46 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
47
48 ### Best Practices
49
50 * Use a logging library that writes to stderr or files.
51
52 ### Quick Examples
53
54 ```python theme={null}
55 import sys
56 import logging
57
58 # ❌ Bad (STDIO)
59 print("Processing request")
60
61 # ✅ Good (STDIO)
62 print("Processing request", file=sys.stderr)
63
64 # ✅ Good (STDIO)
65 logging.info("Processing request")
66 ```
67
68 ### System requirements
69
70 * Python 3.10 or higher installed.
71 * You must use the Python MCP SDK 1.2.0 or higher.
72
73 ### Set up your environment
74
75 First, let's install `uv` and set up our Python project and environment:
76
77 <CodeGroup>
78 ```bash macOS/Linux theme={null}
79 curl -LsSf https://astral.sh/uv/install.sh | sh
80 ```
81
82 ```powershell Windows theme={null}
83 powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"
84 ```
85 </CodeGroup>
86
87 Make sure to restart your terminal afterwards to ensure that the `uv` command gets picked up.
88
89 Now, let's create and set up our project:
90
91 <CodeGroup>
92 ```bash macOS/Linux theme={null}
93 # Create a new directory for our project
94 uv init weather
95 cd weather
96
97 # Create virtual environment and activate it
98 uv venv
99 source .venv/bin/activate
100
101 # Install dependencies
102 uv add "mcp[cli]" httpx
103
104 # Create our server file
105 touch weather.py
106 ```
107
108 ```powershell Windows theme={null}
109 # Create a new directory for our project
110 uv init weather
111 cd weather
112
113 # Create virtual environment and activate it
114 uv venv
115 .venv\Scripts\activate
116
117 # Install dependencies
118 uv add mcp[cli] httpx
119
120 # Create our server file
121 new-item weather.py
122 ```
123 </CodeGroup>
124
125 Now let's dive into building your server.
126
127 ## Building your server
128
129 ### Importing packages and setting up the instance
130
131 Add these to the top of your `weather.py`:
132
133 ```python theme={null}
134 from typing import Any
135
136 import httpx
137 from mcp.server.fastmcp import FastMCP
138
139 # Initialize FastMCP server
140 mcp = FastMCP("weather")
141
142 # Constants
143 NWS_API_BASE = "https://api.weather.gov"
144 USER_AGENT = "weather-app/1.0"
145 ```
146
147 The FastMCP class uses Python type hints and docstrings to automatically generate tool definitions, making it easy to create and maintain MCP tools.
148
149 ### Helper functions
150
151 Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
152
153 ```python theme={null}
154 async def make_nws_request(url: str) -> dict[str, Any] | None:
155 """Make a request to the NWS API with proper error handling."""
156 headers = {"User-Agent": USER_AGENT, "Accept": "application/geo+json"}
157 async with httpx.AsyncClient() as client:
158 try:
159 response = await client.get(url, headers=headers, timeout=30.0)
160 response.raise_for_status()
161 return response.json()
162 except Exception:
163 return None
164
165
166 def format_alert(feature: dict) -> str:
167 """Format an alert feature into a readable string."""
168 props = feature["properties"]
169 return f"""
170 Event: {props.get("event", "Unknown")}
171 Area: {props.get("areaDesc", "Unknown")}
172 Severity: {props.get("severity", "Unknown")}
173 Description: {props.get("description", "No description available")}
174 Instructions: {props.get("instruction", "No specific instructions provided")}
27**Python**
28
29Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python)
30
31### Prerequisite knowledge
32
33This quickstart assumes you have familiarity with:
34
35* Python
36* LLMs like Claude
37
38### Logging in MCP Servers
39
40When implementing MCP servers, be careful about how you handle logging:
41
42**For STDIO-based servers:** Never write to stdout. Writing to stdout will corrupt the JSON-RPC messages and break your server. The `print()` function writes to stdout by default, but can be used safely with `file=sys.stderr`.
43
44**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
45
46### Best Practices
47
48* Use a logging library that writes to stderr or files.
49
50### Quick Examples
51
52```python theme={null}
53import sys
54import logging
55
56# ❌ Bad (STDIO)
57print("Processing request")
58
59# ✅ Good (STDIO)
60print("Processing request", file=sys.stderr)
61
62# ✅ Good (STDIO)
63logging.info("Processing request")
64```
65
66### System requirements
67
68* Python 3.10 or higher installed.
69* You must use the Python MCP SDK 1.2.0 or higher.
70
71### Set up your environment
72
73First, let's install `uv` and set up our Python project and environment:
74
75```bash macOS/Linux theme={null}
76curl -LsSf https://astral.sh/uv/install.sh | sh
77```
78
79```powershell Windows theme={null}
80powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"
81```
82
83Make sure to restart your terminal afterwards to ensure that the `uv` command gets picked up.
84
85Now, let's create and set up our project:
86
87```bash macOS/Linux theme={null}
88# Create a new directory for our project
89uv init weather
90cd weather
91
92# Create virtual environment and activate it
93uv venv
94source .venv/bin/activate
95
96# Install dependencies
97uv add "mcp[cli]" httpx
98
99# Create our server file
100touch weather.py
101```
102
103```powershell Windows theme={null}
104# Create a new directory for our project
105uv init weather
106cd weather
107
108# Create virtual environment and activate it
109uv venv
110.venv\Scripts\activate
111
112# Install dependencies
113uv add mcp[cli] httpx
114
115# Create our server file
116new-item weather.py
117```
118
119Now let's dive into building your server.
120
121## Building your server
122
123### Importing packages and setting up the instance
124
125Add these to the top of your `weather.py`:
126
127```python theme={null}
128from typing import Any
129
130import httpx
131from mcp.server.fastmcp import FastMCP
132
133# Initialize FastMCP server
134mcp = FastMCP("weather")
135
136# Constants
137NWS_API_BASE = "https://api.weather.gov"
138USER_AGENT = "weather-app/1.0"
139```
140
141The FastMCP class uses Python type hints and docstrings to automatically generate tool definitions, making it easy to create and maintain MCP tools.
142
143### Helper functions
144
145Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
146
147```python theme={null}
148async def make_nws_request(url: str) -> dict[str, Any] | None:
149 """Make a request to the NWS API with proper error handling."""
150 headers = {"User-Agent": USER_AGENT, "Accept": "application/geo+json"}
151 async with httpx.AsyncClient() as client:
152 try:
153 response = await client.get(url, headers=headers, timeout=30.0)
154 response.raise_for_status()
155 return response.json()
156 except Exception:
157 return None
158
159
160def format_alert(feature: dict) -> str:
161 """Format an alert feature into a readable string."""
162 props = feature["properties"]
163 return f"""
164Event: {props.get("event", "Unknown")}
165Area: {props.get("areaDesc", "Unknown")}
166Severity: {props.get("severity", "Unknown")}
167Description: {props.get("description", "No description available")}
168Instructions: {props.get("instruction", "No specific instructions provided")}
169"""
170```
171
172### Implementing tool execution
173
174The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
175
176```python theme={null}
177@mcp.tool()
178async def get_alerts(state: str) -> str:
179 """Get weather alerts for a US state.
180
181 Args:
182 state: Two-letter US state code (e.g. CA, NY)
175183 """
176 ```
177
178 ### Implementing tool execution
179
180 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
181
182 ```python theme={null}
183 @mcp.tool()
184 async def get_alerts(state: str) -> str:
185 """Get weather alerts for a US state.
186
187 Args:
188 state: Two-letter US state code (e.g. CA, NY)
184 url = f"{NWS_API_BASE}/alerts/active/area/{state}"
185 data = await make_nws_request(url)
186
187 if not data or "features" not in data:
188 return "Unable to fetch alerts or no alerts found."
189
190 if not data["features"]:
191 return "No active alerts for this state."
192
193 alerts = [format_alert(feature) for feature in data["features"]]
194 return "\n---\n".join(alerts)
195
196
197@mcp.tool()
198async def get_forecast(latitude: float, longitude: float) -> str:
199 """Get weather forecast for a location.
200
201 Args:
202 latitude: Latitude of the location
203 longitude: Longitude of the location
204 """
205 # First get the forecast grid endpoint
206 points_url = f"{NWS_API_BASE}/points/{latitude},{longitude}"
207 points_data = await make_nws_request(points_url)
208
209 if not points_data:
210 return "Unable to fetch forecast data for this location."
211
212 # Get the forecast URL from the points response
213 forecast_url = points_data["properties"]["forecast"]
214 forecast_data = await make_nws_request(forecast_url)
215
216 if not forecast_data:
217 return "Unable to fetch detailed forecast."
218
219 # Format the periods into a readable forecast
220 periods = forecast_data["properties"]["periods"]
221 forecasts = []
222 for period in periods[:5]: # Only show next 5 periods
223 forecast = f"""
224{period["name"]}:
225Temperature: {period["temperature"]}°{period["temperatureUnit"]}
226Wind: {period["windSpeed"]} {period["windDirection"]}
227Forecast: {period["detailedForecast"]}
228"""
229 forecasts.append(forecast)
230
231 return "\n---\n".join(forecasts)
232```
233
234### Running the server
235
236Finally, let's initialize and run the server:
237
238```python theme={null}
239def main():
240 # Initialize and run the server
241 mcp.run(transport="stdio")
242
243
244if __name__ == "__main__":
245 main()
246```
247
248Your server is complete! Run `uv run weather.py` to start the MCP server, which will listen for messages from MCP hosts.
249
250Let's now test your server from an existing MCP host, Claude for Desktop.
251
252## Testing your server with Claude for Desktop
253
254> [!NOTE]
255>
256> Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
257
258First, make sure you have Claude for Desktop installed. [You can install the latest version
259here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
260
261We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
262
263For example, if you have [VS Code](https://code.visualstudio.com/) installed:
264
265```bash macOS/Linux theme={null}
266code ~/Library/Application\ Support/Claude/claude_desktop_config.json
267```
268
269```powershell Windows theme={null}
270code $env:AppData\Claude\claude_desktop_config.json
271```
272
273You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
274
275In this case, we'll add our single weather server like so:
276
277```json macOS/Linux theme={null}
278{
279 "mcpServers": {
280 "weather": {
281 "command": "uv",
282 "args": [
283 "--directory",
284 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather",
285 "run",
286 "weather.py"
287 ]
288 }
289 }
290}
291```
292
293```json Windows theme={null}
294{
295 "mcpServers": {
296 "weather": {
297 "command": "uv",
298 "args": [
299 "--directory",
300 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather",
301 "run",
302 "weather.py"
303 ]
304 }
305 }
306}
307```
308
309> [!WARNING]
310>
311> You may need to put the full path to the `uv` executable in the `command` field. You can get this by running `which uv` on macOS/Linux or `where uv` on Windows.
312
313> [!NOTE]
314>
315> Make sure you pass in the absolute path to your server. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
316
317This tells Claude for Desktop:
318
3191. There's an MCP server named "weather"
3202. To launch it by running `uv --directory /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather run weather.py`
321
322Save the file, and restart **Claude for Desktop**.
323
324**TypeScript**
325
326Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript)
327
328### Prerequisite knowledge
329
330This quickstart assumes you have familiarity with:
331
332* TypeScript
333* LLMs like Claude
334
335### Logging in MCP Servers
336
337When implementing MCP servers, be careful about how you handle logging:
338
339**For STDIO-based servers:** Never use `console.log()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
340
341**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
342
343### Best Practices
344
345* Use `console.error()` which writes to stderr, or use a logging library that writes to stderr or files.
346
347### Quick Examples
348
349```javascript theme={null}
350// ❌ Bad (STDIO)
351console.log("Server started");
352
353// ✅ Good (STDIO)
354console.error("Server started"); // stderr is safe
355```
356
357### System requirements
358
359For TypeScript, make sure you have the latest version of Node installed.
360
361### Set up your environment
362
363First, let's install Node.js and npm if you haven't already. You can download them from [nodejs.org](https://nodejs.org/).
364Verify your Node.js installation:
365
366```bash theme={null}
367node --version
368npm --version
369```
370
371For this tutorial, you'll need Node.js version 16 or higher.
372
373Now, let's create and set up our project:
374
375```bash macOS/Linux theme={null}
376# Create a new directory for our project
377mkdir weather
378cd weather
379
380# Initialize a new npm project
381npm init -y
382
383# Install dependencies
384npm install @modelcontextprotocol/sdk zod@3
385npm install -D @types/node typescript
386
387# Create our files
388mkdir src
389touch src/index.ts
390```
391
392```powershell Windows theme={null}
393# Create a new directory for our project
394md weather
395cd weather
396
397# Initialize a new npm project
398npm init -y
399
400# Install dependencies
401npm install @modelcontextprotocol/sdk zod@3
402npm install -D @types/node typescript
403
404# Create our files
405md src
406new-item src\index.ts
407```
408
409Update your package.json to add type: "module" and a build script:
410
411```json package.json theme={null}
412{
413 "type": "module",
414 "bin": {
415 "weather": "./build/index.js"
416 },
417 "scripts": {
418 "build": "tsc && chmod 755 build/index.js"
419 },
420 "files": ["build"]
421}
422```
423
424Create a `tsconfig.json` in the root of your project:
425
426```json tsconfig.json theme={null}
427{
428 "compilerOptions": {
429 "target": "ES2022",
430 "module": "Node16",
431 "moduleResolution": "Node16",
432 "outDir": "./build",
433 "rootDir": "./src",
434 "strict": true,
435 "esModuleInterop": true,
436 "skipLibCheck": true,
437 "forceConsistentCasingInFileNames": true
438 },
439 "include": ["src/**/*"],
440 "exclude": ["node_modules"]
441}
442```
443
444Now let's dive into building your server.
445
446## Building your server
447
448### Importing packages and setting up the instance
449
450Add these to the top of your `src/index.ts`:
451
452```typescript theme={null}
453import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
454import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
455import { z } from "zod";
456
457const NWS_API_BASE = "https://api.weather.gov";
458const USER_AGENT = "weather-app/1.0";
459
460// Create server instance
461const server = new McpServer({
462 name: "weather",
463 version: "1.0.0",
464});
465```
466
467### Helper functions
468
469Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
470
471```typescript theme={null}
472// Helper function for making NWS API requests
473async function makeNWSRequest<T>(url: string): Promise<T | null> {
474 const headers = {
475 "User-Agent": USER_AGENT,
476 Accept: "application/geo+json",
477 };
478
479 try {
480 const response = await fetch(url, { headers });
481 if (!response.ok) {
482 throw new Error(`HTTP error! status: ${response.status}`);
483 }
484 return (await response.json()) as T;
485 } catch (error) {
486 console.error("Error making NWS request:", error);
487 return null;
488 }
489}
490
491interface AlertFeature {
492 properties: {
493 event?: string;
494 areaDesc?: string;
495 severity?: string;
496 status?: string;
497 headline?: string;
498 };
499}
500
501// Format alert data
502function formatAlert(feature: AlertFeature): string {
503 const props = feature.properties;
504 return [
505 `Event: ${props.event || "Unknown"}`,
506 `Area: ${props.areaDesc || "Unknown"}`,
507 `Severity: ${props.severity || "Unknown"}`,
508 `Status: ${props.status || "Unknown"}`,
509 `Headline: ${props.headline || "No headline"}`,
510 "---",
511 ].join("\n");
512}
513
514interface ForecastPeriod {
515 name?: string;
516 temperature?: number;
517 temperatureUnit?: string;
518 windSpeed?: string;
519 windDirection?: string;
520 shortForecast?: string;
521}
522
523interface AlertsResponse {
524 features: AlertFeature[];
525}
526
527interface PointsResponse {
528 properties: {
529 forecast?: string;
530 };
531}
532
533interface ForecastResponse {
534 properties: {
535 periods: ForecastPeriod[];
536 };
537}
538```
539
540### Implementing tool execution
541
542The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
543
544```typescript theme={null}
545// Register weather tools
546
547server.registerTool(
548 "get_alerts",
549 {
550 description: "Get weather alerts for a state",
551 inputSchema: {
552 state: z
553 .string()
554 .length(2)
555 .describe("Two-letter state code (e.g. CA, NY)"),
556 },
557 },
558 async ({ state }) => {
559 const stateCode = state.toUpperCase();
560 const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`;
561 const alertsData = await makeNWSRequest<AlertsResponse>(alertsUrl);
562
563 if (!alertsData) {
564 return {
565 content: [
566 {
567 type: "text",
568 text: "Failed to retrieve alerts data",
569 },
570 ],
571 };
572 }
573
574 const features = alertsData.features || [];
575 if (!features.length) {
576 return {
577 content: [
578 {
579 type: "text",
580 text: `No active alerts for ${stateCode}`,
581 },
582 ],
583 };
584 }
585
586 const formattedAlerts = features.map(formatAlert);
587 const alertsText = `Active alerts for ${stateCode}:\n\n${formattedAlerts.join("\n")}`;
588
589 return {
590 content: [
591 {
592 type: "text",
593 text: alertsText,
594 },
595 ],
596 };
597 },
598);
599
600server.registerTool(
601 "get_forecast",
602 {
603 description: "Get weather forecast for a location",
604 inputSchema: {
605 latitude: z
606 .number()
607 .min(-90)
608 .max(90)
609 .describe("Latitude of the location"),
610 longitude: z
611 .number()
612 .min(-180)
613 .max(180)
614 .describe("Longitude of the location"),
615 },
616 },
617 async ({ latitude, longitude }) => {
618 // Get grid point data
619 const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`;
620 const pointsData = await makeNWSRequest<PointsResponse>(pointsUrl);
621
622 if (!pointsData) {
623 return {
624 content: [
625 {
626 type: "text",
627 text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`,
628 },
629 ],
630 };
631 }
632
633 const forecastUrl = pointsData.properties?.forecast;
634 if (!forecastUrl) {
635 return {
636 content: [
637 {
638 type: "text",
639 text: "Failed to get forecast URL from grid point data",
640 },
641 ],
642 };
643 }
644
645 // Get forecast data
646 const forecastData = await makeNWSRequest<ForecastResponse>(forecastUrl);
647 if (!forecastData) {
648 return {
649 content: [
650 {
651 type: "text",
652 text: "Failed to retrieve forecast data",
653 },
654 ],
655 };
656 }
657
658 const periods = forecastData.properties?.periods || [];
659 if (periods.length === 0) {
660 return {
661 content: [
662 {
663 type: "text",
664 text: "No forecast periods available",
665 },
666 ],
667 };
668 }
669
670 // Format forecast periods
671 const formattedForecast = periods.map((period: ForecastPeriod) =>
672 [
673 `${period.name || "Unknown"}:`,
674 `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
675 `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
676 `${period.shortForecast || "No forecast available"}`,
677 "---",
678 ].join("\n"),
679 );
680
681 const forecastText = `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join("\n")}`;
682
683 return {
684 content: [
685 {
686 type: "text",
687 text: forecastText,
688 },
689 ],
690 };
691 },
692);
693```
694
695### Running the server
696
697Finally, implement the main function to run the server:
698
699```typescript theme={null}
700async function main() {
701 const transport = new StdioServerTransport();
702 await server.connect(transport);
703 console.error("Weather MCP Server running on stdio");
704}
705
706main().catch((error) => {
707 console.error("Fatal error in main():", error);
708 process.exit(1);
709});
710```
711
712Make sure to run `npm run build` to build your server! This is a very important step in getting your server to connect.
713
714Let's now test your server from an existing MCP host, Claude for Desktop.
715
716## Testing your server with Claude for Desktop
717
718> [!NOTE]
719>
720> Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
721
722First, make sure you have Claude for Desktop installed. [You can install the latest version
723here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
724
725We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
726
727For example, if you have [VS Code](https://code.visualstudio.com/) installed:
728
729```bash macOS/Linux theme={null}
730code ~/Library/Application\ Support/Claude/claude_desktop_config.json
731```
732
733```powershell Windows theme={null}
734code $env:AppData\Claude\claude_desktop_config.json
735```
736
737You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
738
739In this case, we'll add our single weather server like so:
740
741```json macOS/Linux theme={null}
742{
743 "mcpServers": {
744 "weather": {
745 "command": "node",
746 "args": ["/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js"]
747 }
748 }
749}
750```
751
752```json Windows theme={null}
753{
754 "mcpServers": {
755 "weather": {
756 "command": "node",
757 "args": ["C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\index.js"]
758 }
759 }
760}
761```
762
763This tells Claude for Desktop:
764
7651. There's an MCP server named "weather"
7662. Launch it by running `node /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js`
767
768Save the file, and restart **Claude for Desktop**.
769
770**Java**
771
772> [!NOTE]
773>
774> This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
775> To learn how to create sync and async MCP Servers, manually, consult the [Java SDK Server](https://java.sdk.modelcontextprotocol.io/) documentation.
776
777Let's get started with building our weather server!
778[You can find the complete code for what we'll be building here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-stdio-server)
779
780For more information, see the [MCP Server Boot Starter](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html) reference documentation.
781For manual MCP Server implementation, refer to the [MCP Server Java SDK documentation](https://java.sdk.modelcontextprotocol.io/).
782
783### Logging in MCP Servers
784
785When implementing MCP servers, be careful about how you handle logging:
786
787**For STDIO-based servers:** Never use `System.out.println()` or `System.out.print()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
788
789**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
790
791### Best Practices
792
793* Use a logging library that writes to stderr or files.
794* Ensure any configured logging library will not write to stdout.
795
796### System requirements
797
798* Java 17 or higher installed.
799* [Spring Boot 3.3.x](https://docs.spring.io/spring-boot/installing.html) or higher
800
801### Set up your environment
802
803Use the [Spring Initializer](https://start.spring.io/) to bootstrap the project.
804
805You will need to add the following dependencies:
806
807```xml Maven theme={null}
808<dependencies>
809 <dependency>
810 <groupId>org.springframework.ai</groupId>
811 <artifactId>spring-ai-starter-mcp-server</artifactId>
812 </dependency>
813
814 <dependency>
815 <groupId>org.springframework</groupId>
816 <artifactId>spring-web</artifactId>
817 </dependency>
818</dependencies>
819```
820
821```groovy Gradle theme={null}
822dependencies {
823 implementation platform("org.springframework.ai:spring-ai-starter-mcp-server")
824 implementation platform("org.springframework:spring-web")
825}
826```
827
828Then configure your application by setting the application properties:
829
830```bash application.properties theme={null}
831spring.main.bannerMode=off
832logging.pattern.console=
833```
834
835```yaml application.yml theme={null}
836logging:
837 pattern:
838 console:
839spring:
840 main:
841 banner-mode: off
842```
843
844The [Server Configuration Properties](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html#_configuration_properties) documents all available properties.
845
846Now let's dive into building your server.
847
848## Building your server
849
850### Weather Service
851
852Let's implement a [WeatherService.java](https://github.com/spring-projects/spring-ai-examples/blob/main/model-context-protocol/weather/starter-stdio-server/src/main/java/org/springframework/ai/mcp/sample/server/WeatherService.java) that uses a REST client to query the data from the National Weather Service API:
853
854```java theme={null}
855@Service
856public class WeatherService {
857
858 private final RestClient restClient;
859
860 public WeatherService() {
861 this.restClient = RestClient.builder()
862 .baseUrl("https://api.weather.gov")
863 .defaultHeader("Accept", "application/geo+json")
864 .defaultHeader("User-Agent", "WeatherApiClient/1.0 ([email protected])")
865 .build();
866 }
867
868 @Tool(description = "Get weather forecast for a specific latitude/longitude")
869 public String getWeatherForecastByLocation(
870 double latitude, // Latitude coordinate
871 double longitude // Longitude coordinate
872 ) {
873 // Returns detailed forecast including:
874 // - Temperature and unit
875 // - Wind speed and direction
876 // - Detailed forecast description
877 }
878
879 @Tool(description = "Get weather alerts for a US state")
880 public String getAlerts(
881 @ToolParam(description = "Two-letter US state code (e.g. CA, NY)") String state
882 ) {
883 // Returns active alerts including:
884 // - Event type
885 // - Affected area
886 // - Severity
887 // - Description
888 // - Safety instructions
889 }
890
891 // ......
892}
893```
894
895The `@Service` annotation will auto-register the service in your application context.
896The Spring AI `@Tool` annotation makes it easy to create and maintain MCP tools.
897
898The auto-configuration will automatically register these tools with the MCP server.
899
900### Create your Boot Application
901
902```java theme={null}
903@SpringBootApplication
904public class McpServerApplication {
905
906 public static void main(String[] args) {
907 SpringApplication.run(McpServerApplication.class, args);
908 }
909
910 @Bean
911 public ToolCallbackProvider weatherTools(WeatherService weatherService) {
912 return MethodToolCallbackProvider.builder().toolObjects(weatherService).build();
913 }
914}
915```
916
917Uses the `MethodToolCallbackProvider` utils to convert the `@Tools` into actionable callbacks used by the MCP server.
918
919### Running the server
920
921Finally, let's build the server:
922
923```bash theme={null}
924./mvnw clean install
925```
926
927This will generate an `mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar` file within the `target` folder.
928
929Let's now test your server from an existing MCP host, Claude for Desktop.
930
931## Testing your server with Claude for Desktop
932
933> [!NOTE]
934>
935> Claude for Desktop is not yet available on Linux.
936
937First, make sure you have Claude for Desktop installed.
938[You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
939
940We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
941To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
942Make sure to create the file if it doesn't exist.
943
944For example, if you have [VS Code](https://code.visualstudio.com/) installed:
945
946```bash macOS/Linux theme={null}
947code ~/Library/Application\ Support/Claude/claude_desktop_config.json
948```
949
950```powershell Windows theme={null}
951code $env:AppData\Claude\claude_desktop_config.json
952```
953
954You'll then add your servers in the `mcpServers` key.
955The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
956
957In this case, we'll add our single weather server like so:
958
959```json macOS/Linux theme={null}
960{
961 "mcpServers": {
962 "spring-ai-mcp-weather": {
963 "command": "java",
964 "args": [
965 "-Dspring.ai.mcp.server.stdio=true",
966 "-jar",
967 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
968 ]
969 }
970 }
971}
972```
973
974```json Windows theme={null}
975{
976 "mcpServers": {
977 "spring-ai-mcp-weather": {
978 "command": "java",
979 "args": [
980 "-Dspring.ai.mcp.server.transport=STDIO",
981 "-jar",
982 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
983 ]
984 }
985 }
986}
987```
988
989> [!NOTE]
990>
991> Make sure you pass in the absolute path to your server.
992
993This tells Claude for Desktop:
994
9951. There's an MCP server named "my-weather-server"
9962. To launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar`
997
998Save the file, and restart **Claude for Desktop**.
999
1000## Testing your server with Java client
1001
1002### Create an MCP Client manually
1003
1004Use the `McpClient` to connect to the server:
1005
1006```java theme={null}
1007var stdioParams = ServerParameters.builder("java")
1008 .args("-jar", "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar")
1009 .build();
1010
1011var stdioTransport = new StdioClientTransport(stdioParams);
1012
1013var mcpClient = McpClient.sync(stdioTransport).build();
1014
1015mcpClient.initialize();
1016
1017ListToolsResult toolsList = mcpClient.listTools();
1018
1019CallToolResult weather = mcpClient.callTool(
1020 new CallToolRequest("getWeatherForecastByLocation",
1021 Map.of("latitude", "47.6062", "longitude", "-122.3321")));
1022
1023CallToolResult alert = mcpClient.callTool(
1024 new CallToolRequest("getAlerts", Map.of("state", "NY")));
1025
1026mcpClient.closeGracefully();
1027```
1028
1029### Use MCP Client Boot Starter
1030
1031Create a new boot starter application using the `spring-ai-starter-mcp-client` dependency:
1032
1033```xml theme={null}
1034<dependency>
1035 <groupId>org.springframework.ai</groupId>
1036 <artifactId>spring-ai-starter-mcp-client</artifactId>
1037</dependency>
1038```
1039
1040and set the `spring.ai.mcp.client.stdio.servers-configuration` property to point to your `claude_desktop_config.json`.
1041You can reuse the existing Anthropic Desktop configuration:
1042
1043```properties theme={null}
1044spring.ai.mcp.client.stdio.servers-configuration=file:PATH/TO/claude_desktop_config.json
1045```
1046
1047When you start your client application, the auto-configuration will automatically create MCP clients from the claude\_desktop\_config.json.
1048
1049For more information, see the [MCP Client Boot Starters](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-client-boot-starter-docs.html) reference documentation.
1050
1051## More Java MCP Server examples
1052
1053The [starter-webflux-server](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-webflux-server) demonstrates how to create an MCP server using SSE transport.
1054It showcases how to define and register MCP Tools, Resources, and Prompts, using the Spring Boot's auto-configuration capabilities.
1055
1056**Kotlin**
1057
1058Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/weather-stdio-server)
1059
1060### Prerequisite knowledge
1061
1062This quickstart assumes you have familiarity with:
1063
1064* Kotlin
1065* LLMs like Claude
1066
1067### Logging in MCP Servers
1068
1069When implementing MCP servers, be careful about how you handle logging:
1070
1071**For STDIO-based servers:** Never use `println()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1072
1073**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1074
1075### Best Practices
1076
1077* Use a logging library that writes to stderr or files.
1078
1079### System requirements
1080
1081* JDK 11 or higher installed.
1082
1083### Set up your environment
1084
1085First, let's install `java` and `gradle` if you haven't already.
1086You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1087Verify your `java` installation:
1088
1089```bash theme={null}
1090java --version
1091```
1092
1093Now, let's create and set up your project:
1094
1095```bash macOS/Linux theme={null}
1096# Create a new directory for our project
1097mkdir weather
1098cd weather
1099
1100# Initialize a new kotlin project
1101gradle init
1102```
1103
1104```powershell Windows theme={null}
1105# Create a new directory for our project
1106md weather
1107cd weather
1108
1109# Initialize a new kotlin project
1110gradle init
1111```
1112
1113After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1114
1115Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1116
1117After creating the project, replace the contents of your `build.gradle.kts` with:
1118
1119```kotlin build.gradle.kts theme={null}
1120// Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1121val mcpVersion = "0.9.0"
1122val ktorVersion = "3.2.3"
1123val slf4jVersion = "2.0.17"
1124
1125plugins {
1126 kotlin("jvm") version "2.3.20"
1127 kotlin("plugin.serialization") version "2.3.20"
1128 id("com.gradleup.shadow") version "8.3.9"
1129 application
1130}
1131
1132application {
1133 mainClass.set("MainKt")
1134}
1135
1136dependencies {
1137 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1138 implementation("io.ktor:ktor-client-content-negotiation:$ktorVersion")
1139 implementation("io.ktor:ktor-serialization-kotlinx-json:$ktorVersion")
1140 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1141 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1142}
1143```
1144
1145Verify that everything is set up correctly:
1146
1147```bash theme={null}
1148./gradlew build
1149```
1150
1151Now let's dive into building your server.
1152
1153## Building your server
1154
1155### Setting up the instance
1156
1157Add a server initialization function:
1158
1159```kotlin theme={null}
1160fun runMcpServer() {
1161 val server = Server(
1162 Implementation(
1163 name = "weather",
1164 version = "1.0.0",
1165 ),
1166 ServerOptions(
1167 capabilities = ServerCapabilities(tools = ServerCapabilities.Tools(listChanged = true)),
1168 ),
1169 )
1170
1171 // register tools on server here
1172
1173 val transport = StdioServerTransport(
1174 System.`in`.asInput(),
1175 System.out.asSink().buffered(),
1176 )
1177
1178 runBlocking {
1179 val session = server.createSession(transport)
1180 val done = Job()
1181 session.onClose {
1182 done.complete()
1183 }
1184 done.join()
1185 }
1186}
1187```
1188
1189### Weather API helper functions
1190
1191Next, let's add functions and data classes for querying and converting responses from the National Weather Service API:
1192
1193```kotlin theme={null}
1194val httpClient = HttpClient(CIO) {
1195 defaultRequest {
1196 url("https://api.weather.gov")
1197 headers {
1198 append("Accept", "application/geo+json")
1199 append("User-Agent", "WeatherApiClient/1.0")
1200 }
1201 contentType(ContentType.Application.Json)
1202 }
1203 install(ContentNegotiation) {
1204 json(Json { ignoreUnknownKeys = true })
1205 }
1206}
1207
1208// Extension function to fetch weather alerts for a given state
1209suspend fun HttpClient.getAlerts(state: String): List<String> {
1210 val alerts = this.get("/alerts/active/area/$state").body<AlertsResponse>()
1211 return alerts.features.map { feature ->
1891212 """
190 url = f"{NWS_API_BASE}/alerts/active/area/{state}"
191 data = await make_nws_request(url)
192
193 if not data or "features" not in data:
194 return "Unable to fetch alerts or no alerts found."
195
196 if not data["features"]:
197 return "No active alerts for this state."
198
199 alerts = [format_alert(feature) for feature in data["features"]]
200 return "\n---\n".join(alerts)
201
202
203 @mcp.tool()
204 async def get_forecast(latitude: float, longitude: float) -> str:
205 """Get weather forecast for a location.
206
207 Args:
208 latitude: Latitude of the location
209 longitude: Longitude of the location
1213 Event: ${feature.properties.event}
1214 Area: ${feature.properties.areaDesc}
1215 Severity: ${feature.properties.severity}
1216 Status: ${feature.properties.status}
1217 Headline: ${feature.properties.headline}
1218 """.trimIndent()
1219 }
1220}
1221
1222// Extension function to fetch forecast information for given latitude and longitude
1223suspend fun HttpClient.getForecast(latitude: Double, longitude: Double): List<String> {
1224 val points = this.get("/points/$latitude,$longitude").body<PointsResponse>()
1225 val forecastUrl = points.properties.forecast ?: error("No forecast URL available")
1226 val forecast = this.get(forecastUrl).body<ForecastResponse>()
1227 return forecast.properties.periods.map { period ->
2101228 """
211 # First get the forecast grid endpoint
212 points_url = f"{NWS_API_BASE}/points/{latitude},{longitude}"
213 points_data = await make_nws_request(points_url)
214
215 if not points_data:
216 return "Unable to fetch forecast data for this location."
217
218 # Get the forecast URL from the points response
219 forecast_url = points_data["properties"]["forecast"]
220 forecast_data = await make_nws_request(forecast_url)
221
222 if not forecast_data:
223 return "Unable to fetch detailed forecast."
224
225 # Format the periods into a readable forecast
226 periods = forecast_data["properties"]["periods"]
227 forecasts = []
228 for period in periods[:5]: # Only show next 5 periods
229 forecast = f"""
230 {period["name"]}:
231 Temperature: {period["temperature"]}°{period["temperatureUnit"]}
232 Wind: {period["windSpeed"]} {period["windDirection"]}
233 Forecast: {period["detailedForecast"]}
234 """
235 forecasts.append(forecast)
236
237 return "\n---\n".join(forecasts)
238 ```
239
240 ### Running the server
241
242 Finally, let's initialize and run the server:
243
244 ```python theme={null}
245 def main():
246 # Initialize and run the server
247 mcp.run(transport="stdio")
248
249
250 if __name__ == "__main__":
251 main()
252 ```
253
254 Your server is complete! Run `uv run weather.py` to start the MCP server, which will listen for messages from MCP hosts.
255
256 Let's now test your server from an existing MCP host, Claude for Desktop.
257
258 ## Testing your server with Claude for Desktop
259
260 <Note>
261 Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
262 </Note>
263
264 First, make sure you have Claude for Desktop installed. [You can install the latest version
265 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
266
267 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
268
269 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
270
271 <CodeGroup>
272 ```bash macOS/Linux theme={null}
273 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
274 ```
275
276 ```powershell Windows theme={null}
277 code $env:AppData\Claude\claude_desktop_config.json
278 ```
279 </CodeGroup>
280
281 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
282
283 In this case, we'll add our single weather server like so:
284
285 <CodeGroup>
286 ```json macOS/Linux theme={null}
287 {
288 "mcpServers": {
289 "weather": {
290 "command": "uv",
291 "args": [
292 "--directory",
293 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather",
294 "run",
295 "weather.py"
296 ]
297 }
1229 ${period.name}:
1230 Temperature: ${period.temperature}°${period.temperatureUnit}
1231 Wind: ${period.windSpeed} ${period.windDirection}
1232 ${period.shortForecast}
1233 """.trimIndent()
1234 }
1235}
1236
1237@Serializable
1238data class PointsResponse(val properties: PointsProperties)
1239
1240@Serializable
1241data class PointsProperties(val forecast: String? = null)
1242
1243@Serializable
1244data class ForecastResponse(val properties: ForecastProperties)
1245
1246@Serializable
1247data class ForecastProperties(val periods: List<ForecastPeriod> = emptyList())
1248
1249@Serializable
1250data class ForecastPeriod(
1251 val name: String? = null,
1252 val temperature: Int? = null,
1253 val temperatureUnit: String? = null,
1254 val windSpeed: String? = null,
1255 val windDirection: String? = null,
1256 val shortForecast: String? = null,
1257)
1258
1259@Serializable
1260data class AlertsResponse(val features: List<AlertFeature> = emptyList())
1261
1262@Serializable
1263data class AlertFeature(val properties: AlertProperties)
1264
1265@Serializable
1266data class AlertProperties(
1267 val event: String? = null,
1268 val areaDesc: String? = null,
1269 val severity: String? = null,
1270 val status: String? = null,
1271 val headline: String? = null,
1272)
1273```
1274
1275### Implementing tool execution
1276
1277The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
1278
1279```kotlin theme={null}
1280// Register weather tools
1281
1282server.addTool(
1283 name = "get_alerts",
1284 description = "Get weather alerts for a US state. Input is a two-letter US state code (e.g. CA, NY)",
1285 inputSchema = ToolSchema(
1286 properties = buildJsonObject {
1287 putJsonObject("state") {
1288 put("type", "string")
1289 put("description", "Two-letter US state code (e.g. CA, NY)")
1290 }
1291 },
1292 required = listOf("state"),
1293 ),
1294) { request ->
1295 val state = request.arguments?.get("state")?.jsonPrimitive?.content
1296 ?: return@addTool CallToolResult(
1297 content = listOf(TextContent("The 'state' parameter is required.")),
1298 )
1299
1300 val alerts = httpClient.getAlerts(state)
1301 CallToolResult(content = alerts.map { TextContent(it) })
1302}
1303
1304server.addTool(
1305 name = "get_forecast",
1306 description = "Get weather forecast for a location. Note: only US locations are supported by the NWS API.",
1307 inputSchema = ToolSchema(
1308 properties = buildJsonObject {
1309 putJsonObject("latitude") {
1310 put("type", "number")
1311 put("description", "Latitude of the location")
1312 }
1313 putJsonObject("longitude") {
1314 put("type", "number")
1315 put("description", "Longitude of the location")
1316 }
1317 },
1318 required = listOf("latitude", "longitude"),
1319 ),
1320) { request ->
1321 val latitude = request.arguments?.get("latitude")?.jsonPrimitive?.doubleOrNull
1322 val longitude = request.arguments?.get("longitude")?.jsonPrimitive?.doubleOrNull
1323 if (latitude == null || longitude == null) {
1324 return@addTool CallToolResult(
1325 content = listOf(TextContent("The 'latitude' and 'longitude' parameters are required.")),
1326 )
1327 }
1328
1329 val forecast = httpClient.getForecast(latitude, longitude)
1330 CallToolResult(content = forecast.map { TextContent(it) })
1331}
1332```
1333
1334### Running the server
1335
1336Finally, implement the main function to run the server:
1337
1338```kotlin theme={null}
1339fun main() = runMcpServer()
1340```
1341
1342You can run the server directly during development:
1343
1344```bash theme={null}
1345./gradlew run
1346```
1347
1348For production use, build the shadow JAR:
1349
1350```bash theme={null}
1351./gradlew build
1352java -jar build/libs/weather-0.1.0-all.jar
1353```
1354
1355Let's now test your server from an existing MCP host, Claude for Desktop.
1356
1357## Testing your server with Claude for Desktop
1358
1359> [!NOTE]
1360>
1361> Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
1362
1363First, make sure you have Claude for Desktop installed. [You can install the latest version
1364here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1365
1366We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
1367To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
1368Make sure to create the file if it doesn't exist.
1369
1370For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1371
1372```bash macOS/Linux theme={null}
1373code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1374```
1375
1376```powershell Windows theme={null}
1377code $env:AppData\Claude\claude_desktop_config.json
1378```
1379
1380You'll then add your servers in the `mcpServers` key.
1381The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1382
1383In this case, we'll add our single weather server like so:
1384
1385```json macOS/Linux theme={null}
1386{
1387 "mcpServers": {
1388 "weather": {
1389 "command": "java",
1390 "args": [
1391 "-jar",
1392 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar"
1393 ]
1394 }
1395 }
1396}
1397```
1398
1399```json Windows theme={null}
1400{
1401 "mcpServers": {
1402 "weather": {
1403 "command": "java",
1404 "args": [
1405 "-jar",
1406 "C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\libs\\weather-0.1.0-all.jar"
1407 ]
1408 }
1409 }
1410}
1411```
1412
1413This tells Claude for Desktop:
1414
14151. There's an MCP server named "weather"
14162. Launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar`
1417
1418Save the file, and restart **Claude for Desktop**.
1419
1420**C#**
1421
1422Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartWeatherServer)
1423
1424### Prerequisite knowledge
1425
1426This quickstart assumes you have familiarity with:
1427
1428* C#
1429* LLMs like Claude
1430* .NET 8 or higher
1431
1432### Logging in MCP Servers
1433
1434When implementing MCP servers, be careful about how you handle logging:
1435
1436**For STDIO-based servers:** Never use `Console.WriteLine()` or `Console.Write()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
1437
1438**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1439
1440### Best Practices
1441
1442* Use a logging library that writes to stderr or files.
1443
1444### System requirements
1445
1446* [.NET 8 SDK](https://dotnet.microsoft.com/download/dotnet/8.0) or higher installed.
1447
1448### Set up your environment
1449
1450First, let's install `dotnet` if you haven't already. You can download `dotnet` from [official Microsoft .NET website](https://dotnet.microsoft.com/download/). Verify your `dotnet` installation:
1451
1452```bash theme={null}
1453dotnet --version
1454```
1455
1456Now, let's create and set up your project:
1457
1458```bash macOS/Linux theme={null}
1459# Create a new directory for our project
1460mkdir weather
1461cd weather
1462# Initialize a new C# project
1463dotnet new console
1464```
1465
1466```powershell Windows theme={null}
1467# Create a new directory for our project
1468mkdir weather
1469cd weather
1470# Initialize a new C# project
1471dotnet new console
1472```
1473
1474After running `dotnet new console`, you will be presented with a new C# project.
1475You can open the project in your favorite IDE, such as [Visual Studio](https://visualstudio.microsoft.com/) or [Rider](https://www.jetbrains.com/rider/).
1476Alternatively, you can create a C# application using the [Visual Studio project wizard](https://learn.microsoft.com/en-us/visualstudio/get-started/csharp/tutorial-console?view=vs-2022).
1477After creating the project, add NuGet package for the Model Context Protocol SDK and hosting:
1478
1479```bash theme={null}
1480# Add the Model Context Protocol SDK NuGet package
1481dotnet add package ModelContextProtocol --prerelease
1482# Add the .NET Hosting NuGet package
1483dotnet add package Microsoft.Extensions.Hosting
1484```
1485
1486Now let’s dive into building your server.
1487
1488## Building your server
1489
1490Open the `Program.cs` file in your project and replace its contents with the following code:
1491
1492```csharp theme={null}
1493using Microsoft.Extensions.DependencyInjection;
1494using Microsoft.Extensions.Hosting;
1495using ModelContextProtocol;
1496using System.Net.Http.Headers;
1497
1498var builder = Host.CreateEmptyApplicationBuilder(settings: null);
1499
1500builder.Services.AddMcpServer()
1501 .WithStdioServerTransport()
1502 .WithToolsFromAssembly();
1503
1504builder.Services.AddSingleton(_ =>
1505{
1506 var client = new HttpClient() { BaseAddress = new Uri("https://api.weather.gov") };
1507 client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("weather-tool", "1.0"));
1508 return client;
1509});
1510
1511var app = builder.Build();
1512
1513await app.RunAsync();
1514```
1515
1516> [!NOTE]
1517>
1518> When creating the `ApplicationHostBuilder`, ensure you use `CreateEmptyApplicationBuilder` instead of `CreateDefaultBuilder`. This ensures that the server does not write any additional messages to the console. This is only necessary for servers using STDIO transport.
1519
1520This code sets up a basic console application that uses the Model Context Protocol SDK to create an MCP server with standard I/O transport.
1521
1522### Weather API helper functions
1523
1524Create an extension class for `HttpClient` which helps simplify JSON request handling:
1525
1526```csharp theme={null}
1527using System.Text.Json;
1528
1529internal static class HttpClientExt
1530{
1531 public static async Task<JsonDocument> ReadJsonDocumentAsync(this HttpClient client, string requestUri)
1532 {
1533 using var response = await client.GetAsync(requestUri);
1534 response.EnsureSuccessStatusCode();
1535 return await JsonDocument.ParseAsync(await response.Content.ReadAsStreamAsync());
1536 }
1537}
1538```
1539
1540Next, define a class with the tool execution handlers for querying and converting responses from the National Weather Service API:
1541
1542```csharp theme={null}
1543using ModelContextProtocol.Server;
1544using System.ComponentModel;
1545using System.Globalization;
1546using System.Text.Json;
1547
1548namespace QuickstartWeatherServer.Tools;
1549
1550[McpServerToolType]
1551public static class WeatherTools
1552{
1553 [McpServerTool, Description("Get weather alerts for a US state code.")]
1554 public static async Task<string> GetAlerts(
1555 HttpClient client,
1556 [Description("The US state code to get alerts for.")] string state)
1557 {
1558 using var jsonDocument = await client.ReadJsonDocumentAsync($"/alerts/active/area/{state}");
1559 var jsonElement = jsonDocument.RootElement;
1560 var alerts = jsonElement.GetProperty("features").EnumerateArray();
1561
1562 if (!alerts.Any())
1563 {
1564 return "No active alerts for this state.";
2981565 }
1566
1567 return string.Join("\n--\n", alerts.Select(alert =>
1568 {
1569 JsonElement properties = alert.GetProperty("properties");
1570 return $"""
1571 Event: {properties.GetProperty("event").GetString()}
1572 Area: {properties.GetProperty("areaDesc").GetString()}
1573 Severity: {properties.GetProperty("severity").GetString()}
1574 Description: {properties.GetProperty("description").GetString()}
1575 Instruction: {properties.GetProperty("instruction").GetString()}
1576 """;
1577 }));
1578 }
1579
1580 [McpServerTool, Description("Get weather forecast for a location.")]
1581 public static async Task<string> GetForecast(
1582 HttpClient client,
1583 [Description("Latitude of the location.")] double latitude,
1584 [Description("Longitude of the location.")] double longitude)
1585 {
1586 var pointUrl = string.Create(CultureInfo.InvariantCulture, $"/points/{latitude},{longitude}");
1587 using var jsonDocument = await client.ReadJsonDocumentAsync(pointUrl);
1588 var forecastUrl = jsonDocument.RootElement.GetProperty("properties").GetProperty("forecast").GetString()
1589 ?? throw new Exception($"No forecast URL provided by {client.BaseAddress}points/{latitude},{longitude}");
1590
1591 using var forecastDocument = await client.ReadJsonDocumentAsync(forecastUrl);
1592 var periods = forecastDocument.RootElement.GetProperty("properties").GetProperty("periods").EnumerateArray();
1593
1594 return string.Join("\n---\n", periods.Select(period => $"""
1595 {period.GetProperty("name").GetString()}
1596 Temperature: {period.GetProperty("temperature").GetInt32()}°F
1597 Wind: {period.GetProperty("windSpeed").GetString()} {period.GetProperty("windDirection").GetString()}
1598 Forecast: {period.GetProperty("detailedForecast").GetString()}
1599 """));
1600 }
1601}
1602```
1603
1604### Running the server
1605
1606Finally, run the server using the following command:
1607
1608```bash theme={null}
1609dotnet run
1610```
1611
1612This will start the server and listen for incoming requests on standard input/output.
1613
1614## Testing your server with Claude for Desktop
1615
1616> [!NOTE]
1617>
1618> Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
1619
1620First, make sure you have Claude for Desktop installed. [You can install the latest version
1621here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1622We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1623For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1624
1625```bash macOS/Linux theme={null}
1626code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1627```
1628
1629```powershell Windows theme={null}
1630code $env:AppData\Claude\claude_desktop_config.json
1631```
1632
1633You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1634In this case, we'll add our single weather server like so:
1635
1636```json macOS/Linux theme={null}
1637{
1638 "mcpServers": {
1639 "weather": {
1640 "command": "dotnet",
1641 "args": ["run", "--project", "/ABSOLUTE/PATH/TO/PROJECT", "--no-build"]
1642 }
1643 }
1644}
1645```
1646
1647```json Windows theme={null}
1648{
1649 "mcpServers": {
1650 "weather": {
1651 "command": "dotnet",
1652 "args": [
1653 "run",
1654 "--project",
1655 "C:\\ABSOLUTE\\PATH\\TO\\PROJECT",
1656 "--no-build"
1657 ]
1658 }
1659 }
1660}
1661```
1662
1663This tells Claude for Desktop:
1664
16651. There's an MCP server named "weather"
16662. Launch it by running `dotnet run /ABSOLUTE/PATH/TO/PROJECT`
1667 Save the file, and restart **Claude for Desktop**.
1668
1669**Ruby**
1670
1671Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby)
1672
1673### Prerequisite knowledge
1674
1675This quickstart assumes you have familiarity with:
1676
1677* Ruby
1678* LLMs like Claude
1679
1680### Logging in MCP Servers
1681
1682When implementing MCP servers, be careful about how you handle logging:
1683
1684**For STDIO-based servers:** Never use `puts` or `print`, as they write to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1685
1686**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1687
1688### Best Practices
1689
1690* Use a logging library that writes to stderr or files.
1691
1692### Quick Examples
1693
1694```ruby theme={null}
1695# ❌ Bad (STDIO)
1696puts "Processing request"
1697
1698# ✅ Good (STDIO)
1699require "logger"
1700logger = Logger.new($stderr)
1701logger.info("Processing request")
1702```
1703
1704### System requirements
1705
1706* Ruby 2.7 or higher installed.
1707
1708### Set up your environment
1709
1710First, let's make sure you have Ruby installed. You can check by running:
1711
1712```bash theme={null}
1713ruby --version
1714```
1715
1716Now, let's create and set up our project:
1717
1718```bash macOS/Linux theme={null}
1719# Create a new directory for our project
1720mkdir weather
1721cd weather
1722
1723# Create a Gemfile
1724bundle init
1725
1726# Add the MCP SDK dependency
1727bundle add mcp
1728
1729# Create our server file
1730touch weather.rb
1731```
1732
1733```powershell Windows theme={null}
1734# Create a new directory for our project
1735mkdir weather
1736cd weather
1737
1738# Create a Gemfile
1739bundle init
1740
1741# Add the MCP SDK dependency
1742bundle add mcp
1743
1744# Create our server file
1745new-item weather.rb
1746```
1747
1748Now let's dive into building your server.
1749
1750## Building your server
1751
1752### Importing packages and setting up constants
1753
1754Open `weather.rb` and add these requires and constants at the top:
1755
1756```ruby theme={null}
1757require "json"
1758require "mcp"
1759require "net/http"
1760require "uri"
1761
1762NWS_API_BASE = "https://api.weather.gov"
1763USER_AGENT = "weather-app/1.0"
1764```
1765
1766The `mcp` gem provides the Model Context Protocol SDK for Ruby, with classes for server implementation and stdio transport.
1767
1768### Helper methods
1769
1770Next, let's add helper methods for querying and formatting data from the National Weather Service API:
1771
1772```ruby theme={null}
1773module HelperMethods
1774 def make_nws_request(url)
1775 uri = URI(url)
1776 request = Net::HTTP::Get.new(uri)
1777 request["User-Agent"] = USER_AGENT
1778 request["Accept"] = "application/geo+json"
1779
1780 response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
1781 http.request(request)
1782 end
1783
1784 raise "HTTP #{response.code}: #{response.message}" unless response.is_a?(Net::HTTPSuccess)
1785
1786 JSON.parse(response.body)
1787 end
1788
1789 def format_alert(feature)
1790 properties = feature["properties"]
1791
1792 <<~ALERT
1793 Event: #{properties["event"] || "Unknown"}
1794 Area: #{properties["areaDesc"] || "Unknown"}
1795 Severity: #{properties["severity"] || "Unknown"}
1796 Description: #{properties["description"] || "No description available"}
1797 Instructions: #{properties["instruction"] || "No specific instructions provided"}
1798 ALERT
1799 end
1800end
1801```
1802
1803### Implementing tool execution
1804
1805Now let's define our tool classes. Each tool subclasses `MCP::Tool` and implements the tool logic:
1806
1807```ruby theme={null}
1808class GetAlerts < MCP::Tool
1809 extend HelperMethods
1810
1811 tool_name "get_alerts"
1812 description "Get weather alerts for a US state"
1813 input_schema(
1814 properties: {
1815 state: {
1816 type: "string",
1817 description: "Two-letter US state code (e.g. CA, NY)"
2991818 }
300 ```
301
302 ```json Windows theme={null}
303 {
304 "mcpServers": {
305 "weather": {
306 "command": "uv",
307 "args": [
308 "--directory",
309 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather",
310 "run",
311 "weather.py"
312 ]
313 }
1819 },
1820 required: ["state"]
1821 )
1822
1823 def self.call(state:)
1824 url = "#{NWS_API_BASE}/alerts/active/area/#{state.upcase}"
1825 data = make_nws_request(url)
1826
1827 if data["features"].empty?
1828 return MCP::Tool::Response.new([{
1829 type: "text",
1830 text: "No active alerts for this state."
1831 }])
1832 end
1833
1834 alerts = data["features"].map { |feature| format_alert(feature) }
1835 MCP::Tool::Response.new([{
1836 type: "text",
1837 text: alerts.join("\n---\n")
1838 }])
1839 end
1840end
1841
1842class GetForecast < MCP::Tool
1843 extend HelperMethods
1844
1845 tool_name "get_forecast"
1846 description "Get weather forecast for a location"
1847 input_schema(
1848 properties: {
1849 latitude: {
1850 type: "number",
1851 description: "Latitude of the location"
1852 },
1853 longitude: {
1854 type: "number",
1855 description: "Longitude of the location"
1856 }
1857 },
1858 required: ["latitude", "longitude"]
1859 )
1860
1861 def self.call(latitude:, longitude:)
1862 # First get the forecast grid endpoint.
1863 points_url = "#{NWS_API_BASE}/points/#{latitude},#{longitude}"
1864 points_data = make_nws_request(points_url)
1865
1866 # Get the forecast URL from the points response.
1867 forecast_url = points_data["properties"]["forecast"]
1868 forecast_data = make_nws_request(forecast_url)
1869
1870 # Format the periods into a readable forecast.
1871 periods = forecast_data["properties"]["periods"]
1872 forecasts = periods.first(5).map do |period|
1873 <<~FORECAST
1874 #{period["name"]}:
1875 Temperature: #{period["temperature"]}°#{period["temperatureUnit"]}
1876 Wind: #{period["windSpeed"]} #{period["windDirection"]}
1877 Forecast: #{period["detailedForecast"]}
1878 FORECAST
1879 end
1880
1881 MCP::Tool::Response.new([{
1882 type: "text",
1883 text: forecasts.join("\n---\n")
1884 }])
1885 end
1886end
1887```
1888
1889### Running the server
1890
1891Finally, initialize and run the server:
1892
1893```ruby theme={null}
1894server = MCP::Server.new(
1895 name: "weather",
1896 version: "1.0.0",
1897 tools: [GetAlerts, GetForecast]
1898)
1899
1900transport = MCP::Server::Transports::StdioTransport.new(server)
1901transport.open
1902```
1903
1904Your server is complete! Run `bundle exec ruby weather.rb` to start the MCP server, which will listen for messages from MCP hosts.
1905
1906Let's now test your server from an existing MCP host, Claude for Desktop.
1907
1908## Testing your server with Claude for Desktop
1909
1910> [!NOTE]
1911>
1912> Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
1913
1914First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1915
1916We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1917
1918For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1919
1920```bash macOS/Linux theme={null}
1921code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1922```
1923
1924```powershell Windows theme={null}
1925code $env:AppData\Claude\claude_desktop_config.json
1926```
1927
1928You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1929
1930In this case, we'll add our single weather server like so:
1931
1932```json macOS/Linux theme={null}
1933{
1934 "mcpServers": {
1935 "weather": {
1936 "command": "bundle",
1937 "args": ["exec", "ruby", "weather.rb"],
1938 "cwd": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather"
1939 }
1940 }
1941}
1942```
1943
1944```json Windows theme={null}
1945{
1946 "mcpServers": {
1947 "weather": {
1948 "command": "bundle",
1949 "args": ["exec", "ruby", "weather.rb"],
1950 "cwd": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather"
1951 }
1952 }
1953}
1954```
1955
1956> [!NOTE]
1957>
1958> Make sure you pass in the absolute path to your project directory in the `cwd` field. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
1959
1960This tells Claude for Desktop:
1961
19621. There's an MCP server named "weather"
19632. Launch it by running `bundle exec ruby weather.rb` in the specified directory
1964
1965Save the file, and restart **Claude for Desktop**.
1966
1967**Rust**
1968
1969Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust)
1970
1971### Prerequisite knowledge
1972
1973This quickstart assumes you have familiarity with:
1974
1975* Rust programming language
1976* Async/await in Rust
1977* LLMs like Claude
1978
1979### Logging in MCP Servers
1980
1981When implementing MCP servers, be careful about how you handle logging:
1982
1983**For STDIO-based servers:** Never use `println!()` or `print!()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
1984
1985**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1986
1987### Best Practices
1988
1989* Use a logging library that writes to stderr or files, such as `tracing` or `log` in Rust.
1990* Configure your logging framework to avoid stdout output.
1991
1992### Quick Examples
1993
1994```rust theme={null}
1995// ❌ Bad (STDIO)
1996println!("Processing request");
1997
1998// ✅ Good (STDIO)
1999eprintln!("Processing request"); // writes to stderr
2000```
2001
2002### System requirements
2003
2004* Rust 1.70 or higher installed.
2005* Cargo (comes with Rust installation).
2006
2007### Set up your environment
2008
2009First, let's install Rust if you haven't already. You can install Rust from [rust-lang.org](https://www.rust-lang.org/tools/install):
2010
2011```bash macOS/Linux theme={null}
2012curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
2013```
2014
2015```powershell Windows theme={null}
2016# Download and run rustup-init.exe from https://rustup.rs/
2017```
2018
2019Verify your Rust installation:
2020
2021```bash theme={null}
2022rustc --version
2023cargo --version
2024```
2025
2026Now, let's create and set up our project:
2027
2028```bash macOS/Linux theme={null}
2029# Create a new Rust project
2030cargo new weather
2031cd weather
2032```
2033
2034```powershell Windows theme={null}
2035# Create a new Rust project
2036cargo new weather
2037cd weather
2038```
2039
2040Update your `Cargo.toml` to add the required dependencies:
2041
2042```toml Cargo.toml theme={null}
2043[package]
2044name = "weather"
2045version = "0.1.0"
2046edition = "2024"
2047
2048[dependencies]
2049rmcp = { version = "0.3", features = ["server", "macros", "transport-io"] }
2050tokio = { version = "1.46", features = ["full"] }
2051reqwest = { version = "0.12", features = ["json"] }
2052serde = { version = "1.0", features = ["derive"] }
2053serde_json = "1.0"
2054anyhow = "1.0"
2055tracing = "0.1"
2056tracing-subscriber = { version = "0.3", features = ["env-filter", "std", "fmt"] }
2057```
2058
2059Now let's dive into building your server.
2060
2061## Building your server
2062
2063### Importing packages and constants
2064
2065Open `src/main.rs` and add these imports and constants at the top:
2066
2067```rust theme={null}
2068use anyhow::Result;
2069use rmcp::{
2070 ServerHandler, ServiceExt,
2071 handler::server::{router::tool::ToolRouter, tool::Parameters},
2072 model::*,
2073 schemars, tool, tool_handler, tool_router,
2074};
2075use serde::Deserialize;
2076use serde::de::DeserializeOwned;
2077
2078const NWS_API_BASE: &str = "https://api.weather.gov";
2079const USER_AGENT: &str = "weather-app/1.0";
2080```
2081
2082The `rmcp` crate provides the Model Context Protocol SDK for Rust, with features for server implementation, procedural macros, and stdio transport.
2083
2084### Data structures
2085
2086Next, let's define the data structures for deserializing responses from the National Weather Service API:
2087
2088```rust theme={null}
2089#[derive(Debug, Deserialize)]
2090struct AlertsResponse {
2091 features: Vec<AlertFeature>,
2092}
2093
2094#[derive(Debug, Deserialize)]
2095struct AlertFeature {
2096 properties: AlertProperties,
2097}
2098
2099#[derive(Debug, Deserialize)]
2100struct AlertProperties {
2101 event: Option<String>,
2102 #[serde(rename = "areaDesc")]
2103 area_desc: Option<String>,
2104 severity: Option<String>,
2105 description: Option<String>,
2106 instruction: Option<String>,
2107}
2108
2109#[derive(Debug, Deserialize)]
2110struct PointsResponse {
2111 properties: PointsProperties,
2112}
2113
2114#[derive(Debug, Deserialize)]
2115struct PointsProperties {
2116 forecast: String,
2117}
2118
2119#[derive(Debug, Deserialize)]
2120struct ForecastResponse {
2121 properties: ForecastProperties,
2122}
2123
2124#[derive(Debug, Deserialize)]
2125struct ForecastProperties {
2126 periods: Vec<ForecastPeriod>,
2127}
2128
2129#[derive(Debug, Deserialize)]
2130struct ForecastPeriod {
2131 name: String,
2132 temperature: i32,
2133 #[serde(rename = "temperatureUnit")]
2134 temperature_unit: String,
2135 #[serde(rename = "windSpeed")]
2136 wind_speed: String,
2137 #[serde(rename = "windDirection")]
2138 wind_direction: String,
2139 #[serde(rename = "detailedForecast")]
2140 detailed_forecast: String,
2141}
2142```
2143
2144Now define the request types that MCP clients will send:
2145
2146```rust theme={null}
2147#[derive(serde::Deserialize, schemars::JsonSchema)]
2148pub struct MCPForecastRequest {
2149 latitude: f32,
2150 longitude: f32,
2151}
2152
2153#[derive(serde::Deserialize, schemars::JsonSchema)]
2154pub struct MCPAlertRequest {
2155 state: String,
2156}
2157```
2158
2159### Helper functions
2160
2161Add helper functions for making API requests and formatting responses:
2162
2163```rust theme={null}
2164async fn make_nws_request<T: DeserializeOwned>(url: &str) -> Result<T> {
2165 let client = reqwest::Client::new();
2166 let rsp = client
2167 .get(url)
2168 .header(reqwest::header::USER_AGENT, USER_AGENT)
2169 .header(reqwest::header::ACCEPT, "application/geo+json")
2170 .send()
2171 .await?
2172 .error_for_status()?;
2173 Ok(rsp.json::<T>().await?)
2174}
2175
2176fn format_alert(feature: &AlertFeature) -> String {
2177 let props = &feature.properties;
2178 format!(
2179 "Event: {}\nArea: {}\nSeverity: {}\nDescription: {}\nInstructions: {}",
2180 props.event.as_deref().unwrap_or("Unknown"),
2181 props.area_desc.as_deref().unwrap_or("Unknown"),
2182 props.severity.as_deref().unwrap_or("Unknown"),
2183 props
2184 .description
2185 .as_deref()
2186 .unwrap_or("No description available"),
2187 props
2188 .instruction
2189 .as_deref()
2190 .unwrap_or("No specific instructions provided")
2191 )
2192}
2193
2194fn format_period(period: &ForecastPeriod) -> String {
2195 format!(
2196 "{}:\nTemperature: {}°{}\nWind: {} {}\nForecast: {}",
2197 period.name,
2198 period.temperature,
2199 period.temperature_unit,
2200 period.wind_speed,
2201 period.wind_direction,
2202 period.detailed_forecast
2203 )
2204}
2205```
2206
2207### Implementing the Weather server and tools
2208
2209Now let's implement the main Weather server struct with the tool handlers:
2210
2211```rust theme={null}
2212pub struct Weather {
2213 tool_router: ToolRouter<Weather>,
2214}
2215
2216#[tool_router]
2217impl Weather {
2218 fn new() -> Self {
2219 Self {
2220 tool_router: Self::tool_router(),
3142221 }
315 }
316 ```
317 </CodeGroup>
318
319 <Warning>
320 You may need to put the full path to the `uv` executable in the `command` field. You can get this by running `which uv` on macOS/Linux or `where uv` on Windows.
321 </Warning>
322
323 <Note>
324 Make sure you pass in the absolute path to your server. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
325 </Note>
326
327 This tells Claude for Desktop:
328
329 1. There's an MCP server named "weather"
330 2. To launch it by running `uv --directory /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather run weather.py`
331
332 Save the file, and restart **Claude for Desktop**.
333 </Tab>
334
335 <Tab title="TypeScript">
336 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript)
337
338 ### Prerequisite knowledge
339
340 This quickstart assumes you have familiarity with:
341
342 * TypeScript
343 * LLMs like Claude
344
345 ### Logging in MCP Servers
346
347 When implementing MCP servers, be careful about how you handle logging:
348
349 **For STDIO-based servers:** Never use `console.log()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
350
351 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
352
353 ### Best Practices
354
355 * Use `console.error()` which writes to stderr, or use a logging library that writes to stderr or files.
356
357 ### Quick Examples
358
359 ```javascript theme={null}
360 // ❌ Bad (STDIO)
361 console.log("Server started");
362
363 // ✅ Good (STDIO)
364 console.error("Server started"); // stderr is safe
365 ```
366
367 ### System requirements
368
369 For TypeScript, make sure you have the latest version of Node installed.
370
371 ### Set up your environment
372
373 First, let's install Node.js and npm if you haven't already. You can download them from [nodejs.org](https://nodejs.org/).
374 Verify your Node.js installation:
375
376 ```bash theme={null}
377 node --version
378 npm --version
379 ```
380
381 For this tutorial, you'll need Node.js version 16 or higher.
382
383 Now, let's create and set up our project:
384
385 <CodeGroup>
386 ```bash macOS/Linux theme={null}
387 # Create a new directory for our project
388 mkdir weather
389 cd weather
390
391 # Initialize a new npm project
392 npm init -y
393
394 # Install dependencies
395 npm install @modelcontextprotocol/sdk zod@3
396 npm install -D @types/node typescript
397
398 # Create our files
399 mkdir src
400 touch src/index.ts
401 ```
402
403 ```powershell Windows theme={null}
404 # Create a new directory for our project
405 md weather
406 cd weather
407
408 # Initialize a new npm project
409 npm init -y
410
411 # Install dependencies
412 npm install @modelcontextprotocol/sdk zod@3
413 npm install -D @types/node typescript
414
415 # Create our files
416 md src
417 new-item src\index.ts
418 ```
419 </CodeGroup>
420
421 Update your package.json to add type: "module" and a build script:
422
423 ```json package.json theme={null}
424 {
425 "type": "module",
426 "bin": {
427 "weather": "./build/index.js"
428 },
429 "scripts": {
430 "build": "tsc && chmod 755 build/index.js"
431 },
432 "files": ["build"]
433 }
434 ```
435
436 Create a `tsconfig.json` in the root of your project:
437
438 ```json tsconfig.json theme={null}
439 {
440 "compilerOptions": {
441 "target": "ES2022",
442 "module": "Node16",
443 "moduleResolution": "Node16",
444 "outDir": "./build",
445 "rootDir": "./src",
446 "strict": true,
447 "esModuleInterop": true,
448 "skipLibCheck": true,
449 "forceConsistentCasingInFileNames": true
450 },
451 "include": ["src/**/*"],
452 "exclude": ["node_modules"]
453 }
454 ```
455
456 Now let's dive into building your server.
457
458 ## Building your server
459
460 ### Importing packages and setting up the instance
461
462 Add these to the top of your `src/index.ts`:
463
464 ```typescript theme={null}
465 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
466 import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
467 import { z } from "zod";
468
469 const NWS_API_BASE = "https://api.weather.gov";
470 const USER_AGENT = "weather-app/1.0";
471
472 // Create server instance
473 const server = new McpServer({
474 name: "weather",
475 version: "1.0.0",
476 });
477 ```
478
479 ### Helper functions
480
481 Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
482
483 ```typescript theme={null}
484 // Helper function for making NWS API requests
485 async function makeNWSRequest<T>(url: string): Promise<T | null> {
486 const headers = {
487 "User-Agent": USER_AGENT,
488 Accept: "application/geo+json",
489 };
490
491 try {
492 const response = await fetch(url, { headers });
493 if (!response.ok) {
494 throw new Error(`HTTP error! status: ${response.status}`);
2222 }
2223
2224 #[tool(description = "Get weather alerts for a US state.")]
2225 async fn get_alerts(
2226 &self,
2227 Parameters(MCPAlertRequest { state }): Parameters<MCPAlertRequest>,
2228 ) -> String {
2229 let url = format!(
2230 "{}/alerts/active/area/{}",
2231 NWS_API_BASE,
2232 state.to_uppercase()
2233 );
2234
2235 match make_nws_request::<AlertsResponse>(&url).await {
2236 Ok(data) => {
2237 if data.features.is_empty() {
2238 "No active alerts for this state.".to_string()
2239 } else {
2240 data.features
2241 .iter()
2242 .map(format_alert)
2243 .collect::<Vec<_>>()
2244 .join("\n---\n")
2245 }
2246 }
2247 Err(_) => "Unable to fetch alerts or no alerts found.".to_string(),
4952248 }
496 return (await response.json()) as T;
497 } catch (error) {
498 console.error("Error making NWS request:", error);
499 return null;
500 }
501 }
502
503 interface AlertFeature {
504 properties: {
505 event?: string;
506 areaDesc?: string;
507 severity?: string;
508 status?: string;
509 headline?: string;
510 };
511 }
512
513 // Format alert data
514 function formatAlert(feature: AlertFeature): string {
515 const props = feature.properties;
516 return [
517 `Event: ${props.event || "Unknown"}`,
518 `Area: ${props.areaDesc || "Unknown"}`,
519 `Severity: ${props.severity || "Unknown"}`,
520 `Status: ${props.status || "Unknown"}`,
521 `Headline: ${props.headline || "No headline"}`,
522 "---",
523 ].join("\n");
524 }
525
526 interface ForecastPeriod {
527 name?: string;
528 temperature?: number;
529 temperatureUnit?: string;
530 windSpeed?: string;
531 windDirection?: string;
532 shortForecast?: string;
533 }
534
535 interface AlertsResponse {
536 features: AlertFeature[];
537 }
538
539 interface PointsResponse {
540 properties: {
541 forecast?: string;
542 };
543 }
544
545 interface ForecastResponse {
546 properties: {
547 periods: ForecastPeriod[];
548 };
549 }
550 ```
551
552 ### Implementing tool execution
553
554 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
555
556 ```typescript theme={null}
557 // Register weather tools
558
559 server.registerTool(
560 "get_alerts",
561 {
562 description: "Get weather alerts for a state",
563 inputSchema: {
564 state: z
565 .string()
566 .length(2)
567 .describe("Two-letter state code (e.g. CA, NY)"),
568 },
569 },
570 async ({ state }) => {
571 const stateCode = state.toUpperCase();
572 const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`;
573 const alertsData = await makeNWSRequest<AlertsResponse>(alertsUrl);
574
575 if (!alertsData) {
576 return {
577 content: [
578 {
579 type: "text",
580 text: "Failed to retrieve alerts data",
581 },
582 ],
583 };
2249 }
2250
2251 #[tool(description = "Get weather forecast for a location.")]
2252 async fn get_forecast(
2253 &self,
2254 Parameters(MCPForecastRequest {
2255 latitude,
2256 longitude,
2257 }): Parameters<MCPForecastRequest>,
2258 ) -> String {
2259 let points_url = format!("{NWS_API_BASE}/points/{latitude},{longitude}");
2260 let Ok(points_data) = make_nws_request::<PointsResponse>(&points_url).await else {
2261 return "Unable to fetch forecast data for this location.".to_string();
2262 };
2263
2264 let forecast_url = points_data.properties.forecast;
2265
2266 let Ok(forecast_data) = make_nws_request::<ForecastResponse>(&forecast_url).await else {
2267 return "Unable to fetch forecast data for this location.".to_string();
2268 };
2269
2270 let periods = &forecast_data.properties.periods;
2271 let forecast_summary: String = periods
2272 .iter()
2273 .take(5) // Next 5 periods only
2274 .map(format_period)
2275 .collect::<Vec<String>>()
2276 .join("\n---\n");
2277 forecast_summary
2278 }
2279}
2280```
2281
2282The `#[tool_router]` macro automatically generates the routing logic, and the `#[tool]` attribute marks methods as MCP tools.
2283
2284### Implementing the ServerHandler
2285
2286Implement the `ServerHandler` trait to define server capabilities:
2287
2288```rust theme={null}
2289#[tool_handler]
2290impl ServerHandler for Weather {
2291 fn get_info(&self) -> ServerInfo {
2292 ServerInfo {
2293 capabilities: ServerCapabilities::builder().enable_tools().build(),
2294 ..Default::default()
5842295 }
585
586 const features = alertsData.features || [];
587 if (!features.length) {
588 return {
589 content: [
590 {
591 type: "text",
592 text: `No active alerts for ${stateCode}`,
593 },
594 ],
595 };
596 }
597
598 const formattedAlerts = features.map(formatAlert);
599 const alertsText = `Active alerts for ${stateCode}:\n\n${formattedAlerts.join("\n")}`;
600
601 return {
602 content: [
603 {
604 type: "text",
605 text: alertsText,
606 },
607 ],
608 };
609 },
610 );
611
612 server.registerTool(
613 "get_forecast",
614 {
615 description: "Get weather forecast for a location",
616 inputSchema: {
617 latitude: z
618 .number()
619 .min(-90)
620 .max(90)
621 .describe("Latitude of the location"),
622 longitude: z
623 .number()
624 .min(-180)
625 .max(180)
626 .describe("Longitude of the location"),
627 },
628 },
629 async ({ latitude, longitude }) => {
630 // Get grid point data
631 const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`;
632 const pointsData = await makeNWSRequest<PointsResponse>(pointsUrl);
633
634 if (!pointsData) {
635 return {
636 content: [
637 {
638 type: "text",
639 text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`,
640 },
641 ],
642 };
643 }
644
645 const forecastUrl = pointsData.properties?.forecast;
646 if (!forecastUrl) {
647 return {
648 content: [
649 {
650 type: "text",
651 text: "Failed to get forecast URL from grid point data",
652 },
653 ],
654 };
655 }
656
657 // Get forecast data
658 const forecastData = await makeNWSRequest<ForecastResponse>(forecastUrl);
659 if (!forecastData) {
660 return {
661 content: [
662 {
663 type: "text",
664 text: "Failed to retrieve forecast data",
665 },
666 ],
667 };
668 }
669
670 const periods = forecastData.properties?.periods || [];
671 if (periods.length === 0) {
672 return {
673 content: [
674 {
675 type: "text",
676 text: "No forecast periods available",
677 },
678 ],
679 };
680 }
681
682 // Format forecast periods
683 const formattedForecast = periods.map((period: ForecastPeriod) =>
684 [
685 `${period.name || "Unknown"}:`,
686 `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
687 `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
688 `${period.shortForecast || "No forecast available"}`,
689 "---",
690 ].join("\n"),
691 );
692
693 const forecastText = `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join("\n")}`;
694
695 return {
696 content: [
697 {
698 type: "text",
699 text: forecastText,
700 },
701 ],
702 };
703 },
704 );
705 ```
706
707 ### Running the server
708
709 Finally, implement the main function to run the server:
710
711 ```typescript theme={null}
712 async function main() {
713 const transport = new StdioServerTransport();
714 await server.connect(transport);
715 console.error("Weather MCP Server running on stdio");
716 }
717
718 main().catch((error) => {
719 console.error("Fatal error in main():", error);
720 process.exit(1);
721 });
722 ```
723
724 Make sure to run `npm run build` to build your server! This is a very important step in getting your server to connect.
725
726 Let's now test your server from an existing MCP host, Claude for Desktop.
727
728 ## Testing your server with Claude for Desktop
729
730 <Note>
731 Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
732 </Note>
733
734 First, make sure you have Claude for Desktop installed. [You can install the latest version
735 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
736
737 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
738
739 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
740
741 <CodeGroup>
742 ```bash macOS/Linux theme={null}
743 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
744 ```
745
746 ```powershell Windows theme={null}
747 code $env:AppData\Claude\claude_desktop_config.json
748 ```
749 </CodeGroup>
750
751 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
752
753 In this case, we'll add our single weather server like so:
754
755 <CodeGroup>
756 ```json macOS/Linux theme={null}
757 {
758 "mcpServers": {
759 "weather": {
760 "command": "node",
761 "args": ["/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js"]
762 }
763 }
764 }
765 ```
766
767 ```json Windows theme={null}
768 {
769 "mcpServers": {
770 "weather": {
771 "command": "node",
772 "args": ["C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\index.js"]
773 }
774 }
775 }
776 ```
777 </CodeGroup>
778
779 This tells Claude for Desktop:
780
781 1. There's an MCP server named "weather"
782 2. Launch it by running `node /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js`
783
784 Save the file, and restart **Claude for Desktop**.
785 </Tab>
786
787 <Tab title="Java">
788 <Note>
789 This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
790 To learn how to create sync and async MCP Servers, manually, consult the [Java SDK Server](https://java.sdk.modelcontextprotocol.io/) documentation.
791 </Note>
792
793 Let's get started with building our weather server!
794 [You can find the complete code for what we'll be building here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-stdio-server)
795
796 For more information, see the [MCP Server Boot Starter](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html) reference documentation.
797 For manual MCP Server implementation, refer to the [MCP Server Java SDK documentation](https://java.sdk.modelcontextprotocol.io/).
798
799 ### Logging in MCP Servers
800
801 When implementing MCP servers, be careful about how you handle logging:
802
803 **For STDIO-based servers:** Never use `System.out.println()` or `System.out.print()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
804
805 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
806
807 ### Best Practices
808
809 * Use a logging library that writes to stderr or files.
810 * Ensure any configured logging library will not write to stdout.
811
812 ### System requirements
813
814 * Java 17 or higher installed.
815 * [Spring Boot 3.3.x](https://docs.spring.io/spring-boot/installing.html) or higher
816
817 ### Set up your environment
818
819 Use the [Spring Initializer](https://start.spring.io/) to bootstrap the project.
820
821 You will need to add the following dependencies:
822
823 <CodeGroup>
824 ```xml Maven theme={null}
825 <dependencies>
826 <dependency>
827 <groupId>org.springframework.ai</groupId>
828 <artifactId>spring-ai-starter-mcp-server</artifactId>
829 </dependency>
830
831 <dependency>
832 <groupId>org.springframework</groupId>
833 <artifactId>spring-web</artifactId>
834 </dependency>
835 </dependencies>
836 ```
837
838 ```groovy Gradle theme={null}
839 dependencies {
840 implementation platform("org.springframework.ai:spring-ai-starter-mcp-server")
841 implementation platform("org.springframework:spring-web")
842 }
843 ```
844 </CodeGroup>
845
846 Then configure your application by setting the application properties:
847
848 <CodeGroup>
849 ```bash application.properties theme={null}
850 spring.main.bannerMode=off
851 logging.pattern.console=
852 ```
853
854 ```yaml application.yml theme={null}
855 logging:
856 pattern:
857 console:
858 spring:
859 main:
860 banner-mode: off
861 ```
862 </CodeGroup>
863
864 The [Server Configuration Properties](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html#_configuration_properties) documents all available properties.
865
866 Now let's dive into building your server.
867
868 ## Building your server
869
870 ### Weather Service
871
872 Let's implement a [WeatherService.java](https://github.com/spring-projects/spring-ai-examples/blob/main/model-context-protocol/weather/starter-stdio-server/src/main/java/org/springframework/ai/mcp/sample/server/WeatherService.java) that uses a REST client to query the data from the National Weather Service API:
873
874 ```java theme={null}
875 @Service
876 public class WeatherService {
877
878 private final RestClient restClient;
879
880 public WeatherService() {
881 this.restClient = RestClient.builder()
882 .baseUrl("https://api.weather.gov")
883 .defaultHeader("Accept", "application/geo+json")
884 .defaultHeader("User-Agent", "WeatherApiClient/1.0 ([email protected])")
885 .build();
886 }
887
888 @Tool(description = "Get weather forecast for a specific latitude/longitude")
889 public String getWeatherForecastByLocation(
890 double latitude, // Latitude coordinate
891 double longitude // Longitude coordinate
892 ) {
893 // Returns detailed forecast including:
894 // - Temperature and unit
895 // - Wind speed and direction
896 // - Detailed forecast description
897 }
898
899 @Tool(description = "Get weather alerts for a US state")
900 public String getAlerts(
901 @ToolParam(description = "Two-letter US state code (e.g. CA, NY)") String state
902 ) {
903 // Returns active alerts including:
904 // - Event type
905 // - Affected area
906 // - Severity
907 // - Description
908 // - Safety instructions
909 }
910
911 // ......
912 }
913 ```
914
915 The `@Service` annotation will auto-register the service in your application context.
916 The Spring AI `@Tool` annotation makes it easy to create and maintain MCP tools.
917
918 The auto-configuration will automatically register these tools with the MCP server.
919
920 ### Create your Boot Application
921
922 ```java theme={null}
923 @SpringBootApplication
924 public class McpServerApplication {
925
926 public static void main(String[] args) {
927 SpringApplication.run(McpServerApplication.class, args);
928 }
929
930 @Bean
931 public ToolCallbackProvider weatherTools(WeatherService weatherService) {
932 return MethodToolCallbackProvider.builder().toolObjects(weatherService).build();
933 }
934 }
935 ```
936
937 Uses the `MethodToolCallbackProvider` utils to convert the `@Tools` into actionable callbacks used by the MCP server.
938
939 ### Running the server
940
941 Finally, let's build the server:
942
943 ```bash theme={null}
944 ./mvnw clean install
945 ```
946
947 This will generate an `mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar` file within the `target` folder.
948
949 Let's now test your server from an existing MCP host, Claude for Desktop.
950
951 ## Testing your server with Claude for Desktop
952
953 <Note>
954 Claude for Desktop is not yet available on Linux.
955 </Note>
956
957 First, make sure you have Claude for Desktop installed.
958 [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
959
960 We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
961 To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
962 Make sure to create the file if it doesn't exist.
963
964 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
965
966 <CodeGroup>
967 ```bash macOS/Linux theme={null}
968 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
969 ```
970
971 ```powershell Windows theme={null}
972 code $env:AppData\Claude\claude_desktop_config.json
973 ```
974 </CodeGroup>
975
976 You'll then add your servers in the `mcpServers` key.
977 The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
978
979 In this case, we'll add our single weather server like so:
980
981 <CodeGroup>
982 ```json macOS/Linux theme={null}
983 {
984 "mcpServers": {
985 "spring-ai-mcp-weather": {
986 "command": "java",
987 "args": [
988 "-Dspring.ai.mcp.server.stdio=true",
989 "-jar",
990 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
991 ]
992 }
993 }
994 }
995 ```
996
997 ```json Windows theme={null}
998 {
999 "mcpServers": {
1000 "spring-ai-mcp-weather": {
1001 "command": "java",
1002 "args": [
1003 "-Dspring.ai.mcp.server.transport=STDIO",
1004 "-jar",
1005 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
1006 ]
1007 }
1008 }
1009 }
1010 ```
1011 </CodeGroup>
1012
1013 <Note>
1014 Make sure you pass in the absolute path to your server.
1015 </Note>
1016
1017 This tells Claude for Desktop:
1018
1019 1. There's an MCP server named "my-weather-server"
1020 2. To launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar`
1021
1022 Save the file, and restart **Claude for Desktop**.
1023
1024 ## Testing your server with Java client
1025
1026 ### Create an MCP Client manually
1027
1028 Use the `McpClient` to connect to the server:
1029
1030 ```java theme={null}
1031 var stdioParams = ServerParameters.builder("java")
1032 .args("-jar", "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar")
1033 .build();
1034
1035 var stdioTransport = new StdioClientTransport(stdioParams);
1036
1037 var mcpClient = McpClient.sync(stdioTransport).build();
1038
1039 mcpClient.initialize();
1040
1041 ListToolsResult toolsList = mcpClient.listTools();
1042
1043 CallToolResult weather = mcpClient.callTool(
1044 new CallToolRequest("getWeatherForecastByLocation",
1045 Map.of("latitude", "47.6062", "longitude", "-122.3321")));
1046
1047 CallToolResult alert = mcpClient.callTool(
1048 new CallToolRequest("getAlerts", Map.of("state", "NY")));
1049
1050 mcpClient.closeGracefully();
1051 ```
1052
1053 ### Use MCP Client Boot Starter
1054
1055 Create a new boot starter application using the `spring-ai-starter-mcp-client` dependency:
1056
1057 ```xml theme={null}
1058 <dependency>
1059 <groupId>org.springframework.ai</groupId>
1060 <artifactId>spring-ai-starter-mcp-client</artifactId>
1061 </dependency>
1062 ```
1063
1064 and set the `spring.ai.mcp.client.stdio.servers-configuration` property to point to your `claude_desktop_config.json`.
1065 You can reuse the existing Anthropic Desktop configuration:
1066
1067 ```properties theme={null}
1068 spring.ai.mcp.client.stdio.servers-configuration=file:PATH/TO/claude_desktop_config.json
1069 ```
1070
1071 When you start your client application, the auto-configuration will automatically create MCP clients from the claude\_desktop\_config.json.
1072
1073 For more information, see the [MCP Client Boot Starters](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-client-boot-starter-docs.html) reference documentation.
1074
1075 ## More Java MCP Server examples
1076
1077 The [starter-webflux-server](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-webflux-server) demonstrates how to create an MCP server using SSE transport.
1078 It showcases how to define and register MCP Tools, Resources, and Prompts, using the Spring Boot's auto-configuration capabilities.
1079 </Tab>
1080
1081 <Tab title="Kotlin">
1082 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/weather-stdio-server)
1083
1084 ### Prerequisite knowledge
1085
1086 This quickstart assumes you have familiarity with:
1087
1088 * Kotlin
1089 * LLMs like Claude
1090
1091 ### Logging in MCP Servers
1092
1093 When implementing MCP servers, be careful about how you handle logging:
1094
1095 **For STDIO-based servers:** Never use `println()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1096
1097 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1098
1099 ### Best Practices
1100
1101 * Use a logging library that writes to stderr or files.
1102
1103 ### System requirements
1104
1105 * JDK 11 or higher installed.
1106
1107 ### Set up your environment
1108
1109 First, let's install `java` and `gradle` if you haven't already.
1110 You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1111 Verify your `java` installation:
1112
1113 ```bash theme={null}
1114 java --version
1115 ```
1116
1117 Now, let's create and set up your project:
1118
1119 <CodeGroup>
1120 ```bash macOS/Linux theme={null}
1121 # Create a new directory for our project
1122 mkdir weather
1123 cd weather
1124
1125 # Initialize a new kotlin project
1126 gradle init
1127 ```
1128
1129 ```powershell Windows theme={null}
1130 # Create a new directory for our project
1131 md weather
1132 cd weather
1133
1134 # Initialize a new kotlin project
1135 gradle init
1136 ```
1137 </CodeGroup>
1138
1139 After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1140
1141 Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1142
1143 After creating the project, replace the contents of your `build.gradle.kts` with:
1144
1145 ```kotlin build.gradle.kts theme={null}
1146 // Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1147 val mcpVersion = "0.9.0"
1148 val ktorVersion = "3.2.3"
1149 val slf4jVersion = "2.0.17"
1150
1151 plugins {
1152 kotlin("jvm") version "2.3.20"
1153 kotlin("plugin.serialization") version "2.3.20"
1154 id("com.gradleup.shadow") version "8.3.9"
1155 application
1156 }
1157
1158 application {
1159 mainClass.set("MainKt")
1160 }
1161
1162 dependencies {
1163 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1164 implementation("io.ktor:ktor-client-content-negotiation:$ktorVersion")
1165 implementation("io.ktor:ktor-serialization-kotlinx-json:$ktorVersion")
1166 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1167 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1168 }
1169 ```
1170
1171 Verify that everything is set up correctly:
1172
1173 ```bash theme={null}
1174 ./gradlew build
1175 ```
1176
1177 Now let's dive into building your server.
1178
1179 ## Building your server
1180
1181 ### Setting up the instance
1182
1183 Add a server initialization function:
1184
1185 ```kotlin theme={null}
1186 fun runMcpServer() {
1187 val server = Server(
1188 Implementation(
1189 name = "weather",
1190 version = "1.0.0",
1191 ),
1192 ServerOptions(
1193 capabilities = ServerCapabilities(tools = ServerCapabilities.Tools(listChanged = true)),
1194 ),
1195 )
1196
1197 // register tools on server here
1198
1199 val transport = StdioServerTransport(
1200 System.`in`.asInput(),
1201 System.out.asSink().buffered(),
1202 )
1203
1204 runBlocking {
1205 val session = server.createSession(transport)
1206 val done = Job()
1207 session.onClose {
1208 done.complete()
1209 }
1210 done.join()
1211 }
1212 }
1213 ```
1214
1215 ### Weather API helper functions
1216
1217 Next, let's add functions and data classes for querying and converting responses from the National Weather Service API:
1218
1219 ```kotlin theme={null}
1220 val httpClient = HttpClient(CIO) {
1221 defaultRequest {
1222 url("https://api.weather.gov")
1223 headers {
1224 append("Accept", "application/geo+json")
1225 append("User-Agent", "WeatherApiClient/1.0")
1226 }
1227 contentType(ContentType.Application.Json)
1228 }
1229 install(ContentNegotiation) {
1230 json(Json { ignoreUnknownKeys = true })
1231 }
1232 }
1233
1234 // Extension function to fetch weather alerts for a given state
1235 suspend fun HttpClient.getAlerts(state: String): List<String> {
1236 val alerts = this.get("/alerts/active/area/$state").body<AlertsResponse>()
1237 return alerts.features.map { feature ->
1238 """
1239 Event: ${feature.properties.event}
1240 Area: ${feature.properties.areaDesc}
1241 Severity: ${feature.properties.severity}
1242 Status: ${feature.properties.status}
1243 Headline: ${feature.properties.headline}
1244 """.trimIndent()
1245 }
1246 }
1247
1248 // Extension function to fetch forecast information for given latitude and longitude
1249 suspend fun HttpClient.getForecast(latitude: Double, longitude: Double): List<String> {
1250 val points = this.get("/points/$latitude,$longitude").body<PointsResponse>()
1251 val forecastUrl = points.properties.forecast ?: error("No forecast URL available")
1252 val forecast = this.get(forecastUrl).body<ForecastResponse>()
1253 return forecast.properties.periods.map { period ->
1254 """
1255 ${period.name}:
1256 Temperature: ${period.temperature}°${period.temperatureUnit}
1257 Wind: ${period.windSpeed} ${period.windDirection}
1258 ${period.shortForecast}
1259 """.trimIndent()
1260 }
1261 }
1262
1263 @Serializable
1264 data class PointsResponse(val properties: PointsProperties)
1265
1266 @Serializable
1267 data class PointsProperties(val forecast: String? = null)
1268
1269 @Serializable
1270 data class ForecastResponse(val properties: ForecastProperties)
1271
1272 @Serializable
1273 data class ForecastProperties(val periods: List<ForecastPeriod> = emptyList())
1274
1275 @Serializable
1276 data class ForecastPeriod(
1277 val name: String? = null,
1278 val temperature: Int? = null,
1279 val temperatureUnit: String? = null,
1280 val windSpeed: String? = null,
1281 val windDirection: String? = null,
1282 val shortForecast: String? = null,
1283 )
1284
1285 @Serializable
1286 data class AlertsResponse(val features: List<AlertFeature> = emptyList())
1287
1288 @Serializable
1289 data class AlertFeature(val properties: AlertProperties)
1290
1291 @Serializable
1292 data class AlertProperties(
1293 val event: String? = null,
1294 val areaDesc: String? = null,
1295 val severity: String? = null,
1296 val status: String? = null,
1297 val headline: String? = null,
1298 )
1299 ```
1300
1301 ### Implementing tool execution
1302
1303 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
1304
1305 ```kotlin theme={null}
1306 // Register weather tools
1307
1308 server.addTool(
1309 name = "get_alerts",
1310 description = "Get weather alerts for a US state. Input is a two-letter US state code (e.g. CA, NY)",
1311 inputSchema = ToolSchema(
1312 properties = buildJsonObject {
1313 putJsonObject("state") {
1314 put("type", "string")
1315 put("description", "Two-letter US state code (e.g. CA, NY)")
1316 }
1317 },
1318 required = listOf("state"),
1319 ),
1320 ) { request ->
1321 val state = request.arguments?.get("state")?.jsonPrimitive?.content
1322 ?: return@addTool CallToolResult(
1323 content = listOf(TextContent("The 'state' parameter is required.")),
1324 )
1325
1326 val alerts = httpClient.getAlerts(state)
1327 CallToolResult(content = alerts.map { TextContent(it) })
1328 }
1329
1330 server.addTool(
1331 name = "get_forecast",
1332 description = "Get weather forecast for a location. Note: only US locations are supported by the NWS API.",
1333 inputSchema = ToolSchema(
1334 properties = buildJsonObject {
1335 putJsonObject("latitude") {
1336 put("type", "number")
1337 put("description", "Latitude of the location")
1338 }
1339 putJsonObject("longitude") {
1340 put("type", "number")
1341 put("description", "Longitude of the location")
1342 }
1343 },
1344 required = listOf("latitude", "longitude"),
1345 ),
1346 ) { request ->
1347 val latitude = request.arguments?.get("latitude")?.jsonPrimitive?.doubleOrNull
1348 val longitude = request.arguments?.get("longitude")?.jsonPrimitive?.doubleOrNull
1349 if (latitude == null || longitude == null) {
1350 return@addTool CallToolResult(
1351 content = listOf(TextContent("The 'latitude' and 'longitude' parameters are required.")),
1352 )
1353 }
1354
1355 val forecast = httpClient.getForecast(latitude, longitude)
1356 CallToolResult(content = forecast.map { TextContent(it) })
1357 }
1358 ```
1359
1360 ### Running the server
1361
1362 Finally, implement the main function to run the server:
1363
1364 ```kotlin theme={null}
1365 fun main() = runMcpServer()
1366 ```
1367
1368 You can run the server directly during development:
1369
1370 ```bash theme={null}
1371 ./gradlew run
1372 ```
1373
1374 For production use, build the shadow JAR:
1375
1376 ```bash theme={null}
1377 ./gradlew build
1378 java -jar build/libs/weather-0.1.0-all.jar
1379 ```
1380
1381 Let's now test your server from an existing MCP host, Claude for Desktop.
1382
1383 ## Testing your server with Claude for Desktop
1384
1385 <Note>
1386 Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
1387 </Note>
1388
1389 First, make sure you have Claude for Desktop installed. [You can install the latest version
1390 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1391
1392 We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
1393 To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
1394 Make sure to create the file if it doesn't exist.
1395
1396 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1397
1398 <CodeGroup>
1399 ```bash macOS/Linux theme={null}
1400 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1401 ```
1402
1403 ```powershell Windows theme={null}
1404 code $env:AppData\Claude\claude_desktop_config.json
1405 ```
1406 </CodeGroup>
1407
1408 You'll then add your servers in the `mcpServers` key.
1409 The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1410
1411 In this case, we'll add our single weather server like so:
1412
1413 <CodeGroup>
1414 ```json macOS/Linux theme={null}
1415 {
1416 "mcpServers": {
1417 "weather": {
1418 "command": "java",
1419 "args": [
1420 "-jar",
1421 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar"
1422 ]
1423 }
1424 }
1425 }
1426 ```
1427
1428 ```json Windows theme={null}
1429 {
1430 "mcpServers": {
1431 "weather": {
1432 "command": "java",
1433 "args": [
1434 "-jar",
1435 "C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\libs\\weather-0.1.0-all.jar"
1436 ]
1437 }
1438 }
1439 }
1440 ```
1441 </CodeGroup>
1442
1443 This tells Claude for Desktop:
1444
1445 1. There's an MCP server named "weather"
1446 2. Launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar`
1447
1448 Save the file, and restart **Claude for Desktop**.
1449 </Tab>
1450
1451 <Tab title="C#">
1452 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartWeatherServer)
1453
1454 ### Prerequisite knowledge
1455
1456 This quickstart assumes you have familiarity with:
1457
1458 * C#
1459 * LLMs like Claude
1460 * .NET 8 or higher
1461
1462 ### Logging in MCP Servers
1463
1464 When implementing MCP servers, be careful about how you handle logging:
1465
1466 **For STDIO-based servers:** Never use `Console.WriteLine()` or `Console.Write()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
1467
1468 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1469
1470 ### Best Practices
1471
1472 * Use a logging library that writes to stderr or files.
1473
1474 ### System requirements
1475
1476 * [.NET 8 SDK](https://dotnet.microsoft.com/download/dotnet/8.0) or higher installed.
1477
1478 ### Set up your environment
1479
1480 First, let's install `dotnet` if you haven't already. You can download `dotnet` from [official Microsoft .NET website](https://dotnet.microsoft.com/download/). Verify your `dotnet` installation:
1481
1482 ```bash theme={null}
1483 dotnet --version
1484 ```
1485
1486 Now, let's create and set up your project:
1487
1488 <CodeGroup>
1489 ```bash macOS/Linux theme={null}
1490 # Create a new directory for our project
1491 mkdir weather
1492 cd weather
1493 # Initialize a new C# project
1494 dotnet new console
1495 ```
1496
1497 ```powershell Windows theme={null}
1498 # Create a new directory for our project
1499 mkdir weather
1500 cd weather
1501 # Initialize a new C# project
1502 dotnet new console
1503 ```
1504 </CodeGroup>
1505
1506 After running `dotnet new console`, you will be presented with a new C# project.
1507 You can open the project in your favorite IDE, such as [Visual Studio](https://visualstudio.microsoft.com/) or [Rider](https://www.jetbrains.com/rider/).
1508 Alternatively, you can create a C# application using the [Visual Studio project wizard](https://learn.microsoft.com/en-us/visualstudio/get-started/csharp/tutorial-console?view=vs-2022).
1509 After creating the project, add NuGet package for the Model Context Protocol SDK and hosting:
1510
1511 ```bash theme={null}
1512 # Add the Model Context Protocol SDK NuGet package
1513 dotnet add package ModelContextProtocol --prerelease
1514 # Add the .NET Hosting NuGet package
1515 dotnet add package Microsoft.Extensions.Hosting
1516 ```
1517
1518 Now let’s dive into building your server.
1519
1520 ## Building your server
1521
1522 Open the `Program.cs` file in your project and replace its contents with the following code:
1523
1524 ```csharp theme={null}
1525 using Microsoft.Extensions.DependencyInjection;
1526 using Microsoft.Extensions.Hosting;
1527 using ModelContextProtocol;
1528 using System.Net.Http.Headers;
1529
1530 var builder = Host.CreateEmptyApplicationBuilder(settings: null);
1531
1532 builder.Services.AddMcpServer()
1533 .WithStdioServerTransport()
1534 .WithToolsFromAssembly();
1535
1536 builder.Services.AddSingleton(_ =>
1537 {
1538 var client = new HttpClient() { BaseAddress = new Uri("https://api.weather.gov") };
1539 client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("weather-tool", "1.0"));
1540 return client;
1541 });
1542
1543 var app = builder.Build();
1544
1545 await app.RunAsync();
1546 ```
1547
1548 <Note>
1549 When creating the `ApplicationHostBuilder`, ensure you use `CreateEmptyApplicationBuilder` instead of `CreateDefaultBuilder`. This ensures that the server does not write any additional messages to the console. This is only necessary for servers using STDIO transport.
1550 </Note>
1551
1552 This code sets up a basic console application that uses the Model Context Protocol SDK to create an MCP server with standard I/O transport.
1553
1554 ### Weather API helper functions
1555
1556 Create an extension class for `HttpClient` which helps simplify JSON request handling:
1557
1558 ```csharp theme={null}
1559 using System.Text.Json;
1560
1561 internal static class HttpClientExt
1562 {
1563 public static async Task<JsonDocument> ReadJsonDocumentAsync(this HttpClient client, string requestUri)
1564 {
1565 using var response = await client.GetAsync(requestUri);
1566 response.EnsureSuccessStatusCode();
1567 return await JsonDocument.ParseAsync(await response.Content.ReadAsStreamAsync());
1568 }
1569 }
1570 ```
1571
1572 Next, define a class with the tool execution handlers for querying and converting responses from the National Weather Service API:
1573
1574 ```csharp theme={null}
1575 using ModelContextProtocol.Server;
1576 using System.ComponentModel;
1577 using System.Globalization;
1578 using System.Text.Json;
1579
1580 namespace QuickstartWeatherServer.Tools;
1581
1582 [McpServerToolType]
1583 public static class WeatherTools
1584 {
1585 [McpServerTool, Description("Get weather alerts for a US state code.")]
1586 public static async Task<string> GetAlerts(
1587 HttpClient client,
1588 [Description("The US state code to get alerts for.")] string state)
1589 {
1590 using var jsonDocument = await client.ReadJsonDocumentAsync($"/alerts/active/area/{state}");
1591 var jsonElement = jsonDocument.RootElement;
1592 var alerts = jsonElement.GetProperty("features").EnumerateArray();
1593
1594 if (!alerts.Any())
1595 {
1596 return "No active alerts for this state.";
1597 }
1598
1599 return string.Join("\n--\n", alerts.Select(alert =>
1600 {
1601 JsonElement properties = alert.GetProperty("properties");
1602 return $"""
1603 Event: {properties.GetProperty("event").GetString()}
1604 Area: {properties.GetProperty("areaDesc").GetString()}
1605 Severity: {properties.GetProperty("severity").GetString()}
1606 Description: {properties.GetProperty("description").GetString()}
1607 Instruction: {properties.GetProperty("instruction").GetString()}
1608 """;
1609 }));
1610 }
1611
1612 [McpServerTool, Description("Get weather forecast for a location.")]
1613 public static async Task<string> GetForecast(
1614 HttpClient client,
1615 [Description("Latitude of the location.")] double latitude,
1616 [Description("Longitude of the location.")] double longitude)
1617 {
1618 var pointUrl = string.Create(CultureInfo.InvariantCulture, $"/points/{latitude},{longitude}");
1619 using var jsonDocument = await client.ReadJsonDocumentAsync(pointUrl);
1620 var forecastUrl = jsonDocument.RootElement.GetProperty("properties").GetProperty("forecast").GetString()
1621 ?? throw new Exception($"No forecast URL provided by {client.BaseAddress}points/{latitude},{longitude}");
1622
1623 using var forecastDocument = await client.ReadJsonDocumentAsync(forecastUrl);
1624 var periods = forecastDocument.RootElement.GetProperty("properties").GetProperty("periods").EnumerateArray();
1625
1626 return string.Join("\n---\n", periods.Select(period => $"""
1627 {period.GetProperty("name").GetString()}
1628 Temperature: {period.GetProperty("temperature").GetInt32()}°F
1629 Wind: {period.GetProperty("windSpeed").GetString()} {period.GetProperty("windDirection").GetString()}
1630 Forecast: {period.GetProperty("detailedForecast").GetString()}
1631 """));
1632 }
1633 }
1634 ```
1635
1636 ### Running the server
1637
1638 Finally, run the server using the following command:
1639
1640 ```bash theme={null}
1641 dotnet run
1642 ```
1643
1644 This will start the server and listen for incoming requests on standard input/output.
1645
1646 ## Testing your server with Claude for Desktop
1647
1648 <Note>
1649 Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
1650 </Note>
1651
1652 First, make sure you have Claude for Desktop installed. [You can install the latest version
1653 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1654 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1655 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1656
1657 <CodeGroup>
1658 ```bash macOS/Linux theme={null}
1659 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1660 ```
1661
1662 ```powershell Windows theme={null}
1663 code $env:AppData\Claude\claude_desktop_config.json
1664 ```
1665 </CodeGroup>
1666
1667 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1668 In this case, we'll add our single weather server like so:
1669
1670 <CodeGroup>
1671 ```json macOS/Linux theme={null}
1672 {
1673 "mcpServers": {
1674 "weather": {
1675 "command": "dotnet",
1676 "args": ["run", "--project", "/ABSOLUTE/PATH/TO/PROJECT", "--no-build"]
1677 }
1678 }
1679 }
1680 ```
1681
1682 ```json Windows theme={null}
1683 {
1684 "mcpServers": {
1685 "weather": {
1686 "command": "dotnet",
1687 "args": [
1688 "run",
1689 "--project",
1690 "C:\\ABSOLUTE\\PATH\\TO\\PROJECT",
1691 "--no-build"
1692 ]
1693 }
1694 }
1695 }
1696 ```
1697 </CodeGroup>
1698
1699 This tells Claude for Desktop:
1700
1701 1. There's an MCP server named "weather"
1702 2. Launch it by running `dotnet run /ABSOLUTE/PATH/TO/PROJECT`
1703 Save the file, and restart **Claude for Desktop**.
1704 </Tab>
1705
1706 <Tab title="Ruby">
1707 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby)
1708
1709 ### Prerequisite knowledge
1710
1711 This quickstart assumes you have familiarity with:
1712
1713 * Ruby
1714 * LLMs like Claude
1715
1716 ### Logging in MCP Servers
1717
1718 When implementing MCP servers, be careful about how you handle logging:
1719
1720 **For STDIO-based servers:** Never use `puts` or `print`, as they write to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1721
1722 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1723
1724 ### Best Practices
1725
1726 * Use a logging library that writes to stderr or files.
1727
1728 ### Quick Examples
1729
1730 ```ruby theme={null}
1731 # ❌ Bad (STDIO)
1732 puts "Processing request"
1733
1734 # ✅ Good (STDIO)
1735 require "logger"
1736 logger = Logger.new($stderr)
1737 logger.info("Processing request")
1738 ```
1739
1740 ### System requirements
1741
1742 * Ruby 2.7 or higher installed.
1743
1744 ### Set up your environment
1745
1746 First, let's make sure you have Ruby installed. You can check by running:
1747
1748 ```bash theme={null}
1749 ruby --version
1750 ```
1751
1752 Now, let's create and set up our project:
1753
1754 <CodeGroup>
1755 ```bash macOS/Linux theme={null}
1756 # Create a new directory for our project
1757 mkdir weather
1758 cd weather
1759
1760 # Create a Gemfile
1761 bundle init
1762
1763 # Add the MCP SDK dependency
1764 bundle add mcp
1765
1766 # Create our server file
1767 touch weather.rb
1768 ```
1769
1770 ```powershell Windows theme={null}
1771 # Create a new directory for our project
1772 mkdir weather
1773 cd weather
1774
1775 # Create a Gemfile
1776 bundle init
1777
1778 # Add the MCP SDK dependency
1779 bundle add mcp
1780
1781 # Create our server file
1782 new-item weather.rb
1783 ```
1784 </CodeGroup>
1785
1786 Now let's dive into building your server.
1787
1788 ## Building your server
1789
1790 ### Importing packages and setting up constants
1791
1792 Open `weather.rb` and add these requires and constants at the top:
1793
1794 ```ruby theme={null}
1795 require "json"
1796 require "mcp"
1797 require "net/http"
1798 require "uri"
1799
1800 NWS_API_BASE = "https://api.weather.gov"
1801 USER_AGENT = "weather-app/1.0"
1802 ```
1803
1804 The `mcp` gem provides the Model Context Protocol SDK for Ruby, with classes for server implementation and stdio transport.
1805
1806 ### Helper methods
1807
1808 Next, let's add helper methods for querying and formatting data from the National Weather Service API:
1809
1810 ```ruby theme={null}
1811 module HelperMethods
1812 def make_nws_request(url)
1813 uri = URI(url)
1814 request = Net::HTTP::Get.new(uri)
1815 request["User-Agent"] = USER_AGENT
1816 request["Accept"] = "application/geo+json"
1817
1818 response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
1819 http.request(request)
1820 end
1821
1822 raise "HTTP #{response.code}: #{response.message}" unless response.is_a?(Net::HTTPSuccess)
1823
1824 JSON.parse(response.body)
1825 end
1826
1827 def format_alert(feature)
1828 properties = feature["properties"]
1829
1830 <<~ALERT
1831 Event: #{properties["event"] || "Unknown"}
1832 Area: #{properties["areaDesc"] || "Unknown"}
1833 Severity: #{properties["severity"] || "Unknown"}
1834 Description: #{properties["description"] || "No description available"}
1835 Instructions: #{properties["instruction"] || "No specific instructions provided"}
1836 ALERT
1837 end
1838 end
1839 ```
1840
1841 ### Implementing tool execution
1842
1843 Now let's define our tool classes. Each tool subclasses `MCP::Tool` and implements the tool logic:
1844
1845 ```ruby theme={null}
1846 class GetAlerts < MCP::Tool
1847 extend HelperMethods
1848
1849 tool_name "get_alerts"
1850 description "Get weather alerts for a US state"
1851 input_schema(
1852 properties: {
1853 state: {
1854 type: "string",
1855 description: "Two-letter US state code (e.g. CA, NY)"
1856 }
1857 },
1858 required: ["state"]
1859 )
1860
1861 def self.call(state:)
1862 url = "#{NWS_API_BASE}/alerts/active/area/#{state.upcase}"
1863 data = make_nws_request(url)
1864
1865 if data["features"].empty?
1866 return MCP::Tool::Response.new([{
1867 type: "text",
1868 text: "No active alerts for this state."
1869 }])
1870 end
1871
1872 alerts = data["features"].map { |feature| format_alert(feature) }
1873 MCP::Tool::Response.new([{
1874 type: "text",
1875 text: alerts.join("\n---\n")
1876 }])
1877 end
1878 end
1879
1880 class GetForecast < MCP::Tool
1881 extend HelperMethods
1882
1883 tool_name "get_forecast"
1884 description "Get weather forecast for a location"
1885 input_schema(
1886 properties: {
1887 latitude: {
1888 type: "number",
1889 description: "Latitude of the location"
1890 },
1891 longitude: {
1892 type: "number",
1893 description: "Longitude of the location"
1894 }
1895 },
1896 required: ["latitude", "longitude"]
1897 )
1898
1899 def self.call(latitude:, longitude:)
1900 # First get the forecast grid endpoint.
1901 points_url = "#{NWS_API_BASE}/points/#{latitude},#{longitude}"
1902 points_data = make_nws_request(points_url)
1903
1904 # Get the forecast URL from the points response.
1905 forecast_url = points_data["properties"]["forecast"]
1906 forecast_data = make_nws_request(forecast_url)
1907
1908 # Format the periods into a readable forecast.
1909 periods = forecast_data["properties"]["periods"]
1910 forecasts = periods.first(5).map do |period|
1911 <<~FORECAST
1912 #{period["name"]}:
1913 Temperature: #{period["temperature"]}°#{period["temperatureUnit"]}
1914 Wind: #{period["windSpeed"]} #{period["windDirection"]}
1915 Forecast: #{period["detailedForecast"]}
1916 FORECAST
1917 end
1918
1919 MCP::Tool::Response.new([{
1920 type: "text",
1921 text: forecasts.join("\n---\n")
1922 }])
1923 end
1924 end
1925 ```
1926
1927 ### Running the server
1928
1929 Finally, initialize and run the server:
1930
1931 ```ruby theme={null}
1932 server = MCP::Server.new(
1933 name: "weather",
1934 version: "1.0.0",
1935 tools: [GetAlerts, GetForecast]
1936 )
1937
1938 transport = MCP::Server::Transports::StdioTransport.new(server)
1939 transport.open
1940 ```
1941
1942 Your server is complete! Run `bundle exec ruby weather.rb` to start the MCP server, which will listen for messages from MCP hosts.
1943
1944 Let's now test your server from an existing MCP host, Claude for Desktop.
1945
1946 ## Testing your server with Claude for Desktop
1947
1948 <Note>
1949 Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
1950 </Note>
1951
1952 First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1953
1954 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1955
1956 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1957
1958 <CodeGroup>
1959 ```bash macOS/Linux theme={null}
1960 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1961 ```
1962
1963 ```powershell Windows theme={null}
1964 code $env:AppData\Claude\claude_desktop_config.json
1965 ```
1966 </CodeGroup>
1967
1968 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1969
1970 In this case, we'll add our single weather server like so:
1971
1972 <CodeGroup>
1973 ```json macOS/Linux theme={null}
1974 {
1975 "mcpServers": {
1976 "weather": {
1977 "command": "bundle",
1978 "args": ["exec", "ruby", "weather.rb"],
1979 "cwd": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather"
1980 }
1981 }
1982 }
1983 ```
1984
1985 ```json Windows theme={null}
1986 {
1987 "mcpServers": {
1988 "weather": {
1989 "command": "bundle",
1990 "args": ["exec", "ruby", "weather.rb"],
1991 "cwd": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather"
1992 }
1993 }
1994 }
1995 ```
1996 </CodeGroup>
1997
1998 <Note>
1999 Make sure you pass in the absolute path to your project directory in the `cwd` field. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
2000 </Note>
2001
2002 This tells Claude for Desktop:
2003
2004 1. There's an MCP server named "weather"
2005 2. Launch it by running `bundle exec ruby weather.rb` in the specified directory
2006
2007 Save the file, and restart **Claude for Desktop**.
2008 </Tab>
2009
2010 <Tab title="Rust">
2011 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust)
2012
2013 ### Prerequisite knowledge
2014
2015 This quickstart assumes you have familiarity with:
2016
2017 * Rust programming language
2018 * Async/await in Rust
2019 * LLMs like Claude
2020
2021 ### Logging in MCP Servers
2022
2023 When implementing MCP servers, be careful about how you handle logging:
2024
2025 **For STDIO-based servers:** Never use `println!()` or `print!()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
2026
2027 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
2028
2029 ### Best Practices
2030
2031 * Use a logging library that writes to stderr or files, such as `tracing` or `log` in Rust.
2032 * Configure your logging framework to avoid stdout output.
2033
2034 ### Quick Examples
2035
2036 ```rust theme={null}
2037 // ❌ Bad (STDIO)
2038 println!("Processing request");
2039
2040 // ✅ Good (STDIO)
2041 eprintln!("Processing request"); // writes to stderr
2042 ```
2043
2044 ### System requirements
2045
2046 * Rust 1.70 or higher installed.
2047 * Cargo (comes with Rust installation).
2048
2049 ### Set up your environment
2050
2051 First, let's install Rust if you haven't already. You can install Rust from [rust-lang.org](https://www.rust-lang.org/tools/install):
2052
2053 <CodeGroup>
2054 ```bash macOS/Linux theme={null}
2055 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
2056 ```
2057
2058 ```powershell Windows theme={null}
2059 # Download and run rustup-init.exe from https://rustup.rs/
2060 ```
2061 </CodeGroup>
2062
2063 Verify your Rust installation:
2064
2065 ```bash theme={null}
2066 rustc --version
2067 cargo --version
2068 ```
2069
2070 Now, let's create and set up our project:
2071
2072 <CodeGroup>
2073 ```bash macOS/Linux theme={null}
2074 # Create a new Rust project
2075 cargo new weather
2076 cd weather
2077 ```
2078
2079 ```powershell Windows theme={null}
2080 # Create a new Rust project
2081 cargo new weather
2082 cd weather
2083 ```
2084 </CodeGroup>
2085
2086 Update your `Cargo.toml` to add the required dependencies:
2087
2088 ```toml Cargo.toml theme={null}
2089 [package]
2090 name = "weather"
2091 version = "0.1.0"
2092 edition = "2024"
2093
2094 [dependencies]
2095 rmcp = { version = "0.3", features = ["server", "macros", "transport-io"] }
2096 tokio = { version = "1.46", features = ["full"] }
2097 reqwest = { version = "0.12", features = ["json"] }
2098 serde = { version = "1.0", features = ["derive"] }
2099 serde_json = "1.0"
2100 anyhow = "1.0"
2101 tracing = "0.1"
2102 tracing-subscriber = { version = "0.3", features = ["env-filter", "std", "fmt"] }
2103 ```
2104
2105 Now let's dive into building your server.
2106
2107 ## Building your server
2108
2109 ### Importing packages and constants
2110
2111 Open `src/main.rs` and add these imports and constants at the top:
2112
2113 ```rust theme={null}
2114 use anyhow::Result;
2115 use rmcp::{
2116 ServerHandler, ServiceExt,
2117 handler::server::{router::tool::ToolRouter, tool::Parameters},
2118 model::*,
2119 schemars, tool, tool_handler, tool_router,
2120 };
2121 use serde::Deserialize;
2122 use serde::de::DeserializeOwned;
2123
2124 const NWS_API_BASE: &str = "https://api.weather.gov";
2125 const USER_AGENT: &str = "weather-app/1.0";
2126 ```
2127
2128 The `rmcp` crate provides the Model Context Protocol SDK for Rust, with features for server implementation, procedural macros, and stdio transport.
2129
2130 ### Data structures
2131
2132 Next, let's define the data structures for deserializing responses from the National Weather Service API:
2133
2134 ```rust theme={null}
2135 #[derive(Debug, Deserialize)]
2136 struct AlertsResponse {
2137 features: Vec<AlertFeature>,
2138 }
2139
2140 #[derive(Debug, Deserialize)]
2141 struct AlertFeature {
2142 properties: AlertProperties,
2143 }
2144
2145 #[derive(Debug, Deserialize)]
2146 struct AlertProperties {
2147 event: Option<String>,
2148 #[serde(rename = "areaDesc")]
2149 area_desc: Option<String>,
2150 severity: Option<String>,
2151 description: Option<String>,
2152 instruction: Option<String>,
2153 }
2154
2155 #[derive(Debug, Deserialize)]
2156 struct PointsResponse {
2157 properties: PointsProperties,
2158 }
2159
2160 #[derive(Debug, Deserialize)]
2161 struct PointsProperties {
2162 forecast: String,
2163 }
2164
2165 #[derive(Debug, Deserialize)]
2166 struct ForecastResponse {
2167 properties: ForecastProperties,
2168 }
2169
2170 #[derive(Debug, Deserialize)]
2171 struct ForecastProperties {
2172 periods: Vec<ForecastPeriod>,
2173 }
2174
2175 #[derive(Debug, Deserialize)]
2176 struct ForecastPeriod {
2177 name: String,
2178 temperature: i32,
2179 #[serde(rename = "temperatureUnit")]
2180 temperature_unit: String,
2181 #[serde(rename = "windSpeed")]
2182 wind_speed: String,
2183 #[serde(rename = "windDirection")]
2184 wind_direction: String,
2185 #[serde(rename = "detailedForecast")]
2186 detailed_forecast: String,
2187 }
2188 ```
2189
2190 Now define the request types that MCP clients will send:
2191
2192 ```rust theme={null}
2193 #[derive(serde::Deserialize, schemars::JsonSchema)]
2194 pub struct MCPForecastRequest {
2195 latitude: f32,
2196 longitude: f32,
2197 }
2198
2199 #[derive(serde::Deserialize, schemars::JsonSchema)]
2200 pub struct MCPAlertRequest {
2201 state: String,
2202 }
2203 ```
2204
2205 ### Helper functions
2206
2207 Add helper functions for making API requests and formatting responses:
2208
2209 ```rust theme={null}
2210 async fn make_nws_request<T: DeserializeOwned>(url: &str) -> Result<T> {
2211 let client = reqwest::Client::new();
2212 let rsp = client
2213 .get(url)
2214 .header(reqwest::header::USER_AGENT, USER_AGENT)
2215 .header(reqwest::header::ACCEPT, "application/geo+json")
2216 .send()
2217 .await?
2218 .error_for_status()?;
2219 Ok(rsp.json::<T>().await?)
2220 }
2221
2222 fn format_alert(feature: &AlertFeature) -> String {
2223 let props = &feature.properties;
2224 format!(
2225 "Event: {}\nArea: {}\nSeverity: {}\nDescription: {}\nInstructions: {}",
2226 props.event.as_deref().unwrap_or("Unknown"),
2227 props.area_desc.as_deref().unwrap_or("Unknown"),
2228 props.severity.as_deref().unwrap_or("Unknown"),
2229 props
2230 .description
2231 .as_deref()
2232 .unwrap_or("No description available"),
2233 props
2234 .instruction
2235 .as_deref()
2236 .unwrap_or("No specific instructions provided")
2237 )
2238 }
2239
2240 fn format_period(period: &ForecastPeriod) -> String {
2241 format!(
2242 "{}:\nTemperature: {}°{}\nWind: {} {}\nForecast: {}",
2243 period.name,
2244 period.temperature,
2245 period.temperature_unit,
2246 period.wind_speed,
2247 period.wind_direction,
2248 period.detailed_forecast
2249 )
2250 }
2251 ```
2252
2253 ### Implementing the Weather server and tools
2254
2255 Now let's implement the main Weather server struct with the tool handlers:
2256
2257 ```rust theme={null}
2258 pub struct Weather {
2259 tool_router: ToolRouter<Weather>,
2260 }
2261
2262 #[tool_router]
2263 impl Weather {
2264 fn new() -> Self {
2265 Self {
2266 tool_router: Self::tool_router(),
2267 }
2268 }
2269
2270 #[tool(description = "Get weather alerts for a US state.")]
2271 async fn get_alerts(
2272 &self,
2273 Parameters(MCPAlertRequest { state }): Parameters<MCPAlertRequest>,
2274 ) -> String {
2275 let url = format!(
2276 "{}/alerts/active/area/{}",
2277 NWS_API_BASE,
2278 state.to_uppercase()
2279 );
2280
2281 match make_nws_request::<AlertsResponse>(&url).await {
2282 Ok(data) => {
2283 if data.features.is_empty() {
2284 "No active alerts for this state.".to_string()
2285 } else {
2286 data.features
2287 .iter()
2288 .map(format_alert)
2289 .collect::<Vec<_>>()
2290 .join("\n---\n")
2291 }
2292 }
2293 Err(_) => "Unable to fetch alerts or no alerts found.".to_string(),
2294 }
2295 }
2296
2297 #[tool(description = "Get weather forecast for a location.")]
2298 async fn get_forecast(
2299 &self,
2300 Parameters(MCPForecastRequest {
2301 latitude,
2302 longitude,
2303 }): Parameters<MCPForecastRequest>,
2304 ) -> String {
2305 let points_url = format!("{NWS_API_BASE}/points/{latitude},{longitude}");
2306 let Ok(points_data) = make_nws_request::<PointsResponse>(&points_url).await else {
2307 return "Unable to fetch forecast data for this location.".to_string();
2308 };
2309
2310 let forecast_url = points_data.properties.forecast;
2311
2312 let Ok(forecast_data) = make_nws_request::<ForecastResponse>(&forecast_url).await else {
2313 return "Unable to fetch forecast data for this location.".to_string();
2314 };
2315
2316 let periods = &forecast_data.properties.periods;
2317 let forecast_summary: String = periods
2318 .iter()
2319 .take(5) // Next 5 periods only
2320 .map(format_period)
2321 .collect::<Vec<String>>()
2322 .join("\n---\n");
2323 forecast_summary
2324 }
2325 }
2326 ```
2327
2328 The `#[tool_router]` macro automatically generates the routing logic, and the `#[tool]` attribute marks methods as MCP tools.
2329
2330 ### Implementing the ServerHandler
2331
2332 Implement the `ServerHandler` trait to define server capabilities:
2333
2334 ```rust theme={null}
2335 #[tool_handler]
2336 impl ServerHandler for Weather {
2337 fn get_info(&self) -> ServerInfo {
2338 ServerInfo {
2339 capabilities: ServerCapabilities::builder().enable_tools().build(),
2340 ..Default::default()
2341 }
2342 }
2343 }
2344 ```
2345
2346 ### Running the server
2347
2348 Finally, implement the main function to run the server with stdio transport:
2349
2350 ```rust theme={null}
2351 #[tokio::main]
2352 async fn main() -> Result<()> {
2353 let transport = (tokio::io::stdin(), tokio::io::stdout());
2354 let service = Weather::new().serve(transport).await?;
2355 service.waiting().await?;
2356 Ok(())
2357 }
2358 ```
2359
2360 Build your server with:
2361
2362 ```bash theme={null}
2363 cargo build --release
2364 ```
2365
2366 The compiled binary will be in `target/release/weather`.
2367
2368 Let's now test your server from an existing MCP host, Claude for Desktop.
2369
2370 ## Testing your server with Claude for Desktop
2371
2372 <Note>
2373 Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
2374 </Note>
2375
2376 First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2377
2378 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2379
2380 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2381
2382 <CodeGroup>
2383 ```bash macOS/Linux theme={null}
2384 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2385 ```
2386
2387 ```powershell Windows theme={null}
2388 code $env:AppData\Claude\claude_desktop_config.json
2389 ```
2390 </CodeGroup>
2391
2392 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2393
2394 In this case, we'll add our single weather server like so:
2395
2396 <CodeGroup>
2397 ```json macOS/Linux theme={null}
2398 {
2399 "mcpServers": {
2400 "weather": {
2401 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/target/release/weather"
2402 }
2403 }
2404 }
2405 ```
2406
2407 ```json Windows theme={null}
2408 {
2409 "mcpServers": {
2410 "weather": {
2411 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\target\\release\\weather.exe"
2412 }
2413 }
2414 }
2415 ```
2416 </CodeGroup>
2417
2418 <Note>
2419 Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2420 </Note>
2421
2422 This tells Claude for Desktop:
2423
2424 1. There's an MCP server named "weather"
2425 2. Launch it by running the compiled binary at the specified path
2426
2427 Save the file, and restart **Claude for Desktop**.
2428 </Tab>
2429
2430 <Tab title="Go">
2431 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-go)
2432
2433 ### Prerequisite knowledge
2434
2435 This quickstart assumes you have familiarity with:
2436
2437 * Go
2438 * LLMs like Claude
2439
2440 ### Logging in MCP Servers
2441
2442 When implementing MCP servers, be careful about how you handle logging:
2443
2444 **For STDIO-based servers:** Never use `fmt.Println()` or `fmt.Printf()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
2445
2446 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
2447
2448 ### Best Practices
2449
2450 * Use `log.Println()` (which defaults to stderr) or a logging library that writes to stderr or files.
2451 * Use `fmt.Fprintf(os.Stderr, ...)` to write to stderr explicitly.
2452
2453 ### Quick Examples
2454
2455 ```go theme={null}
2456 // ❌ Bad (STDIO)
2457 fmt.Println("Processing request")
2458
2459 // ✅ Good (STDIO)
2460 log.Println("Processing request") // defaults to stderr
2461
2462 // ✅ Good (STDIO)
2463 fmt.Fprintln(os.Stderr, "Processing request")
2464 ```
2465
2466 ### System requirements
2467
2468 * Go 1.24 or higher installed.
2469
2470 ### Set up your environment
2471
2472 First, let's install Go if you haven't already. You can download and install Go from [go.dev](https://go.dev/dl/).
2473
2474 Verify your Go installation:
2475
2476 ```bash theme={null}
2477 go version
2478 ```
2479
2480 Now, let's create and set up our project:
2481
2482 <CodeGroup>
2483 ```bash macOS/Linux theme={null}
2484 # Create a new directory for our project
2485 mkdir weather
2486 cd weather
2487
2488 # Initialize Go module
2489 go mod init weather
2490
2491 # Install dependencies
2492 go get github.com/modelcontextprotocol/go-sdk/mcp
2493
2494 # Create our server file
2495 touch main.go
2496 ```
2497
2498 ```powershell Windows theme={null}
2499 # Create a new directory for our project
2500 md weather
2501 cd weather
2502
2503 # Initialize Go module
2504 go mod init weather
2505
2506 # Install dependencies
2507 go get github.com/modelcontextprotocol/go-sdk/mcp
2508
2509 # Create our server file
2510 new-item main.go
2511 ```
2512 </CodeGroup>
2513
2514 Now let's dive into building your server.
2515
2516 ## Building your server
2517
2518 ### Importing packages and constants
2519
2520 Add these to the top of your `main.go`:
2521
2522 ```go theme={null}
2523 package main
2524
2525 import (
2526 "cmp"
2527 "context"
2528 "encoding/json"
2529 "fmt"
2530 "io"
2531 "log"
2532 "net/http"
2533 "strings"
2534
2535 "github.com/modelcontextprotocol/go-sdk/mcp"
2536 )
2537
2538 const (
2539 NWSAPIBase = "https://api.weather.gov"
2540 UserAgent = "weather-app/1.0"
2541 )
2542 ```
2543
2544 ### Data structures
2545
2546 Next, let's define the data structures used by our tools:
2547
2548 ```go theme={null}
2549 type PointsResponse struct {
2550 Properties struct {
2551 Forecast string `json:"forecast"`
2552 } `json:"properties"`
2553 }
2554
2555 type ForecastResponse struct {
2556 Properties struct {
2557 Periods []ForecastPeriod `json:"periods"`
2558 } `json:"properties"`
2559 }
2560
2561 type ForecastPeriod struct {
2562 Name string `json:"name"`
2563 Temperature int `json:"temperature"`
2564 TemperatureUnit string `json:"temperatureUnit"`
2565 WindSpeed string `json:"windSpeed"`
2566 WindDirection string `json:"windDirection"`
2567 DetailedForecast string `json:"detailedForecast"`
2568 }
2569
2570 type AlertsResponse struct {
2571 Features []AlertFeature `json:"features"`
2572 }
2573
2574 type AlertFeature struct {
2575 Properties AlertProperties `json:"properties"`
2576 }
2577
2578 type AlertProperties struct {
2579 Event string `json:"event"`
2580 AreaDesc string `json:"areaDesc"`
2581 Severity string `json:"severity"`
2582 Description string `json:"description"`
2583 Instruction string `json:"instruction"`
2584 }
2585
2586 type ForecastInput struct {
2587 Latitude float64 `json:"latitude" jsonschema:"Latitude of the location"`
2588 Longitude float64 `json:"longitude" jsonschema:"Longitude of the location"`
2589 }
2590
2591 type AlertsInput struct {
2592 State string `json:"state" jsonschema:"Two-letter US state code (e.g. CA, NY)"`
2593 }
2594 ```
2595
2596 ### Helper functions
2597
2598 Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
2599
2600 ```go theme={null}
2601 func makeNWSRequest[T any](ctx context.Context, url string) (*T, error) {
2602 req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
2603 if err != nil {
2604 return nil, fmt.Errorf("failed to create request: %w", err)
2605 }
2606
2607 req.Header.Set("User-Agent", UserAgent)
2608 req.Header.Set("Accept", "application/geo+json")
2609
2610 client := http.DefaultClient
2611 resp, err := client.Do(req)
2612 if err != nil {
2613 return nil, fmt.Errorf("failed to make request to %s: %w", url, err)
2614 }
2615 defer resp.Body.Close()
2616
2617 if resp.StatusCode != http.StatusOK {
2618 body, _ := io.ReadAll(resp.Body)
2619 return nil, fmt.Errorf("HTTP error %d: %s", resp.StatusCode, string(body))
2620 }
2621
2622 var result T
2623 if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
2624 return nil, fmt.Errorf("failed to decode response: %w", err)
2625 }
2626
2627 return &result, nil
2628 }
2629
2630 func formatAlert(alert AlertFeature) string {
2631 props := alert.Properties
2632 event := cmp.Or(props.Event, "Unknown")
2633 areaDesc := cmp.Or(props.AreaDesc, "Unknown")
2634 severity := cmp.Or(props.Severity, "Unknown")
2635 description := cmp.Or(props.Description, "No description available")
2636 instruction := cmp.Or(props.Instruction, "No specific instructions provided")
2637
2638 return fmt.Sprintf(`
2639 Event: %s
2640 Area: %s
2641 Severity: %s
2642 Description: %s
2643 Instructions: %s
2644 `, event, areaDesc, severity, description, instruction)
2645 }
2646
2647 func formatPeriod(period ForecastPeriod) string {
2648 return fmt.Sprintf(`
2649 %s:
2650 Temperature: %d°%s
2651 Wind: %s %s
2652 Forecast: %s
2653 `, period.Name, period.Temperature, period.TemperatureUnit,
2654 period.WindSpeed, period.WindDirection, period.DetailedForecast)
2655 }
2656 ```
2657
2658 ### Implementing tool execution
2659
2660 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
2661
2662 ```go theme={null}
2663 func getForecast(ctx context.Context, req *mcp.CallToolRequest, input ForecastInput) (
2664 *mcp.CallToolResult, any, error,
2665 ) {
2666 // Get points data
2667 pointsURL := fmt.Sprintf("%s/points/%f,%f", NWSAPIBase, input.Latitude, input.Longitude)
2668 pointsData, err := makeNWSRequest[PointsResponse](ctx, pointsURL)
2669 if err != nil {
2670 return &mcp.CallToolResult{
2671 Content: []mcp.Content{
2672 &mcp.TextContent{Text: "Unable to fetch forecast data for this location."},
2673 },
2674 }, nil, nil
2675 }
2676
2677 // Get forecast data
2678 forecastURL := pointsData.Properties.Forecast
2679 if forecastURL == "" {
2680 return &mcp.CallToolResult{
2681 Content: []mcp.Content{
2682 &mcp.TextContent{Text: "Unable to fetch forecast URL."},
2683 },
2684 }, nil, nil
2685 }
2686
2687 forecastData, err := makeNWSRequest[ForecastResponse](ctx, forecastURL)
2688 if err != nil {
2689 return &mcp.CallToolResult{
2690 Content: []mcp.Content{
2691 &mcp.TextContent{Text: "Unable to fetch detailed forecast."},
2692 },
2693 }, nil, nil
2694 }
2695
2696 // Format the periods
2697 periods := forecastData.Properties.Periods
2698 if len(periods) == 0 {
2699 return &mcp.CallToolResult{
2700 Content: []mcp.Content{
2701 &mcp.TextContent{Text: "No forecast periods available."},
2702 },
2703 }, nil, nil
2704 }
2705
2706 // Show next 5 periods
2707 var forecasts []string
2708 for i := range min(5, len(periods)) {
2709 forecasts = append(forecasts, formatPeriod(periods[i]))
2710 }
2711
2712 result := strings.Join(forecasts, "\n---\n")
2713
2714 return &mcp.CallToolResult{
2715 Content: []mcp.Content{
2716 &mcp.TextContent{Text: result},
2717 },
2718 }, nil, nil
2719 }
2720
2721 func getAlerts(ctx context.Context, req *mcp.CallToolRequest, input AlertsInput) (
2722 *mcp.CallToolResult, any, error,
2723 ) {
2724 // Build alerts URL
2725 stateCode := strings.ToUpper(input.State)
2726 alertsURL := fmt.Sprintf("%s/alerts/active/area/%s", NWSAPIBase, stateCode)
2727
2728 alertsData, err := makeNWSRequest[AlertsResponse](ctx, alertsURL)
2729 if err != nil {
2730 return &mcp.CallToolResult{
2731 Content: []mcp.Content{
2732 &mcp.TextContent{Text: "Unable to fetch alerts or no alerts found."},
2733 },
2734 }, nil, nil
2735 }
2736
2737 // Check if there are any alerts
2738 if len(alertsData.Features) == 0 {
2739 return &mcp.CallToolResult{
2740 Content: []mcp.Content{
2741 &mcp.TextContent{Text: "No active alerts for this state."},
2742 },
2743 }, nil, nil
2744 }
2745
2746 // Format alerts
2747 var alerts []string
2748 for _, feature := range alertsData.Features {
2749 alerts = append(alerts, formatAlert(feature))
2750 }
2751
2752 result := strings.Join(alerts, "\n---\n")
2753
2754 return &mcp.CallToolResult{
2755 Content: []mcp.Content{
2756 &mcp.TextContent{Text: result},
2757 },
2758 }, nil, nil
2759 }
2760 ```
2761
2762 ### Running the server
2763
2764 Finally, implement the main function to run the server:
2765
2766 ```go theme={null}
2767 func main() {
2768 // Create MCP server
2769 server := mcp.NewServer(&mcp.Implementation{
2770 Name: "weather",
2771 Version: "1.0.0",
2772 }, nil)
2773
2774 // Add get_forecast tool
2775 mcp.AddTool(server, &mcp.Tool{
2776 Name: "get_forecast",
2777 Description: "Get weather forecast for a location",
2778 }, getForecast)
2779
2780 // Add get_alerts tool
2781 mcp.AddTool(server, &mcp.Tool{
2782 Name: "get_alerts",
2783 Description: "Get weather alerts for a US state",
2784 }, getAlerts)
2785
2786 // Run server on stdio transport
2787 if err := server.Run(context.Background(), &mcp.StdioTransport{}); err != nil {
2788 log.Fatal(err)
2789 }
2790 }
2791 ```
2792
2793 Build your server with:
2794
2795 ```bash theme={null}
2796 go build -o weather .
2797 ```
2798
2799 The compiled binary will be in `./weather`.
2800
2801 Let's now test your server from an existing MCP host, Claude for Desktop.
2802
2803 ## Testing your server with Claude for Desktop
2804
2805 <Note>
2806 Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
2807 </Note>
2808
2809 First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2810
2811 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2812
2813 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2814
2815 <CodeGroup>
2816 ```bash macOS/Linux theme={null}
2817 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2818 ```
2819
2820 ```powershell Windows theme={null}
2821 code $env:AppData\Claude\claude_desktop_config.json
2822 ```
2823 </CodeGroup>
2824
2825 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2826
2827 In this case, we'll add our single weather server like so:
2828
2829 <CodeGroup>
2830 ```json macOS/Linux theme={null}
2831 {
2832 "mcpServers": {
2833 "weather": {
2834 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/weather"
2835 }
2836 }
2837 }
2838 ```
2839
2840 ```json Windows theme={null}
2841 {
2842 "mcpServers": {
2843 "weather": {
2844 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\weather.exe"
2845 }
2846 }
2847 }
2848 ```
2849 </CodeGroup>
2850
2851 <Note>
2852 Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2853 </Note>
2854
2855 This tells Claude for Desktop:
2856
2857 1. There's an MCP server named "weather"
2858 2. Launch it by running the compiled binary at the specified path
2859
2860 Save the file, and restart **Claude for Desktop**.
2861 </Tab>
2862</Tabs>
2296 }
2297}
2298```
2299
2300### Running the server
2301
2302Finally, implement the main function to run the server with stdio transport:
2303
2304```rust theme={null}
2305#[tokio::main]
2306async fn main() -> Result<()> {
2307 let transport = (tokio::io::stdin(), tokio::io::stdout());
2308 let service = Weather::new().serve(transport).await?;
2309 service.waiting().await?;
2310 Ok(())
2311}
2312```
2313
2314Build your server with:
2315
2316```bash theme={null}
2317cargo build --release
2318```
2319
2320The compiled binary will be in `target/release/weather`.
2321
2322Let's now test your server from an existing MCP host, Claude for Desktop.
2323
2324## Testing your server with Claude for Desktop
2325
2326> [!NOTE]
2327>
2328> Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
2329
2330First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2331
2332We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2333
2334For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2335
2336```bash macOS/Linux theme={null}
2337code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2338```
2339
2340```powershell Windows theme={null}
2341code $env:AppData\Claude\claude_desktop_config.json
2342```
2343
2344You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2345
2346In this case, we'll add our single weather server like so:
2347
2348```json macOS/Linux theme={null}
2349{
2350 "mcpServers": {
2351 "weather": {
2352 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/target/release/weather"
2353 }
2354 }
2355}
2356```
2357
2358```json Windows theme={null}
2359{
2360 "mcpServers": {
2361 "weather": {
2362 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\target\\release\\weather.exe"
2363 }
2364 }
2365}
2366```
2367
2368> [!NOTE]
2369>
2370> Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2371
2372This tells Claude for Desktop:
2373
23741. There's an MCP server named "weather"
23752. Launch it by running the compiled binary at the specified path
2376
2377Save the file, and restart **Claude for Desktop**.
2378
2379**Go**
2380
2381Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-go)
2382
2383### Prerequisite knowledge
2384
2385This quickstart assumes you have familiarity with:
2386
2387* Go
2388* LLMs like Claude
2389
2390### Logging in MCP Servers
2391
2392When implementing MCP servers, be careful about how you handle logging:
2393
2394**For STDIO-based servers:** Never use `fmt.Println()` or `fmt.Printf()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
2395
2396**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
2397
2398### Best Practices
2399
2400* Use `log.Println()` (which defaults to stderr) or a logging library that writes to stderr or files.
2401* Use `fmt.Fprintf(os.Stderr, ...)` to write to stderr explicitly.
2402
2403### Quick Examples
2404
2405```go theme={null}
2406// ❌ Bad (STDIO)
2407fmt.Println("Processing request")
2408
2409// ✅ Good (STDIO)
2410log.Println("Processing request") // defaults to stderr
2411
2412// ✅ Good (STDIO)
2413fmt.Fprintln(os.Stderr, "Processing request")
2414```
2415
2416### System requirements
2417
2418* Go 1.24 or higher installed.
2419
2420### Set up your environment
2421
2422First, let's install Go if you haven't already. You can download and install Go from [go.dev](https://go.dev/dl/).
2423
2424Verify your Go installation:
2425
2426```bash theme={null}
2427go version
2428```
2429
2430Now, let's create and set up our project:
2431
2432```bash macOS/Linux theme={null}
2433# Create a new directory for our project
2434mkdir weather
2435cd weather
2436
2437# Initialize Go module
2438go mod init weather
2439
2440# Install dependencies
2441go get github.com/modelcontextprotocol/go-sdk/mcp
2442
2443# Create our server file
2444touch main.go
2445```
2446
2447```powershell Windows theme={null}
2448# Create a new directory for our project
2449md weather
2450cd weather
2451
2452# Initialize Go module
2453go mod init weather
2454
2455# Install dependencies
2456go get github.com/modelcontextprotocol/go-sdk/mcp
2457
2458# Create our server file
2459new-item main.go
2460```
2461
2462Now let's dive into building your server.
2463
2464## Building your server
2465
2466### Importing packages and constants
2467
2468Add these to the top of your `main.go`:
2469
2470```go theme={null}
2471package main
2472
2473import (
2474 "cmp"
2475 "context"
2476 "encoding/json"
2477 "fmt"
2478 "io"
2479 "log"
2480 "net/http"
2481 "strings"
2482
2483 "github.com/modelcontextprotocol/go-sdk/mcp"
2484)
2485
2486const (
2487 NWSAPIBase = "https://api.weather.gov"
2488 UserAgent = "weather-app/1.0"
2489)
2490```
2491
2492### Data structures
2493
2494Next, let's define the data structures used by our tools:
2495
2496```go theme={null}
2497type PointsResponse struct {
2498 Properties struct {
2499 Forecast string `json:"forecast"`
2500 } `json:"properties"`
2501}
2502
2503type ForecastResponse struct {
2504 Properties struct {
2505 Periods []ForecastPeriod `json:"periods"`
2506 } `json:"properties"`
2507}
2508
2509type ForecastPeriod struct {
2510 Name string `json:"name"`
2511 Temperature int `json:"temperature"`
2512 TemperatureUnit string `json:"temperatureUnit"`
2513 WindSpeed string `json:"windSpeed"`
2514 WindDirection string `json:"windDirection"`
2515 DetailedForecast string `json:"detailedForecast"`
2516}
2517
2518type AlertsResponse struct {
2519 Features []AlertFeature `json:"features"`
2520}
2521
2522type AlertFeature struct {
2523 Properties AlertProperties `json:"properties"`
2524}
2525
2526type AlertProperties struct {
2527 Event string `json:"event"`
2528 AreaDesc string `json:"areaDesc"`
2529 Severity string `json:"severity"`
2530 Description string `json:"description"`
2531 Instruction string `json:"instruction"`
2532}
2533
2534type ForecastInput struct {
2535 Latitude float64 `json:"latitude" jsonschema:"Latitude of the location"`
2536 Longitude float64 `json:"longitude" jsonschema:"Longitude of the location"`
2537}
2538
2539type AlertsInput struct {
2540 State string `json:"state" jsonschema:"Two-letter US state code (e.g. CA, NY)"`
2541}
2542```
2543
2544### Helper functions
2545
2546Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
2547
2548```go theme={null}
2549func makeNWSRequest[T any](ctx context.Context, url string) (*T, error) {
2550 req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
2551 if err != nil {
2552 return nil, fmt.Errorf("failed to create request: %w", err)
2553 }
2554
2555 req.Header.Set("User-Agent", UserAgent)
2556 req.Header.Set("Accept", "application/geo+json")
2557
2558 client := http.DefaultClient
2559 resp, err := client.Do(req)
2560 if err != nil {
2561 return nil, fmt.Errorf("failed to make request to %s: %w", url, err)
2562 }
2563 defer resp.Body.Close()
2564
2565 if resp.StatusCode != http.StatusOK {
2566 body, _ := io.ReadAll(resp.Body)
2567 return nil, fmt.Errorf("HTTP error %d: %s", resp.StatusCode, string(body))
2568 }
2569
2570 var result T
2571 if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
2572 return nil, fmt.Errorf("failed to decode response: %w", err)
2573 }
2574
2575 return &result, nil
2576}
2577
2578func formatAlert(alert AlertFeature) string {
2579 props := alert.Properties
2580 event := cmp.Or(props.Event, "Unknown")
2581 areaDesc := cmp.Or(props.AreaDesc, "Unknown")
2582 severity := cmp.Or(props.Severity, "Unknown")
2583 description := cmp.Or(props.Description, "No description available")
2584 instruction := cmp.Or(props.Instruction, "No specific instructions provided")
2585
2586 return fmt.Sprintf(`
2587Event: %s
2588Area: %s
2589Severity: %s
2590Description: %s
2591Instructions: %s
2592`, event, areaDesc, severity, description, instruction)
2593}
2594
2595func formatPeriod(period ForecastPeriod) string {
2596 return fmt.Sprintf(`
2597%s:
2598Temperature: %d°%s
2599Wind: %s %s
2600Forecast: %s
2601`, period.Name, period.Temperature, period.TemperatureUnit,
2602 period.WindSpeed, period.WindDirection, period.DetailedForecast)
2603}
2604```
2605
2606### Implementing tool execution
2607
2608The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
2609
2610```go theme={null}
2611func getForecast(ctx context.Context, req *mcp.CallToolRequest, input ForecastInput) (
2612 *mcp.CallToolResult, any, error,
2613) {
2614 // Get points data
2615 pointsURL := fmt.Sprintf("%s/points/%f,%f", NWSAPIBase, input.Latitude, input.Longitude)
2616 pointsData, err := makeNWSRequest[PointsResponse](ctx, pointsURL)
2617 if err != nil {
2618 return &mcp.CallToolResult{
2619 Content: []mcp.Content{
2620 &mcp.TextContent{Text: "Unable to fetch forecast data for this location."},
2621 },
2622 }, nil, nil
2623 }
2624
2625 // Get forecast data
2626 forecastURL := pointsData.Properties.Forecast
2627 if forecastURL == "" {
2628 return &mcp.CallToolResult{
2629 Content: []mcp.Content{
2630 &mcp.TextContent{Text: "Unable to fetch forecast URL."},
2631 },
2632 }, nil, nil
2633 }
2634
2635 forecastData, err := makeNWSRequest[ForecastResponse](ctx, forecastURL)
2636 if err != nil {
2637 return &mcp.CallToolResult{
2638 Content: []mcp.Content{
2639 &mcp.TextContent{Text: "Unable to fetch detailed forecast."},
2640 },
2641 }, nil, nil
2642 }
2643
2644 // Format the periods
2645 periods := forecastData.Properties.Periods
2646 if len(periods) == 0 {
2647 return &mcp.CallToolResult{
2648 Content: []mcp.Content{
2649 &mcp.TextContent{Text: "No forecast periods available."},
2650 },
2651 }, nil, nil
2652 }
2653
2654 // Show next 5 periods
2655 var forecasts []string
2656 for i := range min(5, len(periods)) {
2657 forecasts = append(forecasts, formatPeriod(periods[i]))
2658 }
2659
2660 result := strings.Join(forecasts, "\n---\n")
2661
2662 return &mcp.CallToolResult{
2663 Content: []mcp.Content{
2664 &mcp.TextContent{Text: result},
2665 },
2666 }, nil, nil
2667}
2668
2669func getAlerts(ctx context.Context, req *mcp.CallToolRequest, input AlertsInput) (
2670 *mcp.CallToolResult, any, error,
2671) {
2672 // Build alerts URL
2673 stateCode := strings.ToUpper(input.State)
2674 alertsURL := fmt.Sprintf("%s/alerts/active/area/%s", NWSAPIBase, stateCode)
2675
2676 alertsData, err := makeNWSRequest[AlertsResponse](ctx, alertsURL)
2677 if err != nil {
2678 return &mcp.CallToolResult{
2679 Content: []mcp.Content{
2680 &mcp.TextContent{Text: "Unable to fetch alerts or no alerts found."},
2681 },
2682 }, nil, nil
2683 }
2684
2685 // Check if there are any alerts
2686 if len(alertsData.Features) == 0 {
2687 return &mcp.CallToolResult{
2688 Content: []mcp.Content{
2689 &mcp.TextContent{Text: "No active alerts for this state."},
2690 },
2691 }, nil, nil
2692 }
2693
2694 // Format alerts
2695 var alerts []string
2696 for _, feature := range alertsData.Features {
2697 alerts = append(alerts, formatAlert(feature))
2698 }
2699
2700 result := strings.Join(alerts, "\n---\n")
2701
2702 return &mcp.CallToolResult{
2703 Content: []mcp.Content{
2704 &mcp.TextContent{Text: result},
2705 },
2706 }, nil, nil
2707}
2708```
2709
2710### Running the server
2711
2712Finally, implement the main function to run the server:
2713
2714```go theme={null}
2715func main() {
2716 // Create MCP server
2717 server := mcp.NewServer(&mcp.Implementation{
2718 Name: "weather",
2719 Version: "1.0.0",
2720 }, nil)
2721
2722 // Add get_forecast tool
2723 mcp.AddTool(server, &mcp.Tool{
2724 Name: "get_forecast",
2725 Description: "Get weather forecast for a location",
2726 }, getForecast)
2727
2728 // Add get_alerts tool
2729 mcp.AddTool(server, &mcp.Tool{
2730 Name: "get_alerts",
2731 Description: "Get weather alerts for a US state",
2732 }, getAlerts)
2733
2734 // Run server on stdio transport
2735 if err := server.Run(context.Background(), &mcp.StdioTransport{}); err != nil {
2736 log.Fatal(err)
2737 }
2738}
2739```
2740
2741Build your server with:
2742
2743```bash theme={null}
2744go build -o weather .
2745```
2746
2747The compiled binary will be in `./weather`.
2748
2749Let's now test your server from an existing MCP host, Claude for Desktop.
2750
2751## Testing your server with Claude for Desktop
2752
2753> [!NOTE]
2754>
2755> Claude for Desktop is not yet available on Linux. Linux users can proceed to the [Building a client](/docs/2025-11-25/develop/build-client) tutorial to build an MCP client that connects to the server we just built.
2756
2757First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2758
2759We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2760
2761For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2762
2763```bash macOS/Linux theme={null}
2764code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2765```
2766
2767```powershell Windows theme={null}
2768code $env:AppData\Claude\claude_desktop_config.json
2769```
2770
2771You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2772
2773In this case, we'll add our single weather server like so:
2774
2775```json macOS/Linux theme={null}
2776{
2777 "mcpServers": {
2778 "weather": {
2779 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/weather"
2780 }
2781 }
2782}
2783```
2784
2785```json Windows theme={null}
2786{
2787 "mcpServers": {
2788 "weather": {
2789 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\weather.exe"
2790 }
2791 }
2792}
2793```
2794
2795> [!NOTE]
2796>
2797> Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2798
2799This tells Claude for Desktop:
2800
28011. There's an MCP server named "weather"
28022. Launch it by running the compiled binary at the specified path
2803
2804Save the file, and restart **Claude for Desktop**.
28632805
28642806### Test with commands
28652807
2866Let's make sure Claude for Desktop is picking up the two tools we've exposed in our `weather` server. You can do this by looking for the "Add files, connectors, and more /" <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/claude-add-files-connectors-and-more.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=53acf21f6807dd5323b70b84b5d98d8a" style={{display: 'inline', margin: 0, height: '1.3em'}} width="33" height="33" data-path="images/claude-add-files-connectors-and-more.png" /> icon:
2867
2868<Frame>
2869 <img src="https://mintcdn.com/mcp/zNouQwo2h8cbxlDS/images/visual-indicator-mcp-tools.png?fit=max&auto=format&n=zNouQwo2h8cbxlDS&q=85&s=1bf23a2cfc5f6dd3dac1c7574cceebc9" width="684" height="133" data-path="images/visual-indicator-mcp-tools.png" />
2870</Frame>
2808Let's make sure Claude for Desktop is picking up the two tools we've exposed in our `weather` server. You can do this by looking for the "Add files, connectors, and more /"  icon:
2809
2810
28712811
28722812After clicking on the plus icon, hover over the "Connectors" menu. You should see the `weather` servers listed:
28732813
2874<Frame>
2875 <img src="https://mintcdn.com/mcp/zNouQwo2h8cbxlDS/images/available-mcp-tools.png?fit=max&auto=format&n=zNouQwo2h8cbxlDS&q=85&s=e2ace1ac88895a5fe30ebd8d01456bc3" width="437" height="244" data-path="images/available-mcp-tools.png" />
2876</Frame>
2814
28772815
28782816If your server isn't being picked up by Claude for Desktop, proceed to the [Troubleshooting](#troubleshooting) section for debugging tips.
28792817
from line 2820
28822820* What's the weather in Sacramento?
28832821* What are the active weather alerts in Texas?
28842822
2885<Frame>
2886 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/current-weather.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=dce7b2f8a06c20ba358e4bd2e75fa4c7" width="2780" height="1849" data-path="images/current-weather.png" />
2887</Frame>
2888
2889<Frame>
2890 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/weather-alerts.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=c4762bf2bd84a8781846d2965af3e4a4" width="2809" height="1850" data-path="images/weather-alerts.png" />
2891</Frame>
2892
2893<Note>
2894 Since this is the US National Weather service, the queries will only work for US locations.
2895</Note>
2823
2824
2825
2826
2827> [!NOTE]
2828>
2829> Since this is the US National Weather service, the queries will only work for US locations.
28962830
28972831## What's happening under the hood
28982832
from line 2841
29072841
29082842## Troubleshooting
29092843
2910<AccordionGroup>
2911 <Accordion title="Claude for Desktop Integration Issues">
2912 **Getting logs from Claude for Desktop**
2913
2914 Claude.app logging related to MCP is written to log files in `~/Library/Logs/Claude`:
2915
2916 * `mcp.log` will contain general logging about MCP connections and connection failures.
2917 * Files named `mcp-server-SERVERNAME.log` will contain error (stderr) logging from the named server.
2918
2919 You can run the following command to list recent logs and follow along with any new ones:
2920
2921 ```bash theme={null}
2922 # Check Claude's logs for errors
2923 tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
2924 ```
2925
2926 **Server not showing up in Claude**
2927
2928 1. Check your `claude_desktop_config.json` file syntax
2929 2. Make sure the path to your project is absolute and not relative
2930 3. Restart Claude for Desktop completely
2931
2932 <Warning>
2933 To properly restart Claude for Desktop, you must fully quit the application:
2934
2935 * **Windows**: Right-click the Claude icon in the system tray (which may be hidden in the "hidden icons" menu) and select "Quit" or "Exit".
2936 * **macOS**: Use Cmd+Q or select "Quit Claude" from the menu bar.
2937
2938 Simply closing the window does not fully quit the application, and your MCP server configuration changes will not take effect.
2939 </Warning>
2940
2941 **Tool calls failing silently**
2942
2943 If Claude attempts to use the tools but they fail:
2944
2945 1. Check Claude's logs for errors
2946 2. Verify your server builds and runs without errors
2947 3. Try restarting Claude for Desktop
2948
2949 **None of this is working. What do I do?**
2950
2951 Please refer to our [debugging guide](/docs/2025-11-25/tools/debugging) for better debugging tools and more detailed guidance.
2952 </Accordion>
2953
2954 <Accordion title="Weather API Issues">
2955 **Error: Failed to retrieve grid point data**
2956
2957 This usually means either:
2958
2959 1. The coordinates are outside the US
2960 2. The NWS API is having issues
2961 3. You're being rate limited
2962
2963 Fix:
2964
2965 * Verify you're using US coordinates
2966 * Add a small delay between requests
2967 * Check the NWS API status page
2968
2969 **Error: No active alerts for \[STATE]**
2970
2971 This isn't an error - it just means there are no current weather alerts for that state. Try a different state or check during severe weather.
2972 </Accordion>
2973</AccordionGroup>
2974
2975<Note>
2976 For more advanced troubleshooting, check out our guide on [Debugging MCP](/docs/2025-11-25/tools/debugging)
2977</Note>
2844> **Claude for Desktop Integration Issues**
2845>
2846> **Getting logs from Claude for Desktop**
2847>
2848> Claude.app logging related to MCP is written to log files in `~/Library/Logs/Claude`:
2849>
2850> * `mcp.log` will contain general logging about MCP connections and connection failures.
2851> * Files named `mcp-server-SERVERNAME.log` will contain error (stderr) logging from the named server.
2852>
2853> You can run the following command to list recent logs and follow along with any new ones:
2854>
2855> ```bash theme={null}
2856> # Check Claude's logs for errors
2857> tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
2858> ```
2859>
2860> **Server not showing up in Claude**
2861>
2862> 1. Check your `claude_desktop_config.json` file syntax
2863>
2864> 2. Make sure the path to your project is absolute and not relative
2865>
2866> 3. Restart Claude for Desktop completely
2867>
2868> > [!WARNING]
2869> >
2870> > To properly restart Claude for Desktop, you must fully quit the application:
2871> >
2872> > * **Windows**: Right-click the Claude icon in the system tray (which may be hidden in the "hidden icons" menu) and select "Quit" or "Exit".
2873> > * **macOS**: Use Cmd+Q or select "Quit Claude" from the menu bar.
2874> >
2875> > Simply closing the window does not fully quit the application, and your MCP server configuration changes will not take effect.
2876>
2877> **Tool calls failing silently**
2878>
2879> If Claude attempts to use the tools but they fail:
2880>
2881> 1. Check Claude's logs for errors
2882> 2. Verify your server builds and runs without errors
2883> 3. Try restarting Claude for Desktop
2884>
2885> **None of this is working. What do I do?**
2886>
2887> Please refer to our [debugging guide](/docs/2025-11-25/tools/debugging) for better debugging tools and more detailed guidance.
2888
2889> **Weather API Issues**
2890>
2891> **Error: Failed to retrieve grid point data**
2892>
2893> This usually means either:
2894>
2895> 1. The coordinates are outside the US
2896> 2. The NWS API is having issues
2897> 3. You're being rate limited
2898>
2899> Fix:
2900>
2901> * Verify you're using US coordinates
2902> * Add a small delay between requests
2903> * Check the NWS API status page
2904>
2905> **Error: No active alerts for \[STATE]**
2906>
2907> This isn't an error - it just means there are no current weather alerts for that state. Try a different state or check during severe weather.
2908
2909> [!NOTE]
2910>
2911> For more advanced troubleshooting, check out our guide on [Debugging MCP](/docs/2025-11-25/tools/debugging)
29782912
29792913## Next steps
29802914
2981<CardGroup cols={2}>
2982 <Card title="Building a client" icon="outlet" href="/docs/2025-11-25/develop/build-client">
2983 Learn how to build your own MCP client that can connect to your server
2984 </Card>
2985
2986 <Card title="Example servers" icon="grid" href="/examples">
2987 Check out our gallery of official MCP servers and implementations
2988 </Card>
2989
2990 <Card title="Debugging Guide" icon="bug" href="/docs/2025-11-25/tools/debugging">
2991 Learn how to effectively debug MCP servers and integrations
2992 </Card>
2993
2994 <Card title="Build with Agent Skills" icon="comments" href="/docs/2025-11-25/develop/build-with-agent-skills">
2995 Use agent skills to guide AI coding assistants through server design
2996 </Card>
2997</CardGroup>
2915> **[Building a client](/docs/2025-11-25/develop/build-client)**
2916>
2917> Learn how to build your own MCP client that can connect to your server
2918
2919> **[Example servers](/examples)**
2920>
2921> Check out our gallery of official MCP servers and implementations
2922
2923> **[Debugging Guide](/docs/2025-11-25/tools/debugging)**
2924>
2925> Learn how to effectively debug MCP servers and integrations
2926
2927> **[Build with Agent Skills](/docs/2025-11-25/develop/build-with-agent-skills)**
2928>
2929> Use agent skills to guide AI coding assistants through server design
29982930
docs/2025-11-25/develop/build-with-agent-skills Changed · +9 / -11 lines
from line 85
8585Once your agent scaffolds the server, iterate on tool descriptions and error
8686handling, then test and ship:
8787
88<CardGroup cols={2}>
89 <Card title="MCP Inspector" icon="magnifying-glass" href="/docs/2025-11-25/tools/inspector">
90 Test your server's tools, resources, and prompts interactively
91 </Card>
88> **[MCP Inspector](/docs/2025-11-25/tools/inspector)**
89>
90> Test your server's tools, resources, and prompts interactively
9291
93 <Card title="Connect to a client" icon="plug" href="/docs/2025-11-25/develop/connect-local-servers">
94 Wire your server into an MCP client via local or remote configuration
95 </Card>
92> **[Connect to a client](/docs/2025-11-25/develop/connect-local-servers)**
93>
94> Wire your server into an MCP client via local or remote configuration
9695
97 <Card title="Publish to the Registry" icon="box" href="/registry/quickstart">
98 Make your server discoverable in the MCP Registry
99 </Card>
100</CardGroup>
96> **[Publish to the Registry](/registry/quickstart)**
97>
98> Make your server discoverable in the MCP Registry
10199
docs/2025-11-25/develop/connect-local-servers Changed · +188 / -212 lines
from line 6
66
77This guide demonstrates how to connect to local MCP servers using Claude Desktop as an example, one of the many clients that support MCP. While we focus on Claude Desktop's implementation, the concepts apply broadly to other MCP-compatible clients. By the end of this tutorial, Claude will be able to interact with files on your computer, create new documents, organize folders, and search through your file system—all with your explicit permission for each action.
88
9<Frame>
10 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-filesystem.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=629d7e754dc358d71a408d6ce970c1b1" alt="Claude Desktop with filesystem integration showing file management capabilities" width="1732" height="2060" data-path="images/quickstart-filesystem.png" />
11</Frame>
9
1210
1311## Prerequisites
1412
from line 43
4543
4644The process involves configuring Claude Desktop to automatically start the Filesystem Server whenever you launch the application. This configuration is done through a JSON file that tells Claude Desktop which servers to run and how to connect to them.
4745
48<Steps>
49 <Step title="Open Claude Desktop Settings">
50 Start by accessing the Claude Desktop settings. Click on the Claude menu in your system's menu bar (not the settings within the Claude window itself) and select "Settings..."
46**1. Open Claude Desktop Settings**
5147
52 On macOS, this appears in the top menu bar:
48Start by accessing the Claude Desktop settings. Click on the Claude menu in your system's menu bar (not the settings within the Claude window itself) and select "Settings..."
5349
54 <Frame style={{ textAlign: "center" }}>
55 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-menu.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=0c8b57e0e17af3624b6762a3ea944c8e" width="400" alt="Claude Desktop menu showing Settings option" data-path="images/quickstart-menu.png" />
56 </Frame>
50On macOS, this appears in the top menu bar:
5751
58 This opens the Claude Desktop configuration window, which is separate from your Claude account settings.
59 </Step>
52
6053
61 <Step title="Access Developer Settings">
62 In the Settings window, navigate to the "Developer" tab in the left sidebar. This section contains options for configuring MCP servers and other developer features.
54This opens the Claude Desktop configuration window, which is separate from your Claude account settings.
6355
64 Click the "Edit Config" button to open the configuration file:
56**2. Access Developer Settings**
6557
66 <Frame>
67 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-developer.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=0fb595490a2f9e15c0301e771a57446c" alt="Developer settings showing Edit Config button" width="1688" height="534" data-path="images/quickstart-developer.png" />
68 </Frame>
58In the Settings window, navigate to the "Developer" tab in the left sidebar. This section contains options for configuring MCP servers and other developer features.
6959
70 This action creates a new configuration file if one doesn't exist, or opens your existing configuration. The file is located at:
60Click the "Edit Config" button to open the configuration file:
7161
72 * **macOS**: `~/Library/Application Support/Claude/claude_desktop_config.json`
73 * **Windows**: `%APPDATA%\Claude\claude_desktop_config.json`
74 </Step>
62
7563
76 <Step title="Configure the Filesystem Server">
77 Replace the contents of the configuration file with the following JSON structure. This configuration tells Claude Desktop to start the Filesystem Server with access to specific directories:
64This action creates a new configuration file if one doesn't exist, or opens your existing configuration. The file is located at:
7865
79 <CodeGroup>
80 ```json macOS theme={null}
81 {
82 "mcpServers": {
83 "filesystem": {
84 "command": "npx",
85 "args": [
86 "-y",
87 "@modelcontextprotocol/server-filesystem",
88 "/Users/username/Desktop",
89 "/Users/username/Downloads"
90 ]
91 }
92 }
93 }
94 ```
66* **macOS**: `~/Library/Application Support/Claude/claude_desktop_config.json`
67* **Windows**: `%APPDATA%\Claude\claude_desktop_config.json`
9568
96 ```json Windows theme={null}
97 {
98 "mcpServers": {
99 "filesystem": {
100 "command": "npx",
101 "args": [
102 "-y",
103 "@modelcontextprotocol/server-filesystem",
104 "C:\\Users\\username\\Desktop",
105 "C:\\Users\\username\\Downloads"
106 ]
107 }
108 }
109 }
110 ```
111 </CodeGroup>
69**3. Configure the Filesystem Server**
11270
113 Replace `username` with your actual computer username. The paths listed in the `args` array specify which directories the Filesystem Server can access. You can modify these paths or add additional directories as needed.
71Replace the contents of the configuration file with the following JSON structure. This configuration tells Claude Desktop to start the Filesystem Server with access to specific directories:
11472
115 <Tip>
116 **Understanding the Configuration**
73```json macOS theme={null}
74{
75 "mcpServers": {
76 "filesystem": {
77 "command": "npx",
78 "args": [
79 "-y",
80 "@modelcontextprotocol/server-filesystem",
81 "/Users/username/Desktop",
82 "/Users/username/Downloads"
83 ]
84 }
85 }
86}
87```
11788
118 * `"filesystem"`: A friendly name for the server that appears in Claude Desktop
119 * `"command": "npx"`: Uses Node.js's npx tool to run the server
120 * `"-y"`: Automatically confirms the installation of the server package
121 * `"@modelcontextprotocol/server-filesystem"`: The package name of the Filesystem Server
122 * The remaining arguments: Directories the server is allowed to access
123 </Tip>
89```json Windows theme={null}
90{
91 "mcpServers": {
92 "filesystem": {
93 "command": "npx",
94 "args": [
95 "-y",
96 "@modelcontextprotocol/server-filesystem",
97 "C:\\Users\\username\\Desktop",
98 "C:\\Users\\username\\Downloads"
99 ]
100 }
101 }
102}
103```
124104
125 <Warning>
126 **Security Consideration**
105Replace `username` with your actual computer username. The paths listed in the `args` array specify which directories the Filesystem Server can access. You can modify these paths or add additional directories as needed.
127106
128 Only grant access to directories you're comfortable with Claude reading and modifying. The server runs with your user account permissions, so it can perform any file operations you can perform manually.
129 </Warning>
130 </Step>
107> [!TIP]
108>
109> **Understanding the Configuration**
110>
111> * `"filesystem"`: A friendly name for the server that appears in Claude Desktop
112> * `"command": "npx"`: Uses Node.js's npx tool to run the server
113> * `"-y"`: Automatically confirms the installation of the server package
114> * `"@modelcontextprotocol/server-filesystem"`: The package name of the Filesystem Server
115> * The remaining arguments: Directories the server is allowed to access
131116
132 <Step title="Restart Claude Desktop">
133 After saving the configuration file, completely quit Claude Desktop and restart it. The application needs to restart to load the new configuration and start the MCP server.
117> [!WARNING]
118>
119> **Security Consideration**
120>
121> Only grant access to directories you're comfortable with Claude reading and modifying. The server runs with your user account permissions, so it can perform any file operations you can perform manually.
134122
135 Upon successful restart, click the "Add files, connectors and more" indicator <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/claude-add-files-connectors-and-more.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=53acf21f6807dd5323b70b84b5d98d8a" style={{display: 'inline', margin: 0, height: '1.3em'}} width="33" height="33" data-path="images/claude-add-files-connectors-and-more.png" /> in the bottom-left corner of the conversation input box:
123**4. Restart Claude Desktop**
136124
137 <Frame>
138 <img src="https://mintcdn.com/mcp/akpggzunDlIcY2im/images/quickstart-slider.png?fit=max&auto=format&n=akpggzunDlIcY2im&q=85&s=a1ebd4259cff2a7472171885f2edc035" alt="Claude Desktop interface showing MCP server indicator" width="1414" height="410" data-path="images/quickstart-slider.png" />
139 </Frame>
125After saving the configuration file, completely quit Claude Desktop and restart it. The application needs to restart to load the new configuration and start the MCP server.
140126
141 Click on this indicator, then scroll over "Connectors" and click "Manage connectors". Select "filesystem" from the connector list to view the the Filesystem Server's available tools:
127Upon successful restart, click the "Add files, connectors and more" indicator  in the bottom-left corner of the conversation input box:
142128
143 <Frame style={{ textAlign: "center" }}>
144 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-tools.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=212a63d76daba170d52db0d2f6f582be" width="400" alt="Available filesystem tools in Claude Desktop" data-path="images/quickstart-tools.png" />
145 </Frame>
129
146130
147 If the Filesystem Server doesn't connect, refer to the [Troubleshooting](#troubleshooting) section for debugging steps.
148 </Step>
149</Steps>
131Click on this indicator, then scroll over "Connectors" and click "Manage connectors". Select "filesystem" from the connector list to view the the Filesystem Server's available tools:
150132
133
134
135If the Filesystem Server doesn't connect, refer to the [Troubleshooting](#troubleshooting) section for debugging steps.
136
151137## Using the Filesystem Server
152138
153139With the Filesystem Server connected, Claude can now interact with your file system. Try these example requests to explore the capabilities:
from line 148
162148
163149Before executing any file system operation, Claude will request your approval. This ensures you maintain control over all actions:
164150
165<Frame style={{ textAlign: "center" }}>
166 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-approve.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=98cc6e9dfe885fbd6e9bfae40601e494" width="500" alt="Claude requesting approval to perform a file operation" data-path="images/quickstart-approve.png" />
167</Frame>
151
168152
169153Review each request carefully before approving. You can always deny a request if you're not comfortable with the proposed action.
170154
from line 156
172156
173157If you encounter issues setting up or using the Filesystem Server, these solutions address common problems:
174158
175<AccordionGroup>
176 <Accordion title="Server not showing up in Claude / hammer icon missing">
177 1. Restart Claude Desktop completely
178 2. Check your `claude_desktop_config.json` file syntax
179 3. Make sure the file paths included in `claude_desktop_config.json` are valid and that they are absolute and not relative
180 4. Look at [logs](#getting-logs-from-claude-for-desktop) to see why the server is not connecting
181 5. In your command line, try manually running the server (replacing `username` as you did in `claude_desktop_config.json`) to see if you get any errors:
159> **Server not showing up in Claude / hammer icon missing**
160>
161> 1. Restart Claude Desktop completely
162> 2. Check your `claude_desktop_config.json` file syntax
163> 3. Make sure the file paths included in `claude_desktop_config.json` are valid and that they are absolute and not relative
164> 4. Look at [logs](#getting-logs-from-claude-for-desktop) to see why the server is not connecting
165> 5. In your command line, try manually running the server (replacing `username` as you did in `claude_desktop_config.json`) to see if you get any errors:
166>
167> ```bash macOS/Linux theme={null}
168> npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /Users/username/Downloads
169> ```
170>
171> ```powershell Windows theme={null}
172> npx -y @modelcontextprotocol/server-filesystem C:\Users\username\Desktop C:\Users\username\Downloads
173> ```
182174
183 <CodeGroup>
184 ```bash macOS/Linux theme={null}
185 npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /Users/username/Downloads
186 ```
175> **Getting logs from Claude Desktop**
176>
177> Claude.app logging related to MCP is written to log files in:
178>
179> * macOS: `~/Library/Logs/Claude`
180>
181> * Windows: `%APPDATA%\Claude\logs`
182>
183> * `mcp.log` will contain general logging about MCP connections and connection failures.
184>
185> * Files named `mcp-server-SERVERNAME.log` will contain error (stderr) logging from the named server.
186>
187> You can run the following command to list recent logs and follow along with any new ones (on Windows, it will only show recent logs):
188>
189> ```bash macOS/Linux theme={null}
190> tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
191> ```
192>
193> ```powershell Windows theme={null}
194> type "%APPDATA%\Claude\logs\mcp*.log"
195> ```
187196
188 ```powershell Windows theme={null}
189 npx -y @modelcontextprotocol/server-filesystem C:\Users\username\Desktop C:\Users\username\Downloads
190 ```
191 </CodeGroup>
192 </Accordion>
197> **Tool calls failing silently**
198>
199> If Claude attempts to use the tools but they fail:
200>
201> 1. Check Claude's logs for errors
202> 2. Verify your server builds and runs without errors
203> 3. Try restarting Claude Desktop
193204
194 <Accordion title="Getting logs from Claude Desktop">
195 Claude.app logging related to MCP is written to log files in:
205> **None of this is working. What do I do?**
206>
207> Please refer to our [debugging guide](/docs/2025-11-25/tools/debugging) for better debugging tools and more detailed guidance.
196208
197 * macOS: `~/Library/Logs/Claude`
209> **ENOENT error and `$\{APPDATA\}` in paths on Windows**
210>
211> If your configured server fails to load, and you see within its logs an error referring to `${APPDATA}` within a path, you may need to add the expanded value of `%APPDATA%` to your `env` key in `claude_desktop_config.json`:
212>
213> ```json theme={null}
214> {
215> "brave-search": {
216> "command": "npx",
217> "args": ["-y", "@modelcontextprotocol/server-brave-search"],
218> "env": {
219> "APPDATA": "C:\\Users\\user\\AppData\\Roaming\\",
220> "BRAVE_API_KEY": "..."
221> }
222> }
223> }
224> ```
225>
226> With this change in place, launch Claude Desktop once again.
227>
228> > [!WARNING]
229> >
230> > **npm should be installed globally**
231> >
232> > The `npx` command may continue to fail if you have not installed npm globally. If npm is already installed globally, you will find `%APPDATA%\npm` exists on your system. If not, you can install npm globally by running the following command:
233> >
234> > ```bash theme={null}
235> > npm install -g npm
236> > ```
198237
199 * Windows: `%APPDATA%\Claude\logs`
200
201 * `mcp.log` will contain general logging about MCP connections and connection failures.
202
203 * Files named `mcp-server-SERVERNAME.log` will contain error (stderr) logging from the named server.
204
205 You can run the following command to list recent logs and follow along with any new ones (on Windows, it will only show recent logs):
206
207 <CodeGroup>
208 ```bash macOS/Linux theme={null}
209 tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
210 ```
211
212 ```powershell Windows theme={null}
213 type "%APPDATA%\Claude\logs\mcp*.log"
214 ```
215 </CodeGroup>
216 </Accordion>
217
218 <Accordion title="Tool calls failing silently">
219 If Claude attempts to use the tools but they fail:
220
221 1. Check Claude's logs for errors
222 2. Verify your server builds and runs without errors
223 3. Try restarting Claude Desktop
224 </Accordion>
225
226 <Accordion title="None of this is working. What do I do?">
227 Please refer to our [debugging guide](/docs/2025-11-25/tools/debugging) for better debugging tools and more detailed guidance.
228 </Accordion>
229
230 <Accordion title="ENOENT error and `${APPDATA}` in paths on Windows">
231 If your configured server fails to load, and you see within its logs an error referring to `${APPDATA}` within a path, you may need to add the expanded value of `%APPDATA%` to your `env` key in `claude_desktop_config.json`:
232
233 ```json theme={null}
234 {
235 "brave-search": {
236 "command": "npx",
237 "args": ["-y", "@modelcontextprotocol/server-brave-search"],
238 "env": {
239 "APPDATA": "C:\\Users\\user\\AppData\\Roaming\\",
240 "BRAVE_API_KEY": "..."
241 }
242 }
243 }
244 ```
245
246 With this change in place, launch Claude Desktop once again.
247
248 <Warning>
249 **npm should be installed globally**
250
251 The `npx` command may continue to fail if you have not installed npm globally. If npm is already installed globally, you will find `%APPDATA%\npm` exists on your system. If not, you can install npm globally by running the following command:
252
253 ```bash theme={null}
254 npm install -g npm
255 ```
256 </Warning>
257 </Accordion>
258</AccordionGroup>
259
260238## Next Steps
261239
262240Now that you've successfully connected Claude Desktop to a local MCP server, explore these options to expand your setup:
263241
264<CardGroup cols={2}>
265 <Card title="Explore other servers" icon="grid" href="https://github.com/modelcontextprotocol/servers">
266 Browse our collection of official and community-created MCP servers for
267 additional capabilities
268 </Card>
242> **[Explore other servers](https://github.com/modelcontextprotocol/servers)**
243>
244> Browse our collection of official and community-created MCP servers for
245> additional capabilities
269246
270 <Card title="Build your own server" icon="code" href="/docs/2025-11-25/develop/build-server">
271 Create custom MCP servers tailored to your specific workflows and
272 integrations
273 </Card>
247> **[Build your own server](/docs/2025-11-25/develop/build-server)**
248>
249> Create custom MCP servers tailored to your specific workflows and
250> integrations
274251
275 <Card title="Connect to remote servers" icon="cloud" href="/docs/2025-11-25/develop/connect-remote-servers">
276 Learn how to connect Claude to remote MCP servers for cloud-based tools and
277 services
278 </Card>
252> **[Connect to remote servers](/docs/2025-11-25/develop/connect-remote-servers)**
253>
254> Learn how to connect Claude to remote MCP servers for cloud-based tools and
255> services
279256
280 <Card title="Understand the protocol" icon="book" href="/docs/2025-11-25/learn/architecture">
281 Dive deeper into how MCP works and its architecture
282 </Card>
283</CardGroup>
257> **[Understand the protocol](/docs/2025-11-25/learn/architecture)**
258>
259> Dive deeper into how MCP works and its architecture
284260
docs/2025-11-25/develop/connect-remote-servers Changed · +41 / -57 lines
from line 25
2525
2626The process of connecting Claude to a remote MCP server involves adding a Custom Connector through the [Claude interface](https://claude.ai/). This establishes a secure connection between Claude and your chosen remote server.
2727
28<Steps>
29 <Step title="Navigate to Connector Settings">
30 Open Claude in your browser and navigate to the settings page. You can access this by clicking on your profile icon and selecting "Settings" from the dropdown menu. Once in settings, locate and click on the "Connectors" section in the sidebar.
28**1. Navigate to Connector Settings**
3129
32 This will display your currently configured connectors and provide options to add new ones.
33 </Step>
30Open Claude in your browser and navigate to the settings page. You can access this by clicking on your profile icon and selecting "Settings" from the dropdown menu. Once in settings, locate and click on the "Connectors" section in the sidebar.
3431
35 <Step title="Add a Custom Connector">
36 In the Connectors section, scroll to the bottom where you'll find the "Add custom connector" button. Click this button to begin the connection process.
32This will display your currently configured connectors and provide options to add new ones.
3733
38 <Frame>
39 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-remote/1-add-connector.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=b5ae9b23164875bbaa3aff4c178cdc64" alt="Add custom connector button in Claude settings" width="1038" height="809" data-path="images/quickstart-remote/1-add-connector.png" />
40 </Frame>
34**2. Add a Custom Connector**
4135
42 A dialog will appear prompting you to enter the remote MCP server URL. This URL should be provided by the server developer or administrator. Enter the complete URL, ensuring it includes the proper protocol (https\://) and any necessary path components.
36In the Connectors section, scroll to the bottom where you'll find the "Add custom connector" button. Click this button to begin the connection process.
4337
44 <Frame>
45 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-remote/2-connect.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=0934f16d8e016cade8e560c8f89d011b" alt="Dialog for entering remote MCP server URL" width="1616" height="282" data-path="images/quickstart-remote/2-connect.png" />
46 </Frame>
38
4739
48 After entering the URL, click "Add" to proceed with the connection.
49 </Step>
40A dialog will appear prompting you to enter the remote MCP server URL. This URL should be provided by the server developer or administrator. Enter the complete URL, ensuring it includes the proper protocol (https\://) and any necessary path components.
5041
51 <Step title="Complete Authentication">
52 Most remote MCP servers require authentication to ensure secure access to their resources. The authentication process varies depending on the server implementation but commonly involves OAuth, API keys, or username/password combinations.
42
5343
54 <Frame>
55 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-remote/3-auth.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=89af6e1b85718637231388697cc7b015" alt="Authentication screen for remote MCP server" width="490" height="806" data-path="images/quickstart-remote/3-auth.png" />
56 </Frame>
44After entering the URL, click "Add" to proceed with the connection.
5745
58 Follow the authentication prompts provided by the server. This may redirect you to a third-party authentication provider or display a form within Claude. Once authentication is complete, Claude will establish a secure connection to the remote server.
59 </Step>
46**3. Complete Authentication**
6047
61 <Step title="Access Resources and Prompts">
62 After successful connection, the remote server's resources and prompts become available in your Claude conversations. You can access these by clicking the paperclip icon in the message input area, which opens the attachment menu.
48Most remote MCP servers require authentication to ensure secure access to their resources. The authentication process varies depending on the server implementation but commonly involves OAuth, API keys, or username/password combinations.
6349
64 <Frame>
65 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-remote/4-select-resources-menu.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=e5fa85174f8acbadbd709bac66f42d5c" alt="Attachment menu showing available resources" width="735" height="378" data-path="images/quickstart-remote/4-select-resources-menu.png" />
66 </Frame>
50
6751
68 The menu displays all available resources and prompts from your connected servers. Select the items you want to include in your conversation. These resources provide Claude with context and information from your external tools.
52Follow the authentication prompts provided by the server. This may redirect you to a third-party authentication provider or display a form within Claude. Once authentication is complete, Claude will establish a secure connection to the remote server.
6953
70 <Frame>
71 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-remote/5-select-prompts-resources.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=68722669d9e18252756885c703e4f221" alt="Selecting specific resources and prompts from the menu" width="648" height="529" data-path="images/quickstart-remote/5-select-prompts-resources.png" />
72 </Frame>
73 </Step>
54**4. Access Resources and Prompts**
7455
75 <Step title="Configure Tool Permissions">
76 Remote MCP servers often expose multiple tools with varying capabilities. You can control which tools Claude is allowed to use by configuring permissions in the connector settings. This ensures Claude only performs actions you've explicitly authorized.
56After successful connection, the remote server's resources and prompts become available in your Claude conversations. You can access these by clicking the paperclip icon in the message input area, which opens the attachment menu.
7757
78 <Frame>
79 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-remote/6-configure-tools.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=5cfd8b2c5d06e7e3699eac24c68d090e" alt="Tool permission configuration interface" width="604" height="745" data-path="images/quickstart-remote/6-configure-tools.png" />
80 </Frame>
58
8159
82 Navigate back to the Connectors settings and click on your connected server. Here you can enable or disable specific tools, set usage limits, and configure other security parameters according to your needs.
83 </Step>
84</Steps>
60The menu displays all available resources and prompts from your connected servers. Select the items you want to include in your conversation. These resources provide Claude with context and information from your external tools.
8561
62
63
64**5. Configure Tool Permissions**
65
66Remote MCP servers often expose multiple tools with varying capabilities. You can control which tools Claude is allowed to use by configuring permissions in the connector settings. This ensures Claude only performs actions you've explicitly authorized.
67
68
69
70Navigate back to the Connectors settings and click on your connected server. Here you can enable or disable specific tools, set usage limits, and configure other security parameters according to your needs.
71
8672## Best Practices for Using Remote MCP Servers
8773
8874When working with remote MCP servers, consider these recommendations to ensure a secure and efficient experience:
from line 81
9581
9682Now that you've connected Claude to a remote MCP server, you can explore its capabilities in your conversations. Try using the connected tools to automate tasks, access external data, or integrate with your existing workflows.
9783
98<CardGroup cols={2}>
99 <Card title="Build your own remote server" icon="cloud" href="/docs/2025-11-25/develop/build-server">
100 Create custom remote MCP servers to integrate with proprietary tools and
101 services
102 </Card>
84> **[Build your own remote server](/docs/2025-11-25/develop/build-server)**
85>
86> Create custom remote MCP servers to integrate with proprietary tools and
87> services
10388
104 <Card title="Explore available servers" icon="grid" href="https://github.com/modelcontextprotocol/servers">
105 Browse our collection of official and community-created MCP servers
106 </Card>
89> **[Explore available servers](https://github.com/modelcontextprotocol/servers)**
90>
91> Browse our collection of official and community-created MCP servers
10792
108 <Card title="Connect local servers" icon="computer" href="/docs/2025-11-25/develop/connect-local-servers">
109 Learn how to connect Claude Desktop to local MCP servers for direct system
110 access
111 </Card>
93> **[Connect local servers](/docs/2025-11-25/develop/connect-local-servers)**
94>
95> Learn how to connect Claude Desktop to local MCP servers for direct system
96> access
11297
113 <Card title="Understand the architecture" icon="book" href="/docs/2025-11-25/learn/architecture">
114 Dive deeper into how MCP works and its architecture
115 </Card>
116</CardGroup>
98> **[Understand the architecture](/docs/2025-11-25/learn/architecture)**
99>
100> Dive deeper into how MCP works and its architecture
117101
118102Remote MCP servers unlock powerful possibilities for extending Claude's capabilities. As you become familiar with these integrations, you'll discover new ways to streamline your workflows and accomplish complex tasks more efficiently.
119103
docs/2025-11-25/getting-started/intro Changed · +19 / -27 lines
from line 6
66
77Think of MCP like a USB-C port for AI applications. Just as USB-C provides a standardized way to connect electronic devices, MCP provides a standardized way to connect AI applications to external systems.
88
9<Frame>
10 <img src="https://mintcdn.com/mcp/bEUxYpZqie0DsluH/images/mcp-simple-diagram.png?fit=max&auto=format&n=bEUxYpZqie0DsluH&q=85&s=35268aa0ad50b8c385913810e7604550" width="3840" height="1500" data-path="images/mcp-simple-diagram.png" />
11</Frame>
9
1210
1311## What can MCP enable?
1412
from line 29
3129
3230## Start Building
3331
34<CardGroup cols={2}>
35 <Card title="Build servers" icon="server" href="/docs/2025-11-25/develop/build-server">
36 Create MCP servers to expose your data and tools
37 </Card>
32> **[Build servers](/docs/2025-11-25/develop/build-server)**
33>
34> Create MCP servers to expose your data and tools
3835
39 <Card title="Build clients" icon="computer" href="/docs/2025-11-25/develop/build-client">
40 Develop applications that connect to MCP servers
41 </Card>
36> **[Build clients](/docs/2025-11-25/develop/build-client)**
37>
38> Develop applications that connect to MCP servers
4239
43 <Card title="Build MCP Apps" icon="puzzle-piece" href="/extensions/apps/overview">
44 Build interactive apps that run inside AI clients
45 </Card>
46</CardGroup>
40> **[Build MCP Apps](/extensions/apps/overview)**
41>
42> Build interactive apps that run inside AI clients
4743
4844## Learn more
4945
50<CardGroup cols={2}>
51 <Card title="Architecture" icon="book" href="/docs/2025-11-25/learn/architecture">
52 Learn the core concepts and architecture of MCP
53 </Card>
46> **[Architecture](/docs/2025-11-25/learn/architecture)**
47>
48> Learn the core concepts and architecture of MCP
5449
55 <Card title="Security" icon="lock" href="/docs/2025-11-25/tutorials/security/security_best_practices">
56 Understand the security considerations and best practices for MCP
57 </Card>
58</CardGroup>
50> **[Security](/docs/2025-11-25/tutorials/security/security_best_practices)**
51>
52> Understand the security considerations and best practices for MCP
5953
6054## Community
6155
62<CardGroup cols={2}>
63 <Card title="Contributing" icon="users" href="/community/contributing">
64 Learn how to get involved and contribute to MCP
65 </Card>
66</CardGroup>
56> **[Contributing](/community/contributing)**
57>
58> Learn how to get involved and contribute to MCP
6759
docs/2025-11-25/learn/architecture Changed · +304 / -312 lines
#### Understanding the Initialization Exchange #### How This Works in AI Applications #### Understanding the Tool Discovery Request #### Understanding the Tool Discovery Response #### How This Works in AI Applications #### Understanding the Tool Execution Request #### Key Elements of Tool Execution #### Understanding the Tool Execution Response #### How This Works in AI Applications #### Understanding Tool List Change Notifications #### Key Features of MCP Notifications #### Client Response to Notifications #### Why Notifications Matter #### How This Works in AI Applications
The two sides of this change are more than 400 edits apart, too far apart to line up, so this is the differ's own diff of it and the words inside a line are not marked.
from line 15
1515* **MCP Development Tools**: Tools for developing MCP servers and clients, including the [MCP Inspector](https://github.com/modelcontextprotocol/inspector)
1616* [MCP Reference Server Implementations](https://github.com/modelcontextprotocol/servers): Reference implementations of MCP servers.
1717
18<Note>
19 MCP focuses solely on the protocol for context exchange—it does not dictate
20 how AI applications use LLMs or manage the provided context.
21</Note>
18> [!NOTE]
19>
20> MCP focuses solely on the protocol for context exchange—it does not dictate
21> how AI applications use LLMs or manage the provided context.
2222
2323## Concepts of MCP
2424
from line 104
104104
105105#### Lifecycle management
106106
107MCP is a <Tooltip tip="A subset of MCP can be made stateless using the Streamable HTTP transport">stateful protocol</Tooltip> that requires lifecycle management. The purpose of lifecycle management is to negotiate the <Tooltip tip="Features and operations that a client or server supports, such as tools, resources, or prompts">capabilities</Tooltip> that both client and server support. Detailed information can be found in the [specification](/specification/2025-11-25/basic/lifecycle), and the [example](#example) showcases the initialization sequence.
107MCP is a stateful protocol (A subset of MCP can be made stateless using the Streamable HTTP transport) that requires lifecycle management. The purpose of lifecycle management is to negotiate the capabilities (Features and operations that a client or server supports, such as tools, resources, or prompts) that both client and server support. Detailed information can be found in the [specification](/specification/2025-11-25/basic/lifecycle), and the [example](#example) showcases the initialization sequence.
108108
109109#### Primitives
110110
from line 145
145145
146146This section provides a step-by-step walkthrough of an MCP client-server interaction, focusing on the data layer protocol. We'll demonstrate the lifecycle sequence, tool operations, and notifications using JSON-RPC 2.0 messages.
147147
148<Steps>
149 <Step title="Initialization (Lifecycle Management)">
150 MCP begins with lifecycle management through a capability negotiation handshake. As described in the [lifecycle management](#lifecycle-management) section, the client sends an `initialize` request to establish the connection and negotiate supported features.
151
152 <CodeGroup>
153 ```json Initialize Request theme={null}
148**1. Initialization (Lifecycle Management)**
149
150MCP begins with lifecycle management through a capability negotiation handshake. As described in the [lifecycle management](#lifecycle-management) section, the client sends an `initialize` request to establish the connection and negotiate supported features.
151
152```json Initialize Request theme={null}
153{
154 "jsonrpc": "2.0",
155 "id": 1,
156 "method": "initialize",
157 "params": {
158 "protocolVersion": "2025-11-25",
159 "capabilities": {
160 "elicitation": {}
161 },
162 "clientInfo": {
163 "name": "example-client",
164 "version": "1.0.0"
165 }
166 }
167}
168```
169
170```json Initialize Response theme={null}
171{
172 "jsonrpc": "2.0",
173 "id": 1,
174 "result": {
175 "protocolVersion": "2025-11-25",
176 "capabilities": {
177 "tools": {
178 "listChanged": true
179 },
180 "resources": {}
181 },
182 "serverInfo": {
183 "name": "example-server",
184 "version": "1.0.0"
185 }
186 }
187}
188```
189
190#### Understanding the Initialization Exchange
191
192The initialization process is a key part of MCP's lifecycle management and serves several critical purposes:
193
1941. **Protocol Version Negotiation**: The `protocolVersion` field (e.g., "2025-11-25") ensures both client and server are using compatible protocol versions. This prevents communication errors that could occur when different versions attempt to interact. If a mutually compatible version is not negotiated, the connection should be terminated.
195
1962. **Capability Discovery**: The `capabilities` object allows each party to declare what features they support, including which [primitives](#primitives) they can handle (tools, resources, prompts) and whether they support features like [notifications](#notifications). This enables efficient communication by avoiding unsupported operations.
197
1983. **Identity Exchange**: The `clientInfo` and `serverInfo` objects provide identification and versioning information for debugging and compatibility purposes.
199
200In this example, the capability negotiation demonstrates how MCP primitives are declared:
201
202**Client Capabilities**:
203
204* `"elicitation": {}` - The client declares it can work with user interaction requests (can receive `elicitation/create` method calls)
205
206**Server Capabilities**:
207
208* `"tools": {"listChanged": true}` - The server supports the tools primitive AND can send `tools/list_changed` notifications when its tool list changes
209* `"resources": {}` - The server also supports the resources primitive (can handle `resources/list` and `resources/read` methods)
210
211After successful initialization, the client sends a notification to indicate it's ready:
212
213```json Notification theme={null}
214{
215 "jsonrpc": "2.0",
216 "method": "notifications/initialized"
217}
218```
219
220#### How This Works in AI Applications
221
222During initialization, the AI application's MCP client manager establishes connections to configured servers and stores their capabilities for later use. The application uses this information to determine which servers can provide specific types of functionality (tools, resources, prompts) and whether they support real-time updates.
223
224```python Pseudo-code for AI application initialization theme={null}
225# Pseudo Code
226async with stdio_client(server_config) as (read, write):
227 async with ClientSession(read, write) as session:
228 init_response = await session.initialize()
229 if init_response.capabilities.tools:
230 app.register_mcp_server(session, supports_tools=True)
231 app.set_server_ready(session)
232```
233
234**2. Tool Discovery (Primitives)**
235
236Now that the connection is established, the client can discover available tools by sending a `tools/list` request. This request is fundamental to MCP's tool discovery mechanism — it allows clients to understand what tools are available on the server before attempting to use them.
237
238```json Tools List Request theme={null}
239{
240 "jsonrpc": "2.0",
241 "id": 2,
242 "method": "tools/list"
243}
244```
245
246```json Tools List Response theme={null}
247{
248 "jsonrpc": "2.0",
249 "id": 2,
250 "result": {
251 "tools": [
154252 {
155 "jsonrpc": "2.0",
156 "id": 1,
157 "method": "initialize",
158 "params": {
159 "protocolVersion": "2025-11-25",
160 "capabilities": {
161 "elicitation": {}
253 "name": "calculator_arithmetic",
254 "title": "Calculator",
255 "description": "Perform mathematical calculations including basic arithmetic, trigonometric functions, and algebraic operations",
256 "inputSchema": {
257 "type": "object",
258 "properties": {
259 "expression": {
260 "type": "string",
261 "description": "Mathematical expression to evaluate (e.g., '2 + 3 * 4', 'sin(30)', 'sqrt(16)')"
262 }
162263 },
163 "clientInfo": {
164 "name": "example-client",
165 "version": "1.0.0"
166 }
264 "required": ["expression"]
265 }
266 },
267 {
268 "name": "weather_current",
269 "title": "Weather Information",
270 "description": "Get current weather information for any location worldwide",
271 "inputSchema": {
272 "type": "object",
273 "properties": {
274 "location": {
275 "type": "string",
276 "description": "City name, address, or coordinates (latitude,longitude)"
277 },
278 "units": {
279 "type": "string",
280 "enum": ["metric", "imperial", "kelvin"],
281 "description": "Temperature units to use in response",
282 "default": "metric"
283 }
284 },
285 "required": ["location"]
167286 }
168287 }
169 ```
170
171 ```json Initialize Response theme={null}
288 ]
289 }
290}
291```
292
293#### Understanding the Tool Discovery Request
294
295The `tools/list` request is simple, containing no parameters.
296
297#### Understanding the Tool Discovery Response
298
299The response contains a `tools` array that provides comprehensive metadata about each available tool. This array-based structure allows servers to expose multiple tools simultaneously while maintaining clear boundaries between different functionalities.
300
301Each tool object in the response includes several key fields:
302
303* **`name`**: A unique identifier for the tool within the server's namespace. This serves as the primary key for tool execution and should follow a clear naming pattern (e.g., `calculator_arithmetic` rather than just `calculate`)
304* **`title`**: A human-readable display name for the tool that clients can show to users
305* **`description`**: Detailed explanation of what the tool does and when to use it
306* **`inputSchema`**: A JSON Schema that defines the expected input parameters, enabling type validation and providing clear documentation about required and optional parameters
307
308#### How This Works in AI Applications
309
310The AI application fetches available tools from all connected MCP servers and combines them into a unified tool registry that the language model can access. This allows the LLM to understand what actions it can perform and automatically generates the appropriate tool calls during conversations.
311
312```python Pseudo-code for AI application tool discovery theme={null}
313# Pseudo-code using MCP Python SDK patterns
314available_tools = []
315for session in app.mcp_server_sessions():
316 tools_response = await session.list_tools()
317 available_tools.extend(tools_response.tools)
318conversation.register_available_tools(available_tools)
319```
320
321**3. Tool Execution (Primitives)**
322
323The client can now execute a tool using the `tools/call` method. This demonstrates how MCP primitives are used in practice: after discovering available tools, the client can invoke them with appropriate arguments.
324
325#### Understanding the Tool Execution Request
326
327The `tools/call` request follows a structured format that ensures type safety and clear communication between client and server. Note that we're using the proper tool name from the discovery response (`weather_current`) rather than a simplified name:
328
329```json Tool Call Request theme={null}
330{
331 "jsonrpc": "2.0",
332 "id": 3,
333 "method": "tools/call",
334 "params": {
335 "name": "weather_current",
336 "arguments": {
337 "location": "San Francisco",
338 "units": "imperial"
339 }
340 }
341}
342```
343
344```json Tool Call Response theme={null}
345{
346 "jsonrpc": "2.0",
347 "id": 3,
348 "result": {
349 "content": [
172350 {
173 "jsonrpc": "2.0",
174 "id": 1,
175 "result": {
176 "protocolVersion": "2025-11-25",
177 "capabilities": {
178 "tools": {
179 "listChanged": true
180 },
181 "resources": {}
182 },
183 "serverInfo": {
184 "name": "example-server",
185 "version": "1.0.0"
186 }
187 }
351 "type": "text",
352 "text": "Current weather in San Francisco: 68°F, partly cloudy with light winds from the west at 8 mph. Humidity: 65%"
188353 }
189 ```
190 </CodeGroup>
191
192 #### Understanding the Initialization Exchange
193
194 The initialization process is a key part of MCP's lifecycle management and serves several critical purposes:
195
196 1. **Protocol Version Negotiation**: The `protocolVersion` field (e.g., "2025-11-25") ensures both client and server are using compatible protocol versions. This prevents communication errors that could occur when different versions attempt to interact. If a mutually compatible version is not negotiated, the connection should be terminated.
197
198 2. **Capability Discovery**: The `capabilities` object allows each party to declare what features they support, including which [primitives](#primitives) they can handle (tools, resources, prompts) and whether they support features like [notifications](#notifications). This enables efficient communication by avoiding unsupported operations.
199
200 3. **Identity Exchange**: The `clientInfo` and `serverInfo` objects provide identification and versioning information for debugging and compatibility purposes.
201
202 In this example, the capability negotiation demonstrates how MCP primitives are declared:
203
204 **Client Capabilities**:
205
206 * `"elicitation": {}` - The client declares it can work with user interaction requests (can receive `elicitation/create` method calls)
207
208 **Server Capabilities**:
209
210 * `"tools": {"listChanged": true}` - The server supports the tools primitive AND can send `tools/list_changed` notifications when its tool list changes
211 * `"resources": {}` - The server also supports the resources primitive (can handle `resources/list` and `resources/read` methods)
212
213 After successful initialization, the client sends a notification to indicate it's ready:
214
215 ```json Notification theme={null}
216 {
217 "jsonrpc": "2.0",
218 "method": "notifications/initialized"
219 }
220 ```
221
222 #### How This Works in AI Applications
223
224 During initialization, the AI application's MCP client manager establishes connections to configured servers and stores their capabilities for later use. The application uses this information to determine which servers can provide specific types of functionality (tools, resources, prompts) and whether they support real-time updates.
225
226 ```python Pseudo-code for AI application initialization theme={null}
227 # Pseudo Code
228 async with stdio_client(server_config) as (read, write):
229 async with ClientSession(read, write) as session:
230 init_response = await session.initialize()
231 if init_response.capabilities.tools:
232 app.register_mcp_server(session, supports_tools=True)
233 app.set_server_ready(session)
234 ```
235 </Step>
236
237 <Step title="Tool Discovery (Primitives)">
238 Now that the connection is established, the client can discover available tools by sending a `tools/list` request. This request is fundamental to MCP's tool discovery mechanism — it allows clients to understand what tools are available on the server before attempting to use them.
239
240 <CodeGroup>
241 ```json Tools List Request theme={null}
242 {
243 "jsonrpc": "2.0",
244 "id": 2,
245 "method": "tools/list"
246 }
247 ```
248
249 ```json Tools List Response theme={null}
250 {
251 "jsonrpc": "2.0",
252 "id": 2,
253 "result": {
254 "tools": [
255 {
256 "name": "calculator_arithmetic",
257 "title": "Calculator",
258 "description": "Perform mathematical calculations including basic arithmetic, trigonometric functions, and algebraic operations",
259 "inputSchema": {
260 "type": "object",
261 "properties": {
262 "expression": {
263 "type": "string",
264 "description": "Mathematical expression to evaluate (e.g., '2 + 3 * 4', 'sin(30)', 'sqrt(16)')"
265 }
266 },
267 "required": ["expression"]
268 }
269 },
270 {
271 "name": "weather_current",
272 "title": "Weather Information",
273 "description": "Get current weather information for any location worldwide",
274 "inputSchema": {
275 "type": "object",
276 "properties": {
277 "location": {
278 "type": "string",
279 "description": "City name, address, or coordinates (latitude,longitude)"
280 },
281 "units": {
282 "type": "string",
283 "enum": ["metric", "imperial", "kelvin"],
284 "description": "Temperature units to use in response",
285 "default": "metric"
286 }
287 },
288 "required": ["location"]
289 }
290 }
291 ]
292 }
293 }
294 ```
295 </CodeGroup>
296
297 #### Understanding the Tool Discovery Request
298
299 The `tools/list` request is simple, containing no parameters.
300
301 #### Understanding the Tool Discovery Response
302
303 The response contains a `tools` array that provides comprehensive metadata about each available tool. This array-based structure allows servers to expose multiple tools simultaneously while maintaining clear boundaries between different functionalities.
304
305 Each tool object in the response includes several key fields:
306
307 * **`name`**: A unique identifier for the tool within the server's namespace. This serves as the primary key for tool execution and should follow a clear naming pattern (e.g., `calculator_arithmetic` rather than just `calculate`)
308 * **`title`**: A human-readable display name for the tool that clients can show to users
309 * **`description`**: Detailed explanation of what the tool does and when to use it
310 * **`inputSchema`**: A JSON Schema that defines the expected input parameters, enabling type validation and providing clear documentation about required and optional parameters
311
312 #### How This Works in AI Applications
313
314 The AI application fetches available tools from all connected MCP servers and combines them into a unified tool registry that the language model can access. This allows the LLM to understand what actions it can perform and automatically generates the appropriate tool calls during conversations.
315
316 ```python Pseudo-code for AI application tool discovery theme={null}
317 # Pseudo-code using MCP Python SDK patterns
318 available_tools = []
319 for session in app.mcp_server_sessions():
320 tools_response = await session.list_tools()
321 available_tools.extend(tools_response.tools)
322 conversation.register_available_tools(available_tools)
323 ```
324 </Step>
325
326 <Step title="Tool Execution (Primitives)">
327 The client can now execute a tool using the `tools/call` method. This demonstrates how MCP primitives are used in practice: after discovering available tools, the client can invoke them with appropriate arguments.
328
329 #### Understanding the Tool Execution Request
330
331 The `tools/call` request follows a structured format that ensures type safety and clear communication between client and server. Note that we're using the proper tool name from the discovery response (`weather_current`) rather than a simplified name:
332
333 <CodeGroup>
334 ```json Tool Call Request theme={null}
335 {
336 "jsonrpc": "2.0",
337 "id": 3,
338 "method": "tools/call",
339 "params": {
340 "name": "weather_current",
341 "arguments": {
342 "location": "San Francisco",
343 "units": "imperial"
344 }
345 }
346 }
347 ```
348
349 ```json Tool Call Response theme={null}
350 {
351 "jsonrpc": "2.0",
352 "id": 3,
353 "result": {
354 "content": [
355 {
356 "type": "text",
357 "text": "Current weather in San Francisco: 68°F, partly cloudy with light winds from the west at 8 mph. Humidity: 65%"
358 }
359 ]
360 }
361 }
362 ```
363 </CodeGroup>
364
365 #### Key Elements of Tool Execution
366
367 The request structure includes several important components:
368
369 1. **`name`**: Must match exactly the tool name from the discovery response (`weather_current`). This ensures the server can correctly identify which tool to execute.
370
371 2. **`arguments`**: Contains the input parameters as defined by the tool's `inputSchema`. In this example:
372 * `location`: "San Francisco" (required parameter)
373 * `units`: "imperial" (optional parameter, defaults to "metric" if not specified)
374
375 3. **JSON-RPC Structure**: Uses standard JSON-RPC 2.0 format with unique `id` for request-response correlation.
376
377 #### Understanding the Tool Execution Response
378
379 The response demonstrates MCP's flexible content system:
380
381 1. **`content` Array**: Tool responses return an array of content objects, allowing for rich, multi-format responses (text, images, resources, etc.)
382
383 2. **Content Types**: Each content object has a `type` field. In this example, `"type": "text"` indicates plain text content, but MCP supports various content types for different use cases.
384
385 3. **Structured Output**: The response provides actionable information that the AI application can use as context for language model interactions.
386
387 This execution pattern allows AI applications to dynamically invoke server functionality and receive structured responses that can be integrated into conversations with language models.
388
389 #### How This Works in AI Applications
390
391 When the language model decides to use a tool during a conversation, the AI application intercepts the tool call, routes it to the appropriate MCP server, executes it, and returns the results back to the LLM as part of the conversation flow. This enables the LLM to access real-time data and perform actions in the external world.
392
393 ```python theme={null}
394 # Pseudo-code for AI application tool execution
395 async def handle_tool_call(conversation, tool_name, arguments):
396 session = app.find_mcp_session_for_tool(tool_name)
397 result = await session.call_tool(tool_name, arguments)
398 conversation.add_tool_result(result.content)
399 ```
400 </Step>
401
402 <Step title="Real-time Updates (Notifications)">
403 MCP supports real-time notifications that enable servers to inform clients about changes without being explicitly requested. This demonstrates the notification system, a key feature that keeps MCP connections synchronized and responsive.
404
405 #### Understanding Tool List Change Notifications
406
407 When the server's available tools change—such as when new functionality becomes available, existing tools are modified, or tools become temporarily unavailable—the server can proactively notify connected clients:
408
409 ```json Request theme={null}
410 {
411 "jsonrpc": "2.0",
412 "method": "notifications/tools/list_changed"
413 }
414 ```
415
416 #### Key Features of MCP Notifications
417
418 1. **No Response Required**: Notice there's no `id` field in the notification. This follows JSON-RPC 2.0 notification semantics where no response is expected or sent.
419
420 2. **Capability-Based**: This notification is only sent by servers that declared `"listChanged": true` in their tools capability during initialization (as shown in Step 1).
421
422 3. **Event-Driven**: The server decides when to send notifications based on internal state changes, making MCP connections dynamic and responsive.
423
424 #### Client Response to Notifications
425
426 Upon receiving this notification, the client typically reacts by requesting the updated tool list. This creates a refresh cycle that keeps the client's understanding of available tools current:
427
428 ```json Request theme={null}
429 {
430 "jsonrpc": "2.0",
431 "id": 4,
432 "method": "tools/list"
433 }
434 ```
435
436 #### Why Notifications Matter
437
438 This notification system is crucial for several reasons:
439
440 1. **Dynamic Environments**: Tools may come and go based on server state, external dependencies, or user permissions
441 2. **Efficiency**: Clients don't need to poll for changes; they're notified when updates occur
442 3. **Consistency**: Ensures clients always have accurate information about available server capabilities
443 4. **Real-time Collaboration**: Enables responsive AI applications that can adapt to changing contexts
444
445 This notification pattern extends beyond tools to other MCP primitives, enabling comprehensive real-time synchronization between clients and servers.
446
447 #### How This Works in AI Applications
448
449 When the AI application receives a notification about changed tools, it immediately refreshes its tool registry and updates the LLM's available capabilities. This ensures that ongoing conversations always have access to the most current set of tools, and the LLM can dynamically adapt to new functionality as it becomes available.
450
451 ```python theme={null}
452 # Pseudo-code for AI application notification handling
453 async def handle_tools_changed_notification(session):
454 tools_response = await session.list_tools()
455 app.update_available_tools(session, tools_response.tools)
456 if app.conversation.is_active():
457 app.conversation.notify_llm_of_new_capabilities()
458 ```
459 </Step>
460</Steps>
354 ]
355 }
356}
357```
358
359#### Key Elements of Tool Execution
360
361The request structure includes several important components:
362
3631. **`name`**: Must match exactly the tool name from the discovery response (`weather_current`). This ensures the server can correctly identify which tool to execute.
364
3652. **`arguments`**: Contains the input parameters as defined by the tool's `inputSchema`. In this example:
366 * `location`: "San Francisco" (required parameter)
367 * `units`: "imperial" (optional parameter, defaults to "metric" if not specified)
368
3693. **JSON-RPC Structure**: Uses standard JSON-RPC 2.0 format with unique `id` for request-response correlation.
370
371#### Understanding the Tool Execution Response
372
373The response demonstrates MCP's flexible content system:
374
3751. **`content` Array**: Tool responses return an array of content objects, allowing for rich, multi-format responses (text, images, resources, etc.)
376
3772. **Content Types**: Each content object has a `type` field. In this example, `"type": "text"` indicates plain text content, but MCP supports various content types for different use cases.
378
3793. **Structured Output**: The response provides actionable information that the AI application can use as context for language model interactions.
380
381This execution pattern allows AI applications to dynamically invoke server functionality and receive structured responses that can be integrated into conversations with language models.
382
383#### How This Works in AI Applications
384
385When the language model decides to use a tool during a conversation, the AI application intercepts the tool call, routes it to the appropriate MCP server, executes it, and returns the results back to the LLM as part of the conversation flow. This enables the LLM to access real-time data and perform actions in the external world.
386
387```python theme={null}
388# Pseudo-code for AI application tool execution
389async def handle_tool_call(conversation, tool_name, arguments):
390 session = app.find_mcp_session_for_tool(tool_name)
391 result = await session.call_tool(tool_name, arguments)
392 conversation.add_tool_result(result.content)
393```
394
395**4. Real-time Updates (Notifications)**
396
397MCP supports real-time notifications that enable servers to inform clients about changes without being explicitly requested. This demonstrates the notification system, a key feature that keeps MCP connections synchronized and responsive.
398
399#### Understanding Tool List Change Notifications
400
401When the server's available tools change—such as when new functionality becomes available, existing tools are modified, or tools become temporarily unavailable—the server can proactively notify connected clients:
402
403```json Request theme={null}
404{
405 "jsonrpc": "2.0",
406 "method": "notifications/tools/list_changed"
407}
408```
409
410#### Key Features of MCP Notifications
411
4121. **No Response Required**: Notice there's no `id` field in the notification. This follows JSON-RPC 2.0 notification semantics where no response is expected or sent.
413
4142. **Capability-Based**: This notification is only sent by servers that declared `"listChanged": true` in their tools capability during initialization (as shown in Step 1).
415
4163. **Event-Driven**: The server decides when to send notifications based on internal state changes, making MCP connections dynamic and responsive.
417
418#### Client Response to Notifications
419
420Upon receiving this notification, the client typically reacts by requesting the updated tool list. This creates a refresh cycle that keeps the client's understanding of available tools current:
421
422```json Request theme={null}
423{
424 "jsonrpc": "2.0",
425 "id": 4,
426 "method": "tools/list"
427}
428```
429
430#### Why Notifications Matter
431
432This notification system is crucial for several reasons:
433
4341. **Dynamic Environments**: Tools may come and go based on server state, external dependencies, or user permissions
4352. **Efficiency**: Clients don't need to poll for changes; they're notified when updates occur
4363. **Consistency**: Ensures clients always have accurate information about available server capabilities
4374. **Real-time Collaboration**: Enables responsive AI applications that can adapt to changing contexts
438
439This notification pattern extends beyond tools to other MCP primitives, enabling comprehensive real-time synchronization between clients and servers.
440
441#### How This Works in AI Applications
442
443When the AI application receives a notification about changed tools, it immediately refreshes its tool registry and updates the LLM's available capabilities. This ensures that ongoing conversations always have access to the most current set of tools, and the LLM can dynamically adapt to new functionality as it becomes available.
444
445```python theme={null}
446# Pseudo-code for AI application notification handling
447async def handle_tools_changed_notification(session):
448 tools_response = await session.list_tools()
449 app.update_available_tools(session, tools_response.tools)
450 if app.conversation.is_active():
451 app.conversation.notify_llm_of_new_capabilities()
452```
461453
docs/2025-11-25/learn/server-concepts Changed · +3 / -3 lines
from line 10
1010
1111| Feature | Explanation | Examples | Who controls it |
1212| - | - | - | - |
13| **Tools** | Functions that your LLM can actively call, and decides when to use them based on user requests. Tools can write to databases, call external APIs, modify files, or trigger other logic. | Search flights<br />Send messages<br />Create calendar events | Model |
14| **Resources** | Passive data sources that provide read-only access to information for context, such as file contents, database schemas, or API documentation. | Retrieve documents<br />Access knowledge bases<br />Read calendars | Application |
15| **Prompts** | Pre-built instruction templates that tell the model to work with specific tools and resources. | Plan a vacation<br />Summarize my meetings<br />Draft an email | User |
13| **Tools** | Functions that your LLM can actively call, and decides when to use them based on user requests. Tools can write to databases, call external APIs, modify files, or trigger other logic. | Search flights Send messages Create calendar events | Model |
14| **Resources** | Passive data sources that provide read-only access to information for context, such as file contents, database schemas, or API documentation. | Retrieve documents Access knowledge bases Read calendars | Application |
15| **Prompts** | Pre-built instruction templates that tell the model to work with specific tools and resources. | Plan a vacation Summarize my meetings Draft an email | User |
1616
1717We will use a hypothetical scenario to demonstrate the role of each of these features, and show how they can work together.
1818
docs/2025-11-25/learn/versioning Changed · +5 / -5 lines
from line 3
33The Model Context Protocol uses string-based version identifiers following the format
44`YYYY-MM-DD`, to indicate the last date backwards incompatible changes were made.
55
6<Info>
7 The protocol version will *not* be incremented when the
8 protocol is updated, as long as the changes maintain backwards compatibility. This allows
9 for incremental improvements while preserving interoperability.
10</Info>
6> [!NOTE]
7>
8> The protocol version will *not* be incremented when the
9> protocol is updated, as long as the changes maintain backwards compatibility. This allows
10> for incremental improvements while preserving interoperability.
1111
1212## Revisions
1313
docs/2025-11-25/sdk Changed · +16 / -18 lines
from line 8
88
99| SDK | Repository | Tier |
1010| :- | :- | -: |
11| <Icon icon="square-js" size={24} /> [TypeScript](https://ts.sdk.modelcontextprotocol.io) | [modelcontextprotocol/typescript-sdk](https://github.com/modelcontextprotocol/typescript-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
12| <Icon icon="python" size={24} /> [Python](https://py.sdk.modelcontextprotocol.io) | [modelcontextprotocol/python-sdk](https://github.com/modelcontextprotocol/python-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
13| <Icon icon="square-c" size={24} /> [C#](https://csharp.sdk.modelcontextprotocol.io) | [modelcontextprotocol/csharp-sdk](https://github.com/modelcontextprotocol/csharp-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
14| <Icon icon="golang" size={24} /> [Go](https://go.sdk.modelcontextprotocol.io) | [modelcontextprotocol/go-sdk](https://github.com/modelcontextprotocol/go-sdk) | <Badge color="blue" shape="pill">Tier 1</Badge> |
15| <Icon icon="java" size={24} /> [Java](https://java.sdk.modelcontextprotocol.io) | [modelcontextprotocol/java-sdk](https://github.com/modelcontextprotocol/java-sdk) | <Badge color="purple" shape="pill">Tier 2</Badge> |
16| <Icon icon="rust" size={24} /> [Rust](https://rust.sdk.modelcontextprotocol.io) | [modelcontextprotocol/rust-sdk](https://github.com/modelcontextprotocol/rust-sdk) | <Badge color="purple" shape="pill">Tier 2</Badge> |
17| <Icon icon="swift" size={24} /> Swift | [modelcontextprotocol/swift-sdk](https://github.com/modelcontextprotocol/swift-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
18| <Icon icon="gem" size={24} /> [Ruby](https://ruby.sdk.modelcontextprotocol.io) | [modelcontextprotocol/ruby-sdk](https://github.com/modelcontextprotocol/ruby-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
19| <Icon icon="php" size={24} /> [PHP](https://php.sdk.modelcontextprotocol.io) | [modelcontextprotocol/php-sdk](https://github.com/modelcontextprotocol/php-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
20| <Icon icon="square-k" size={24} /> [Kotlin](https://kotlin.sdk.modelcontextprotocol.io) | [modelcontextprotocol/kotlin-sdk](https://github.com/modelcontextprotocol/kotlin-sdk) | <Badge color="orange" shape="pill">Tier 3</Badge> |
11| [TypeScript](https://ts.sdk.modelcontextprotocol.io) | [modelcontextprotocol/typescript-sdk](https://github.com/modelcontextprotocol/typescript-sdk) | Tier 1 |
12| [Python](https://py.sdk.modelcontextprotocol.io) | [modelcontextprotocol/python-sdk](https://github.com/modelcontextprotocol/python-sdk) | Tier 1 |
13| [C#](https://csharp.sdk.modelcontextprotocol.io) | [modelcontextprotocol/csharp-sdk](https://github.com/modelcontextprotocol/csharp-sdk) | Tier 1 |
14| [Go](https://go.sdk.modelcontextprotocol.io) | [modelcontextprotocol/go-sdk](https://github.com/modelcontextprotocol/go-sdk) | Tier 1 |
15| [Java](https://java.sdk.modelcontextprotocol.io) | [modelcontextprotocol/java-sdk](https://github.com/modelcontextprotocol/java-sdk) | Tier 2 |
16| [Rust](https://rust.sdk.modelcontextprotocol.io) | [modelcontextprotocol/rust-sdk](https://github.com/modelcontextprotocol/rust-sdk) | Tier 2 |
17| Swift | [modelcontextprotocol/swift-sdk](https://github.com/modelcontextprotocol/swift-sdk) | Tier 3 |
18| [Ruby](https://ruby.sdk.modelcontextprotocol.io) | [modelcontextprotocol/ruby-sdk](https://github.com/modelcontextprotocol/ruby-sdk) | Tier 3 |
19| [PHP](https://php.sdk.modelcontextprotocol.io) | [modelcontextprotocol/php-sdk](https://github.com/modelcontextprotocol/php-sdk) | Tier 3 |
20| [Kotlin](https://kotlin.sdk.modelcontextprotocol.io) | [modelcontextprotocol/kotlin-sdk](https://github.com/modelcontextprotocol/kotlin-sdk) | Tier 3 |
2121
2222See [SDK Tiering System](/community/sdk-tiers) for details on what each tier means.
2323
from line 36
3636
3737Ready to start building with MCP? Choose your path:
3838
39<CardGroup cols={2}>
40 <Card title="Build a Server" icon="server" href="/docs/2025-11-25/develop/build-server">
41 Learn how to create your first MCP server
42 </Card>
39> **[Build a Server](/docs/2025-11-25/develop/build-server)**
40>
41> Learn how to create your first MCP server
4342
44 <Card title="Build a Client" icon="computer" href="/docs/2025-11-25/develop/build-client">
45 Create applications that connect to MCP servers
46 </Card>
47</CardGroup>
43> **[Build a Client](/docs/2025-11-25/develop/build-client)**
44>
45> Create applications that connect to MCP servers
4846
docs/2025-11-25/tools/debugging Changed · +46 / -54 lines
from line 32
3232logged to stderr (standard error) will be captured by the host application
3333automatically.
3434
35<Warning>
36 Local MCP servers should not log messages to stdout (standard out), as this
37 will interfere with protocol operation.
38</Warning>
35> [!WARNING]
36>
37> Local MCP servers should not log messages to stdout (standard out), as this
38> will interfere with protocol operation.
3939
4040For servers using the
4141[Streamable HTTP transport](/specification/2025-11-25/basic/transports#streamable-http),
from line 48
4848For all [transports](/specification/2025-11-25/basic/transports), you can also
4949provide logging to the client by sending a log message notification:
5050
51<CodeGroup>
52 ```python Python theme={null}
53 @server.tool()
54 async def my_tool(ctx: Context) -> str:
55 await ctx.session.send_log_message(
56 level="info",
57 data="Server started successfully",
58 )
59 return "done"
60 ```
51```python Python theme={null}
52@server.tool()
53async def my_tool(ctx: Context) -> str:
54 await ctx.session.send_log_message(
55 level="info",
56 data="Server started successfully",
57 )
58 return "done"
59```
6160
62 ```typescript TypeScript theme={null}
63 await server.sendLoggingMessage({
64 level: "info",
65 data: "Server started successfully",
66 });
67 ```
68</CodeGroup>
61```typescript TypeScript theme={null}
62await server.sendLoggingMessage({
63 level: "info",
64 data: "Server started successfully",
65});
66```
6967
7068MCP defines eight
7169[RFC 5424 severity levels](/specification/2025-11-25/server/utilities/logging#log-levels)
from line 189
191189hover over the **Connectors** menu to see connected servers and available
192190tools.
193191
194<img src="https://mintcdn.com/mcp/zNouQwo2h8cbxlDS/images/available-mcp-tools.png?fit=max&auto=format&n=zNouQwo2h8cbxlDS&q=85&s=e2ace1ac88895a5fe30ebd8d01456bc3" alt="Available MCP tools" width="437" height="244" data-path="images/available-mcp-tools.png" />
192
195193
196194### Viewing logs
197195
from line 198
200198* macOS: `~/Library/Logs/Claude`
201199* Windows: `%APPDATA%\Claude\logs`
202200
203<CodeGroup>
204 ```bash macOS theme={null}
205 tail -n 20 -F ~/Library/Logs/Claude/mcp*.log
206 ```
201```bash macOS theme={null}
202tail -n 20 -F ~/Library/Logs/Claude/mcp*.log
203```
207204
208 ```powershell Windows theme={null}
209 type "$env:AppData\Claude\logs\mcp*.log"
210 ```
211</CodeGroup>
205```powershell Windows theme={null}
206type "$env:AppData\Claude\logs\mcp*.log"
207```
212208
213209The logs capture:
214210
from line 220
224220
2252211. Create a `developer_settings.json` file with `allowDevTools` set to true:
226222
227<CodeGroup>
228 ```bash macOS theme={null}
229 echo '{"allowDevTools": true}' > ~/Library/Application\ Support/Claude/developer_settings.json
230 ```
223```bash macOS theme={null}
224echo '{"allowDevTools": true}' > ~/Library/Application\ Support/Claude/developer_settings.json
225```
231226
232 ```powershell Windows theme={null}
233 '{"allowDevTools": true}' | Set-Content "$env:AppData\Claude\developer_settings.json"
234 ```
235</CodeGroup>
227```powershell Windows theme={null}
228'{"allowDevTools": true}' | Set-Content "$env:AppData\Claude\developer_settings.json"
229```
236230
2372312. Open DevTools: `Command-Option-I` (macOS) or `Ctrl+Alt+I` (Windows)
238232
from line 327
333327
334328## Next steps
335329
336<CardGroup cols={2}>
337 <Card title="MCP Inspector" icon="magnifying-glass" href="/docs/2025-11-25/tools/inspector">
338 Learn to use the MCP Inspector
339 </Card>
330> **[MCP Inspector](/docs/2025-11-25/tools/inspector)**
331>
332> Learn to use the MCP Inspector
340333
341 <Card title="Build an MCP server" icon="code" href="/docs/2025-11-25/develop/build-server">
342 Walk through building a server from scratch
343 </Card>
334> **[Build an MCP server](/docs/2025-11-25/develop/build-server)**
335>
336> Walk through building a server from scratch
344337
345 <Card title="Connect local servers" icon="plug" href="/docs/2025-11-25/develop/connect-local-servers">
346 Full claude\_desktop\_config.json reference and troubleshooting
347 </Card>
348</CardGroup>
338> **[Connect local servers](/docs/2025-11-25/develop/connect-local-servers)**
339>
340> Full claude\_desktop\_config.json reference and troubleshooting
349341
docs/2025-11-25/tools/inspector Changed · +36 / -44 lines
from line 22
2222
2323A common way to start server packages from [npm](https://npmjs.com) or [PyPI](https://pypi.org).
2424
25<Tabs>
26 <Tab title="npm package">
27 ```bash theme={null}
28 npx -y @modelcontextprotocol/inspector npx <package-name> <args>
29 # For example
30 npx -y @modelcontextprotocol/inspector npx @modelcontextprotocol/server-filesystem /Users/username/Desktop
31 ```
32 </Tab>
25**npm package**
3326
34 <Tab title="PyPI package">
35 ```bash theme={null}
36 npx @modelcontextprotocol/inspector uvx <package-name> <args>
37 # For example
38 npx @modelcontextprotocol/inspector uvx mcp-server-git --repository ~/code/mcp/servers.git
39 ```
40 </Tab>
41</Tabs>
27```bash theme={null}
28npx -y @modelcontextprotocol/inspector npx <package-name> <args>
29# For example
30npx -y @modelcontextprotocol/inspector npx @modelcontextprotocol/server-filesystem /Users/username/Desktop
31```
4232
33**PyPI package**
34
35```bash theme={null}
36npx @modelcontextprotocol/inspector uvx <package-name> <args>
37# For example
38npx @modelcontextprotocol/inspector uvx mcp-server-git --repository ~/code/mcp/servers.git
39```
40
4341#### Inspecting locally developed servers
4442
4543To inspect servers locally developed or downloaded as a repository, the most common
4644way is:
4745
48<Tabs>
49 <Tab title="TypeScript">
50 ```bash theme={null}
51 npx @modelcontextprotocol/inspector node path/to/server/index.js args...
52 ```
53 </Tab>
46**TypeScript**
5447
55 <Tab title="Python">
56 ```bash theme={null}
57 npx @modelcontextprotocol/inspector \
58 uv \
59 --directory path/to/server \
60 run \
61 package-name \
62 args...
63 ```
64 </Tab>
65</Tabs>
48```bash theme={null}
49npx @modelcontextprotocol/inspector node path/to/server/index.js args...
50```
6651
52**Python**
53
54```bash theme={null}
55npx @modelcontextprotocol/inspector \
56 uv \
57 --directory path/to/server \
58 run \
59 package-name \
60 args...
61```
62
6763Please carefully read any attached README for the most accurate instructions.
6864
6965## Feature overview
7066
71<Frame caption="The MCP Inspector interface">
72 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/mcp-inspector.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=83b12e2a457c96ef4ad17c7357236290" width="2888" height="1761" data-path="images/mcp-inspector.png" />
73</Frame>
67
7468
7569The Inspector provides several features for interacting with your MCP server:
7670
from line 123
129123
130124## Next steps
131125
132<CardGroup cols={2}>
133 <Card title="Inspector Repository" icon="github" href="https://github.com/modelcontextprotocol/inspector">
134 Check out the MCP Inspector source code
135 </Card>
126> **[Inspector Repository](https://github.com/modelcontextprotocol/inspector)**
127>
128> Check out the MCP Inspector source code
136129
137 <Card title="Debugging Guide" icon="bug" href="/docs/2025-11-25/tools/debugging">
138 Learn about broader debugging strategies
139 </Card>
140</CardGroup>
130> **[Debugging Guide](/docs/2025-11-25/tools/debugging)**
131>
132> Learn about broader debugging strategies
141133
docs/2025-11-25/tutorials/security/authorization Changed · +841 / -861 lines
The two sides of this change are more than 400 edits apart, too far apart to line up, so this is the differ's own diff of it and the words inside a line are not marked.
from line 16
1616* You're building for enterprise environments with strict access controls
1717* You want to implement rate limiting or usage tracking per user
1818
19<Tip>
20 **Authorization for Local MCP Servers**
21
22 For MCP servers using the [STDIO transport](/specification/2025-11-25/basic/transports#stdio), you can use environment-based credentials or credentials provided by third-party libraries embedded directly in the MCP server instead. Because a STDIO-built MCP server runs locally, it has access to a range of flexible options when it comes to acquiring user credentials that may or may not rely on in-browser authentication and authorization flows.
23
24 OAuth flows, in turn, are designed for HTTP-based transports where the MCP server is remotely-hosted and the client uses OAuth to establish that a user is authorized to access said remote server.
25</Tip>
19> [!TIP]
20>
21> **Authorization for Local MCP Servers**
22>
23> For MCP servers using the [STDIO transport](/specification/2025-11-25/basic/transports#stdio), you can use environment-based credentials or credentials provided by third-party libraries embedded directly in the MCP server instead. Because a STDIO-built MCP server runs locally, it has access to a range of flexible options when it comes to acquiring user credentials that may or may not rely on in-browser authentication and authorization flows.
24>
25> OAuth flows, in turn, are designed for HTTP-based transports where the MCP server is remotely-hosted and the client uses OAuth to establish that a user is authorized to access said remote server.
2626
2727## The Authorization Flow: Step by Step
2828
2929Let's walk through what happens when a client wants to connect to your protected MCP server:
3030
31<Steps>
32 <Step title="Initial Handshake">
33 When your MCP client first tries to connect, your server responds with a `401 Unauthorized` and tells the client where to find authorization information, captured in a [Protected Resource Metadata (PRM) document](https://datatracker.ietf.org/doc/html/rfc9728). The document is hosted by the MCP server, follows a predictable path pattern, and is provided to the client in the `resource_metadata` parameter within the `WWW-Authenticate` header.
34
35 ```http theme={null}
36 HTTP/1.1 401 Unauthorized
37 WWW-Authenticate: Bearer realm="mcp",
38 resource_metadata="https://your-server.com/.well-known/oauth-protected-resource"
39 ```
40
41 This tells the client that authorization is required for the MCP server and where to get the necessary information to kickstart the authorization flow.
42 </Step>
43
44 <Step title="Protected Resource Metadata Discovery">
45 With the URI pointer to the PRM document, the client will fetch the metadata to learn about the authorization server, supported scopes, and other resource information. The data is typically encapsulated in a JSON blob, similar to the one below.
46
47 ```json theme={null}
48 {
49 "resource": "https://your-server.com/mcp",
50 "authorization_servers": ["https://auth.your-server.com"],
51 "scopes_supported": ["mcp:tools", "mcp:resources"]
52 }
53 ```
54
55 You can see a more comprehensive example in [RFC 9728 Section 3.2](https://datatracker.ietf.org/doc/html/rfc9728#name-protected-resource-metadata-r).
56 </Step>
57
58 <Step title="Authorization Server Discovery">
59 Next, the client discovers what the authorization server can do by fetching its metadata. If the PRM document lists more than one authorization server, the client can decide which one to use.
60
61 With an authorization server selected, the client will then construct a standard metadata URI and issue a request to the [OpenID Connect (OIDC) Discovery](https://openid.net/specs/openid-connect-discovery-1_0.html) or [OAuth 2.0 Auth Server Metadata](https://datatracker.ietf.org/doc/html/rfc8414) endpoints (depending on authorization server support)
62 and retrieve another set of metadata properties that will allow it to know the endpoints it needs to complete the authorization flow.
63
64 ```json theme={null}
65 {
66 "issuer": "https://auth.your-server.com",
67 "authorization_endpoint": "https://auth.your-server.com/authorize",
68 "token_endpoint": "https://auth.your-server.com/token",
69 "registration_endpoint": "https://auth.your-server.com/register"
70 }
71 ```
72 </Step>
73
74 <Step title="Client Registration">
75 With all the metadata out of the way, the client now needs to make sure that it's registered with the authorization server. This can be done in two ways.
76
77 First, the client can be **pre-registered** with a given authorization server, in which case it can have embedded client registration information that it uses to complete the authorization flow.
78
79 Alternatively, the client can use **Dynamic Client Registration** (DCR) to dynamically register itself with the authorization server. The latter scenario requires the authorization server to support DCR. If the authorization server does support DCR, the client will send a request to the `registration_endpoint` with its information:
80
81 ```json theme={null}
82 {
83 "client_name": "My MCP Client",
84 "redirect_uris": ["http://localhost:3000/callback"],
85 "grant_types": ["authorization_code", "refresh_token"],
86 "response_types": ["code"]
87 }
88 ```
89
90 If the registration succeeds, the authorization server will return a JSON blob with client registration information.
91
92 <Tip>
93 **No DCR or Pre-Registration**
94
95 In case an MCP client connects to an MCP server that doesn't use an authorization server that supports DCR and the client is not pre-registered with said authorization server, it's the responsibility of the client developer to provide an affordance for the end-user to enter client information manually.
96 </Tip>
97 </Step>
98
99 <Step title="User Authorization">
100 The client will now need to open a browser to the `/authorize` endpoint, where the user can log in and grant the required permissions. The authorization server will then redirect back to the client with an authorization code that the client exchanges for tokens:
101
102 ```json theme={null}
103 {
104 "access_token": "eyJhbGciOiJSUzI1NiIs...",
105 "refresh_token": "def502...",
106 "token_type": "Bearer",
107 "expires_in": 3600
108 }
109 ```
110
111 The access token is what the client will use to authenticate requests to the MCP server. This step follows standard [OAuth 2.1 authorization code with PKCE](https://oauth.net/2/grant-types/authorization-code/) conventions.
112 </Step>
113
114 <Step title="Making Authenticated Requests">
115 Finally, the client can make requests to your MCP server using the access token embedded in the `Authorization` header:
116
117 ```http theme={null}
118 GET /mcp HTTP/1.1
119 Host: your-server.com
120 Authorization: Bearer eyJhbGciOiJSUzI1NiIs...
121 ```
122
123 The MCP server will need to validate the token and process the request if the token is valid and has the required permissions.
124 </Step>
125</Steps>
31**1. Initial Handshake**
32
33When your MCP client first tries to connect, your server responds with a `401 Unauthorized` and tells the client where to find authorization information, captured in a [Protected Resource Metadata (PRM) document](https://datatracker.ietf.org/doc/html/rfc9728). The document is hosted by the MCP server, follows a predictable path pattern, and is provided to the client in the `resource_metadata` parameter within the `WWW-Authenticate` header.
34
35```http theme={null}
36HTTP/1.1 401 Unauthorized
37WWW-Authenticate: Bearer realm="mcp",
38 resource_metadata="https://your-server.com/.well-known/oauth-protected-resource"
39```
40
41This tells the client that authorization is required for the MCP server and where to get the necessary information to kickstart the authorization flow.
42
43**2. Protected Resource Metadata Discovery**
44
45With the URI pointer to the PRM document, the client will fetch the metadata to learn about the authorization server, supported scopes, and other resource information. The data is typically encapsulated in a JSON blob, similar to the one below.
46
47```json theme={null}
48{
49 "resource": "https://your-server.com/mcp",
50 "authorization_servers": ["https://auth.your-server.com"],
51 "scopes_supported": ["mcp:tools", "mcp:resources"]
52}
53```
54
55You can see a more comprehensive example in [RFC 9728 Section 3.2](https://datatracker.ietf.org/doc/html/rfc9728#name-protected-resource-metadata-r).
56
57**3. Authorization Server Discovery**
58
59Next, the client discovers what the authorization server can do by fetching its metadata. If the PRM document lists more than one authorization server, the client can decide which one to use.
60
61With an authorization server selected, the client will then construct a standard metadata URI and issue a request to the [OpenID Connect (OIDC) Discovery](https://openid.net/specs/openid-connect-discovery-1_0.html) or [OAuth 2.0 Auth Server Metadata](https://datatracker.ietf.org/doc/html/rfc8414) endpoints (depending on authorization server support)
62and retrieve another set of metadata properties that will allow it to know the endpoints it needs to complete the authorization flow.
63
64```json theme={null}
65{
66 "issuer": "https://auth.your-server.com",
67 "authorization_endpoint": "https://auth.your-server.com/authorize",
68 "token_endpoint": "https://auth.your-server.com/token",
69 "registration_endpoint": "https://auth.your-server.com/register"
70}
71```
72
73**4. Client Registration**
74
75With all the metadata out of the way, the client now needs to make sure that it's registered with the authorization server. This can be done in two ways.
76
77First, the client can be **pre-registered** with a given authorization server, in which case it can have embedded client registration information that it uses to complete the authorization flow.
78
79Alternatively, the client can use **Dynamic Client Registration** (DCR) to dynamically register itself with the authorization server. The latter scenario requires the authorization server to support DCR. If the authorization server does support DCR, the client will send a request to the `registration_endpoint` with its information:
80
81```json theme={null}
82{
83 "client_name": "My MCP Client",
84 "redirect_uris": ["http://localhost:3000/callback"],
85 "grant_types": ["authorization_code", "refresh_token"],
86 "response_types": ["code"]
87}
88```
89
90If the registration succeeds, the authorization server will return a JSON blob with client registration information.
91
92> [!TIP]
93>
94> **No DCR or Pre-Registration**
95>
96> In case an MCP client connects to an MCP server that doesn't use an authorization server that supports DCR and the client is not pre-registered with said authorization server, it's the responsibility of the client developer to provide an affordance for the end-user to enter client information manually.
97
98**5. User Authorization**
99
100The client will now need to open a browser to the `/authorize` endpoint, where the user can log in and grant the required permissions. The authorization server will then redirect back to the client with an authorization code that the client exchanges for tokens:
101
102```json theme={null}
103{
104 "access_token": "eyJhbGciOiJSUzI1NiIs...",
105 "refresh_token": "def502...",
106 "token_type": "Bearer",
107 "expires_in": 3600
108}
109```
110
111The access token is what the client will use to authenticate requests to the MCP server. This step follows standard [OAuth 2.1 authorization code with PKCE](https://oauth.net/2/grant-types/authorization-code/) conventions.
112
113**6. Making Authenticated Requests**
114
115Finally, the client can make requests to your MCP server using the access token embedded in the `Authorization` header:
116
117```http theme={null}
118GET /mcp HTTP/1.1
119Host: your-server.com
120Authorization: Bearer eyJhbGciOiJSUzI1NiIs...
121```
122
123The MCP server will need to validate the token and process the request if the token is valid and has the required permissions.
126124
127125## Implementation Example
128126
from line 138
140138
141139This command will pull the Keycloak container image locally and bootstrap the basic configuration. It will run on port `8080` and have an `admin` user with `admin` password.
142140
143<Warning>
144 **Not for Production**
145
146 The configuration above may be suitable for testing and experimentation; however, you should never use it in production. Refer to the [Configuring Keycloak for production](https://www.keycloak.org/server/configuration-production) guide for additional details on how to deploy the authorization server for scenarios that require reliability, security, and high availability.
147</Warning>
141> [!WARNING]
142>
143> **Not for Production**
144>
145> The configuration above may be suitable for testing and experimentation; however, you should never use it in production. Refer to the [Configuring Keycloak for production](https://www.keycloak.org/server/configuration-production) guide for additional details on how to deploy the authorization server for scenarios that require reliability, security, and high availability.
148146
149147You will be able to access the Keycloak authorization server from your browser at `http://localhost:8080`.
150148
151<Frame>
152 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-browser.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=cba689d986e113cbe937d732ac0558b6" alt="Keycloak admin dashboard authentication dialog." width="1834" height="1450" data-path="images/tutorial-authorization/keycloak-browser.png" />
153</Frame>
149
154150
155151When running with the default configuration, Keycloak will already support many of the capabilities that we need for MCP servers, including Dynamic Client Registration. You can check this by looking at the OIDC configuration, available at:
156152
from line 158
162158
163159Go to **Client scopes** in the Keycloak dashboard and create a new `mcp:tools` scope. We will use this to access all of the tools on our MCP server.
164160
165<Frame>
166 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-scopes.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=3cd49dc2e070027609ae495751e0db58" alt="Configuring Keycloak scopes." width="1999" height="1710" data-path="images/tutorial-authorization/keycloak-scopes.png" />
167</Frame>
161
168162
169163After creating the scope, make sure that you assign its type to **Default** and have flipped the **Include in token scope** switch, as this will be needed for token validation.
170164
from line 166
172166
173167To do this, open your `mcp:tools` client scope and click on **Mappers**, followed by **Configure a new mapper**. Select **Audience**.
174168
175<Frame>
176 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/scope-add-audience.gif?s=6ea9cf20c397f4c79c491c2e39019272" alt="Configuring an audience for a token in Keycloak." width="1080" height="921" data-path="images/tutorial-authorization/scope-add-audience.gif" />
177</Frame>
169
178170
179171For **Name**, use `audience-config`. Add a value for **Included Custom Audience**, set to `http://localhost:3000`. This will be the URI of our test server.
180172
181<Warning>
182 **Not for Production**
183
184 The audience configuration above is meant for testing. For production scenarios, additional set-up and configuration will be required to ensure that audiences are properly constrained for issued tokens. Specifically, the audience needs to be based on the resource parameter passed from the client, not a fixed value.
185</Warning>
173> [!WARNING]
174>
175> **Not for Production**
176>
177> The audience configuration above is meant for testing. For production scenarios, additional set-up and configuration will be required to ensure that audiences are properly constrained for issued tokens. Specifically, the audience needs to be based on the resource parameter passed from the client, not a fixed value.
186178
187179Now, navigate to **Clients**, then **Client registration**, and then **Trusted Hosts**. Disable the **Client URIs Must Match** setting and add the hosts from which you're testing. You can get your current host IP by running the `ifconfig` command on Linux or macOS, or `ipconfig` on Windows. You can see the IP address you need to add by looking at the keycloak logs for a line that looks like `Failed to verify remote host : 192.168.215.1`. Check that the IP address is associated with your host. This may be for a bridge network depending on your docker setup.
188180
189<Frame>
190 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-client.gif?s=b5d40b36a5f1ea1e818821bb8ea77f6b" alt="Setting up client registration details in Keycloak." width="1199" height="1027" data-path="images/tutorial-authorization/keycloak-client.gif" />
191</Frame>
192
193<Warning>
194 **Getting the Host**
195
196 If you are running Keycloak from a container, you will also be able to see the host IP from the Terminal in the container logs.
197</Warning>
181
182
183> [!WARNING]
184>
185> **Getting the Host**
186>
187> If you are running Keycloak from a container, you will also be able to see the host IP from the Terminal in the container logs.
198188
199189Lastly, we need to register a new client that we can use with the **MCP server itself** to talk to Keycloak for things like [token introspection](https://oauth.net/2/token-introspection/). To do that:
200190
from line 198
208198
209199When you open the client details, go to **Credentials** and take note of the **Client Secret**.
210200
211<Frame>
212 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-client-auth.gif?s=7152c41a5746994fd399024bc4659e40" alt="Creating a new client in Keycloak." width="1200" height="1023" data-path="images/tutorial-authorization/keycloak-client-auth.gif" />
213</Frame>
214
215<Warning>
216 **Handling Secrets**
217
218 Never embed client credentials directly in your code. We recommend using environment variables or specialized solutions for secret storage.
219</Warning>
201
202
203> [!WARNING]
204>
205> **Handling Secrets**
206>
207> Never embed client credentials directly in your code. We recommend using environment variables or specialized solutions for secret storage.
220208
221209With Keycloak configured, every time the authorization flow is triggered, your MCP server will receive a token like this:
222210
from line 234
246234}.[Signature]
247235```
248236
249<Warning>
250 **Embedded Audience**
251
252 Notice the `aud` claim embedded in the token - it's currently set to be the URI of the test MCP server and it's inferred from the scope that we've previously configured. This will be important in our implementation to validate.
253</Warning>
237> [!WARNING]
238>
239> **Embedded Audience**
240>
241> Notice the `aud` claim embedded in the token - it's currently set to be the URI of the test MCP server and it's inferred from the scope that we've previously configured. This will be important in our implementation to validate.
254242
255243### MCP Server Setup
256244
from line 246
258246
259247For our testing purposes, we will create an extremely simple MCP server that exposes two tools - one for addition and another for multiplication. The server will require authorization to access these.
260248
261<Tabs>
262 <Tab title="TypeScript">
263 You can see the complete TypeScript project in the [sample repository](https://github.com/localden/min-ts-mcp-auth).
264
265 Prior to running the code below, ensure that you have a `.env` file with the following content:
266
267 ```env theme={null}
268 # Server host/port
269 HOST=localhost
270 PORT=3000
271
272 # Auth server location
273 AUTH_HOST=localhost
274 AUTH_PORT=8080
275 AUTH_REALM=master
276
277 # Keycloak OAuth client credentials
278 OAUTH_CLIENT_ID=<YOUR_SERVER_CLIENT_ID>
279 OAUTH_CLIENT_SECRET=<YOUR_SERVER_CLIENT_SECRET>
280 ```
281
282 `OAUTH_CLIENT_ID` and `OAUTH_CLIENT_SECRET` are associated with the MCP server client we created earlier.
283
284 In addition to implementing the MCP authorization specification, the server below also does token introspection via Keycloak to make sure that the token it receives from the client is valid. It also implements basic logging to allow you to easily diagnose any issues.
285
286 ```typescript theme={null}
287 import "dotenv/config";
288 import express from "express";
289 import { randomUUID } from "node:crypto";
290 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
291 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
292 import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js";
293 import { z } from "zod";
294 import cors from "cors";
295 import {
296 mcpAuthMetadataRouter,
297 getOAuthProtectedResourceMetadataUrl,
298 } from "@modelcontextprotocol/sdk/server/auth/router.js";
299 import { requireBearerAuth } from "@modelcontextprotocol/sdk/server/auth/middleware/bearerAuth.js";
300 import { OAuthMetadata } from "@modelcontextprotocol/sdk/shared/auth.js";
301 import { checkResourceAllowed } from "@modelcontextprotocol/sdk/shared/auth-utils.js";
302 const CONFIG = {
303 host: process.env.HOST || "localhost",
304 port: Number(process.env.PORT) || 3000,
305 auth: {
306 host: process.env.AUTH_HOST || process.env.HOST || "localhost",
307 port: Number(process.env.AUTH_PORT) || 8080,
308 realm: process.env.AUTH_REALM || "master",
309 clientId: process.env.OAUTH_CLIENT_ID || "mcp-server",
310 clientSecret: process.env.OAUTH_CLIENT_SECRET || "",
311 },
312 };
313
314 function createOAuthUrls() {
315 const authBaseUrl = new URL(
316 `http://${CONFIG.auth.host}:${CONFIG.auth.port}/realms/${CONFIG.auth.realm}/`,
249**TypeScript**
250
251You can see the complete TypeScript project in the [sample repository](https://github.com/localden/min-ts-mcp-auth).
252
253Prior to running the code below, ensure that you have a `.env` file with the following content:
254
255```env theme={null}
256# Server host/port
257HOST=localhost
258PORT=3000
259
260# Auth server location
261AUTH_HOST=localhost
262AUTH_PORT=8080
263AUTH_REALM=master
264
265# Keycloak OAuth client credentials
266OAUTH_CLIENT_ID=<YOUR_SERVER_CLIENT_ID>
267OAUTH_CLIENT_SECRET=<YOUR_SERVER_CLIENT_SECRET>
268```
269
270`OAUTH_CLIENT_ID` and `OAUTH_CLIENT_SECRET` are associated with the MCP server client we created earlier.
271
272In addition to implementing the MCP authorization specification, the server below also does token introspection via Keycloak to make sure that the token it receives from the client is valid. It also implements basic logging to allow you to easily diagnose any issues.
273
274```typescript theme={null}
275import "dotenv/config";
276import express from "express";
277import { randomUUID } from "node:crypto";
278import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
279import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
280import { isInitializeRequest } from "@modelcontextprotocol/sdk/types.js";
281import { z } from "zod";
282import cors from "cors";
283import {
284 mcpAuthMetadataRouter,
285 getOAuthProtectedResourceMetadataUrl,
286} from "@modelcontextprotocol/sdk/server/auth/router.js";
287import { requireBearerAuth } from "@modelcontextprotocol/sdk/server/auth/middleware/bearerAuth.js";
288import { OAuthMetadata } from "@modelcontextprotocol/sdk/shared/auth.js";
289import { checkResourceAllowed } from "@modelcontextprotocol/sdk/shared/auth-utils.js";
290const CONFIG = {
291 host: process.env.HOST || "localhost",
292 port: Number(process.env.PORT) || 3000,
293 auth: {
294 host: process.env.AUTH_HOST || process.env.HOST || "localhost",
295 port: Number(process.env.AUTH_PORT) || 8080,
296 realm: process.env.AUTH_REALM || "master",
297 clientId: process.env.OAUTH_CLIENT_ID || "mcp-server",
298 clientSecret: process.env.OAUTH_CLIENT_SECRET || "",
299 },
300};
301
302function createOAuthUrls() {
303 const authBaseUrl = new URL(
304 `http://${CONFIG.auth.host}:${CONFIG.auth.port}/realms/${CONFIG.auth.realm}/`,
305 );
306 return {
307 issuer: authBaseUrl.toString(),
308 introspection_endpoint: new URL(
309 "protocol/openid-connect/token/introspect",
310 authBaseUrl,
311 ).toString(),
312 authorization_endpoint: new URL(
313 "protocol/openid-connect/auth",
314 authBaseUrl,
315 ).toString(),
316 token_endpoint: new URL(
317 "protocol/openid-connect/token",
318 authBaseUrl,
319 ).toString(),
320 };
321}
322
323function createRequestLogger() {
324 return (req: any, res: any, next: any) => {
325 const start = Date.now();
326 res.on("finish", () => {
327 const ms = Date.now() - start;
328 console.log(
329 `${req.method} ${req.originalUrl} -> ${res.statusCode} ${ms}ms`,
317330 );
318 return {
319 issuer: authBaseUrl.toString(),
320 introspection_endpoint: new URL(
321 "protocol/openid-connect/token/introspect",
322 authBaseUrl,
323 ).toString(),
324 authorization_endpoint: new URL(
325 "protocol/openid-connect/auth",
326 authBaseUrl,
327 ).toString(),
328 token_endpoint: new URL(
329 "protocol/openid-connect/token",
330 authBaseUrl,
331 ).toString(),
332 };
331 });
332 next();
333 };
334}
335
336const app = express();
337
338app.use(
339 express.json({
340 verify: (req: any, _res, buf) => {
341 req.rawBody = buf?.toString() ?? "";
342 },
343 }),
344);
345
346app.use(
347 cors({
348 origin: "*",
349 exposedHeaders: ["Mcp-Session-Id"],
350 }),
351);
352
353app.use(createRequestLogger());
354
355const mcpServerUrl = new URL(`http://${CONFIG.host}:${CONFIG.port}`);
356const oauthUrls = createOAuthUrls();
357
358const oauthMetadata: OAuthMetadata = {
359 ...oauthUrls,
360 response_types_supported: ["code"],
361};
362
363const tokenVerifier = {
364 verifyAccessToken: async (token: string) => {
365 const endpoint = oauthMetadata.introspection_endpoint;
366
367 if (!endpoint) {
368 console.error("[auth] no introspection endpoint in metadata");
369 throw new Error("No token verification endpoint available in metadata");
333370 }
334371
335 function createRequestLogger() {
336 return (req: any, res: any, next: any) => {
337 const start = Date.now();
338 res.on("finish", () => {
339 const ms = Date.now() - start;
340 console.log(
341 `${req.method} ${req.originalUrl} -> ${res.statusCode} ${ms}ms`,
342 );
343 });
344 next();
345 };
372 const params = new URLSearchParams({
373 token: token,
374 client_id: CONFIG.auth.clientId,
375 });
376
377 if (CONFIG.auth.clientSecret) {
378 params.set("client_secret", CONFIG.auth.clientSecret);
346379 }
347380
348 const app = express();
349
350 app.use(
351 express.json({
352 verify: (req: any, _res, buf) => {
353 req.rawBody = buf?.toString() ?? "";
381 let response: Response;
382 try {
383 response = await fetch(endpoint, {
384 method: "POST",
385 headers: {
386 "Content-Type": "application/x-www-form-urlencoded",
354387 },
388 body: params.toString(),
389 });
390 } catch (e) {
391 console.error("[auth] introspection fetch threw", e);
392 throw e;
393 }
394
395 if (!response.ok) {
396 const txt = await response.text();
397 console.error("[auth] introspection non-OK", { status: response.status });
398
399 try {
400 const obj = JSON.parse(txt);
401 console.log(JSON.stringify(obj, null, 2));
402 } catch {
403 console.error(txt);
404 }
405 throw new Error(`Invalid or expired token: ${txt}`);
406 }
407
408 let data: any;
409 try {
410 data = await response.json();
411 } catch (e) {
412 const txt = await response.text();
413 console.error("[auth] failed to parse introspection JSON", {
414 error: String(e),
415 body: txt,
416 });
417 throw e;
418 }
419
420 if (data.active === false) {
421 throw new Error("Inactive token");
422 }
423
424 if (!data.aud) {
425 throw new Error("Resource indicator (aud) missing");
426 }
427
428 const audiences: string[] = Array.isArray(data.aud) ? data.aud : [data.aud];
429 const allowed = audiences.some((a) =>
430 checkResourceAllowed({
431 requestedResource: a,
432 configuredResource: mcpServerUrl,
355433 }),
356434 );
357
358 app.use(
359 cors({
360 origin: "*",
361 exposedHeaders: ["Mcp-Session-Id"],
362 }),
363 );
364
365 app.use(createRequestLogger());
366
367 const mcpServerUrl = new URL(`http://${CONFIG.host}:${CONFIG.port}`);
368 const oauthUrls = createOAuthUrls();
369
370 const oauthMetadata: OAuthMetadata = {
371 ...oauthUrls,
372 response_types_supported: ["code"],
435 if (!allowed) {
436 throw new Error(
437 `None of the provided audiences are allowed. Expected ${mcpServerUrl}, got: ${audiences.join(", ")}`,
438 );
439 }
440
441 return {
442 token,
443 clientId: data.client_id,
444 scopes: data.scope ? data.scope.split(" ") : [],
445 expiresAt: data.exp,
373446 };
374
375 const tokenVerifier = {
376 verifyAccessToken: async (token: string) => {
377 const endpoint = oauthMetadata.introspection_endpoint;
378
379 if (!endpoint) {
380 console.error("[auth] no introspection endpoint in metadata");
381 throw new Error("No token verification endpoint available in metadata");
447 },
448};
449app.use(
450 mcpAuthMetadataRouter({
451 oauthMetadata,
452 resourceServerUrl: mcpServerUrl,
453 scopesSupported: ["mcp:tools"],
454 resourceName: "MCP Demo Server",
455 }),
456);
457
458const authMiddleware = requireBearerAuth({
459 verifier: tokenVerifier,
460 requiredScopes: [],
461 resourceMetadataUrl: getOAuthProtectedResourceMetadataUrl(mcpServerUrl),
462});
463
464const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {};
465
466function createMcpServer() {
467 const server = new McpServer({
468 name: "example-server",
469 version: "1.0.0",
470 });
471
472 server.registerTool(
473 "add",
474 {
475 title: "Addition Tool",
476 description: "Add two numbers together",
477 inputSchema: {
478 a: z.number().describe("First number to add"),
479 b: z.number().describe("Second number to add"),
480 },
481 },
482 async ({ a, b }) => ({
483 content: [{ type: "text", text: `${a} + ${b} = ${a + b}` }],
484 }),
485 );
486
487 server.registerTool(
488 "multiply",
489 {
490 title: "Multiplication Tool",
491 description: "Multiply two numbers together",
492 inputSchema: {
493 x: z.number().describe("First number to multiply"),
494 y: z.number().describe("Second number to multiply"),
495 },
496 },
497 async ({ x, y }) => ({
498 content: [{ type: "text", text: `${x} × ${y} = ${x * y}` }],
499 }),
500 );
501
502 return server;
503}
504
505const mcpPostHandler = async (req: express.Request, res: express.Response) => {
506 const sessionId = req.headers["mcp-session-id"] as string | undefined;
507 let transport: StreamableHTTPServerTransport;
508
509 if (sessionId && transports[sessionId]) {
510 transport = transports[sessionId];
511 } else if (!sessionId && isInitializeRequest(req.body)) {
512 transport = new StreamableHTTPServerTransport({
513 sessionIdGenerator: () => randomUUID(),
514 onsessioninitialized: (sessionId) => {
515 transports[sessionId] = transport;
516 },
517 });
518
519 transport.onclose = () => {
520 if (transport.sessionId) {
521 delete transports[transport.sessionId];
522 }
523 };
524
525 const server = createMcpServer();
526 await server.connect(transport);
527 } else {
528 res.status(400).json({
529 jsonrpc: "2.0",
530 error: {
531 code: -32000,
532 message: "Bad Request: No valid session ID provided",
533 },
534 id: null,
535 });
536 return;
537 }
538
539 await transport.handleRequest(req, res, req.body);
540};
541
542const handleSessionRequest = async (
543 req: express.Request,
544 res: express.Response,
545) => {
546 const sessionId = req.headers["mcp-session-id"] as string | undefined;
547 if (!sessionId || !transports[sessionId]) {
548 res.status(400).send("Invalid or missing session ID");
549 return;
550 }
551
552 const transport = transports[sessionId];
553 await transport.handleRequest(req, res);
554};
555
556app.post("/", authMiddleware, mcpPostHandler);
557app.get("/", authMiddleware, handleSessionRequest);
558app.delete("/", authMiddleware, handleSessionRequest);
559
560app.listen(CONFIG.port, CONFIG.host, () => {
561 console.log(`🚀 MCP Server running on ${mcpServerUrl.origin}`);
562 console.log(`📡 MCP endpoint available at ${mcpServerUrl.origin}`);
563 console.log(
564 `🔐 OAuth metadata available at ${getOAuthProtectedResourceMetadataUrl(mcpServerUrl)}`,
565 );
566});
567```
568
569When you run the server, you can add it to your MCP client, such as Visual Studio Code, by providing the MCP server endpoint.
570
571For more details about implementing MCP servers in TypeScript, refer to the [TypeScript SDK documentation](https://github.com/modelcontextprotocol/typescript-sdk).
572
573**Python**
574
575You can see the complete Python project in the [sample repository](https://github.com/modelcontextprotocol/python-sdk/tree/main/examples/servers/simple-auth).
576
577To simplify our authorization interaction, in Python scenarios we rely on [FastMCP](https://gofastmcp.com/getting-started/welcome). Many of the conventions around authorization, like the endpoints and token validation logic, are consistent across languages, but some offer simpler ways of integrating them in production scenarios.
578
579Prior to writing the actual server, we need to set up our configuration in `config.py` - the contents are entirely based on your local server setup:
580
581```python theme={null}
582"""Configuration settings for the MCP auth server."""
583
584import os
585from typing import Optional
586
587
588class Config:
589 """Configuration class that loads from environment variables with sensible defaults."""
590
591 # Server settings
592 HOST: str = os.getenv("HOST", "localhost")
593 PORT: int = int(os.getenv("PORT", "3000"))
594
595 # Auth server settings
596 AUTH_HOST: str = os.getenv("AUTH_HOST", "localhost")
597 AUTH_PORT: int = int(os.getenv("AUTH_PORT", "8080"))
598 AUTH_REALM: str = os.getenv("AUTH_REALM", "master")
599
600 # OAuth client settings
601 OAUTH_CLIENT_ID: str = os.getenv("OAUTH_CLIENT_ID", "mcp-server")
602 OAUTH_CLIENT_SECRET: str = os.getenv("OAUTH_CLIENT_SECRET", "UO3rmozkFFkXr0QxPTkzZ0LMXDidIikB")
603
604 # Server settings
605 MCP_SCOPE: str = os.getenv("MCP_SCOPE", "mcp:tools")
606 OAUTH_STRICT: bool = os.getenv("OAUTH_STRICT", "false").lower() in ("true", "1", "yes")
607 TRANSPORT: str = os.getenv("TRANSPORT", "streamable-http")
608
609 @property
610 def server_url(self) -> str:
611 """Build the server URL."""
612 return f"http://{self.HOST}:{self.PORT}"
613
614 @property
615 def auth_base_url(self) -> str:
616 """Build the auth server base URL."""
617 return f"http://{self.AUTH_HOST}:{self.AUTH_PORT}/realms/{self.AUTH_REALM}/"
618
619 def validate(self) -> None:
620 """Validate configuration."""
621 if self.TRANSPORT not in ["sse", "streamable-http"]:
622 raise ValueError(f"Invalid transport: {self.TRANSPORT}. Must be 'sse' or 'streamable-http'")
623
624
625# Global configuration instance
626config = Config()
627
628```
629
630The server implementation is as follows:
631
632```python theme={null}
633import datetime
634import logging
635from typing import Any
636
637from pydantic import AnyHttpUrl
638
639from mcp.server.auth.settings import AuthSettings
640from mcp.server.fastmcp.server import FastMCP
641
642from .config import config
643from .token_verifier import IntrospectionTokenVerifier
644
645logger = logging.getLogger(__name__)
646
647
648def create_oauth_urls() -> dict[str, str]:
649 """Create OAuth URLs based on configuration (Keycloak-style)."""
650 from urllib.parse import urljoin
651
652 auth_base_url = config.auth_base_url
653
654 return {
655 "issuer": auth_base_url,
656 "introspection_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token/introspect"),
657 "authorization_endpoint": urljoin(auth_base_url, "protocol/openid-connect/auth"),
658 "token_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token"),
659 }
660
661
662def create_server() -> FastMCP:
663 """Create and configure the FastMCP server."""
664
665 config.validate()
666
667 oauth_urls = create_oauth_urls()
668
669 token_verifier = IntrospectionTokenVerifier(
670 introspection_endpoint=oauth_urls["introspection_endpoint"],
671 server_url=config.server_url,
672 client_id=config.OAUTH_CLIENT_ID,
673 client_secret=config.OAUTH_CLIENT_SECRET,
674 )
675
676 app = FastMCP(
677 name="MCP Resource Server",
678 instructions="Resource Server that validates tokens via Authorization Server introspection",
679 host=config.HOST,
680 port=config.PORT,
681 debug=True,
682 streamable_http_path="/",
683 token_verifier=token_verifier,
684 auth=AuthSettings(
685 issuer_url=AnyHttpUrl(oauth_urls["issuer"]),
686 required_scopes=[config.MCP_SCOPE],
687 resource_server_url=AnyHttpUrl(config.server_url),
688 ),
689 )
690
691 @app.tool()
692 async def add_numbers(a: float, b: float) -> dict[str, Any]:
693 """
694 Add two numbers together.
695 This tool demonstrates basic arithmetic operations with OAuth authentication.
696
697 Args:
698 a: The first number to add
699 b: The second number to add
700 """
701 result = a + b
702 return {
703 "operation": "addition",
704 "operand_a": a,
705 "operand_b": b,
706 "result": result,
707 "timestamp": datetime.datetime.now().isoformat()
382708 }
383709
384 const params = new URLSearchParams({
385 token: token,
386 client_id: CONFIG.auth.clientId,
387 });
388
389 if (CONFIG.auth.clientSecret) {
390 params.set("client_secret", CONFIG.auth.clientSecret);
710 @app.tool()
711 async def multiply_numbers(x: float, y: float) -> dict[str, Any]:
712 """
713 Multiply two numbers together.
714 This tool demonstrates basic arithmetic operations with OAuth authentication.
715
716 Args:
717 x: The first number to multiply
718 y: The second number to multiply
719 """
720 result = x * y
721 return {
722 "operation": "multiplication",
723 "operand_x": x,
724 "operand_y": y,
725 "result": result,
726 "timestamp": datetime.datetime.now().isoformat()
391727 }
392728
393 let response: Response;
394 try {
395 response = await fetch(endpoint, {
396 method: "POST",
397 headers: {
398 "Content-Type": "application/x-www-form-urlencoded",
399 },
400 body: params.toString(),
401 });
402 } catch (e) {
403 console.error("[auth] introspection fetch threw", e);
404 throw e;
729 return app
730
731
732def main() -> int:
733 """
734 Run the MCP Resource Server.
735
736 This server:
737 - Provides RFC 9728 Protected Resource Metadata
738 - Validates tokens via Authorization Server introspection
739 - Serves MCP tools requiring authentication
740
741 Configuration is loaded from config.py and environment variables.
742 """
743 logging.basicConfig(level=logging.INFO)
744
745 try:
746 config.validate()
747 oauth_urls = create_oauth_urls()
748
749 except ValueError as e:
750 logger.error("Configuration error: %s", e)
751 return 1
752
753 try:
754 mcp_server = create_server()
755
756 logger.info("Starting MCP Server on %s:%s", config.HOST, config.PORT)
757 logger.info("Authorization Server: %s", oauth_urls["issuer"])
758 logger.info("Transport: %s", config.TRANSPORT)
759
760 mcp_server.run(transport=config.TRANSPORT)
761 return 0
762
763 except Exception:
764 logger.exception("Server error")
765 return 1
766
767
768if __name__ == "__main__":
769 exit(main())
770```
771
772Lastly, the token verification logic is delegated entirely to `token_verifier.py`, ensuring that we can use the Keycloak introspection endpoint to verify the validity of any credential artifacts
773
774```python theme={null}
775"""Token verifier implementation using OAuth 2.0 Token Introspection (RFC 7662)."""
776
777import logging
778from typing import Any
779
780from mcp.server.auth.provider import AccessToken, TokenVerifier
781from mcp.shared.auth_utils import check_resource_allowed, resource_url_from_server_url
782
783logger = logging.getLogger(__name__)
784
785
786class IntrospectionTokenVerifier(TokenVerifier):
787 """Token verifier that uses OAuth 2.0 Token Introspection (RFC 7662).
788 """
789
790 def __init__(
791 self,
792 introspection_endpoint: str,
793 server_url: str,
794 client_id: str,
795 client_secret: str,
796 ):
797 self.introspection_endpoint = introspection_endpoint
798 self.server_url = server_url
799 self.client_id = client_id
800 self.client_secret = client_secret
801 self.resource_url = resource_url_from_server_url(server_url)
802
803 async def verify_token(self, token: str) -> AccessToken | None:
804 """Verify token via introspection endpoint."""
805 import httpx
806
807 if not self.introspection_endpoint.startswith(("https://", "http://localhost", "http://127.0.0.1")):
808 return None
809
810 timeout = httpx.Timeout(10.0, connect=5.0)
811 limits = httpx.Limits(max_connections=10, max_keepalive_connections=5)
812
813 async with httpx.AsyncClient(
814 timeout=timeout,
815 limits=limits,
816 verify=True,
817 ) as client:
818 try:
819 form_data = {
820 "token": token,
821 "client_id": self.client_id,
822 "client_secret": self.client_secret,
823 }
824 headers = {"Content-Type": "application/x-www-form-urlencoded"}
825
826 response = await client.post(
827 self.introspection_endpoint,
828 data=form_data,
829 headers=headers,
830 )
831
832 if response.status_code != 200:
833 return None
834
835 data = response.json()
836 if not data.get("active", False):
837 return None
838
839 if not self._validate_resource(data):
840 return None
841
842 return AccessToken(
843 token=token,
844 client_id=data.get("client_id", "unknown"),
845 scopes=data.get("scope", "").split() if data.get("scope") else [],
846 expires_at=data.get("exp"),
847 resource=data.get("aud"), # Include resource in token
848 )
849
850 except Exception as e:
851 return None
852
853 def _validate_resource(self, token_data: dict[str, Any]) -> bool:
854 """Validate token was issued for this resource server.
855
856 Rules:
857 - Reject if 'aud' missing.
858 - Accept if any audience entry matches the derived resource URL.
859 - Supports string or list forms per JWT spec.
860 """
861 if not self.server_url or not self.resource_url:
862 return False
863
864 aud: list[str] | str | None = token_data.get("aud")
865 if isinstance(aud, list):
866 return any(self._is_valid_resource(a) for a in aud)
867 if isinstance(aud, str):
868 return self._is_valid_resource(aud)
869 return False
870
871 def _is_valid_resource(self, resource: str) -> bool:
872 """Check if the given resource matches our server."""
873 return check_resource_allowed(self.resource_url, resource)
874```
875
876For more details, see the [Python SDK documentation](https://github.com/modelcontextprotocol/python-sdk).
877
878**C#**
879
880You can see the complete C# project in the [sample repository](https://github.com/localden/min-cs-mcp-auth).
881
882To set up authorization in your MCP server using the MCP C# SDK, you can lean on the standard ASP.NET Core builder pattern. Instead of using the introspection endpoint provided by Keycloak, we will use built-in ASP.NET Core capabilities for token validation.
883
884```csharp theme={null}
885using Microsoft.AspNetCore.Authentication.JwtBearer;
886using Microsoft.IdentityModel.Tokens;
887using ModelContextProtocol.AspNetCore.Authentication;
888using ProtectedMcpServer.Tools;
889using System.Security.Claims;
890
891var builder = WebApplication.CreateBuilder(args);
892
893var serverUrl = "http://localhost:3000/";
894var authorizationServerUrl = "http://localhost:8080/realms/master/";
895
896builder.Services.AddAuthentication(options =>
897{
898 options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
899 options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
900})
901.AddJwtBearer(options =>
902{
903 options.Authority = authorizationServerUrl;
904 var normalizedServerAudience = serverUrl.TrimEnd('/');
905 options.TokenValidationParameters = new TokenValidationParameters
906 {
907 ValidIssuer = authorizationServerUrl,
908 ValidAudiences = new[] { normalizedServerAudience, serverUrl },
909 AudienceValidator = (audiences, securityToken, validationParameters) =>
910 {
911 if (audiences == null) return false;
912 foreach (var aud in audiences)
913 {
914 if (string.Equals(aud.TrimEnd('/'), normalizedServerAudience, StringComparison.OrdinalIgnoreCase))
915 {
916 return true;
917 }
918 }
919 return false;
405920 }
406
407 if (!response.ok) {
408 const txt = await response.text();
409 console.error("[auth] introspection non-OK", { status: response.status });
410
411 try {
412 const obj = JSON.parse(txt);
413 console.log(JSON.stringify(obj, null, 2));
414 } catch {
415 console.error(txt);
416 }
417 throw new Error(`Invalid or expired token: ${txt}`);
418 }
419
420 let data: any;
421 try {
422 data = await response.json();
423 } catch (e) {
424 const txt = await response.text();
425 console.error("[auth] failed to parse introspection JSON", {
426 error: String(e),
427 body: txt,
428 });
429 throw e;
430 }
431
432 if (data.active === false) {
433 throw new Error("Inactive token");
434 }
435
436 if (!data.aud) {
437 throw new Error("Resource indicator (aud) missing");
438 }
439
440 const audiences: string[] = Array.isArray(data.aud) ? data.aud : [data.aud];
441 const allowed = audiences.some((a) =>
442 checkResourceAllowed({
443 requestedResource: a,
444 configuredResource: mcpServerUrl,
445 }),
446 );
447 if (!allowed) {
448 throw new Error(
449 `None of the provided audiences are allowed. Expected ${mcpServerUrl}, got: ${audiences.join(", ")}`,
450 );
451 }
452
453 return {
454 token,
455 clientId: data.client_id,
456 scopes: data.scope ? data.scope.split(" ") : [],
457 expiresAt: data.exp,
458 };
459 },
460921 };
461 app.use(
462 mcpAuthMetadataRouter({
463 oauthMetadata,
464 resourceServerUrl: mcpServerUrl,
465 scopesSupported: ["mcp:tools"],
466 resourceName: "MCP Demo Server",
467 }),
468 );
469
470 const authMiddleware = requireBearerAuth({
471 verifier: tokenVerifier,
472 requiredScopes: [],
473 resourceMetadataUrl: getOAuthProtectedResourceMetadataUrl(mcpServerUrl),
474 });
475
476 const transports: { [sessionId: string]: StreamableHTTPServerTransport } = {};
477
478 function createMcpServer() {
479 const server = new McpServer({
480 name: "example-server",
481 version: "1.0.0",
482 });
483
484 server.registerTool(
485 "add",
922
923 options.RequireHttpsMetadata = false; // Set to true in production
924
925 options.Events = new JwtBearerEvents
926 {
927 OnTokenValidated = context =>
486928 {
487 title: "Addition Tool",
488 description: "Add two numbers together",
489 inputSchema: {
490 a: z.number().describe("First number to add"),
491 b: z.number().describe("Second number to add"),
492 },
929 var name = context.Principal?.Identity?.Name ?? "unknown";
930 var email = context.Principal?.FindFirstValue("preferred_username") ?? "unknown";
931 Console.WriteLine($"Token validated for: {name} ({email})");
932 return Task.CompletedTask;
493933 },
494 async ({ a, b }) => ({
495 content: [{ type: "text", text: `${a} + ${b} = ${a + b}` }],
496 }),
497 );
498
499 server.registerTool(
500 "multiply",
934 OnAuthenticationFailed = context =>
501935 {
502 title: "Multiplication Tool",
503 description: "Multiply two numbers together",
504 inputSchema: {
505 x: z.number().describe("First number to multiply"),
506 y: z.number().describe("Second number to multiply"),
507 },
936 Console.WriteLine($"Authentication failed: {context.Exception.Message}");
937 return Task.CompletedTask;
508938 },
509 async ({ x, y }) => ({
510 content: [{ type: "text", text: `${x} × ${y} = ${x * y}` }],
511 }),
512 );
513
514 return server;
515 }
516
517 const mcpPostHandler = async (req: express.Request, res: express.Response) => {
518 const sessionId = req.headers["mcp-session-id"] as string | undefined;
519 let transport: StreamableHTTPServerTransport;
520
521 if (sessionId && transports[sessionId]) {
522 transport = transports[sessionId];
523 } else if (!sessionId && isInitializeRequest(req.body)) {
524 transport = new StreamableHTTPServerTransport({
525 sessionIdGenerator: () => randomUUID(),
526 onsessioninitialized: (sessionId) => {
527 transports[sessionId] = transport;
528 },
529 });
530
531 transport.onclose = () => {
532 if (transport.sessionId) {
533 delete transports[transport.sessionId];
534 }
535 };
536
537 const server = createMcpServer();
538 await server.connect(transport);
539 } else {
540 res.status(400).json({
541 jsonrpc: "2.0",
542 error: {
543 code: -32000,
544 message: "Bad Request: No valid session ID provided",
545 },
546 id: null,
547 });
548 return;
549 }
550
551 await transport.handleRequest(req, res, req.body);
552939 };
553
554 const handleSessionRequest = async (
555 req: express.Request,
556 res: express.Response,
557 ) => {
558 const sessionId = req.headers["mcp-session-id"] as string | undefined;
559 if (!sessionId || !transports[sessionId]) {
560 res.status(400).send("Invalid or missing session ID");
561 return;
562 }
563
564 const transport = transports[sessionId];
565 await transport.handleRequest(req, res);
940})
941.AddMcp(options =>
942{
943 options.ResourceMetadata = new()
944 {
945 Resource = new Uri(serverUrl),
946 ResourceDocumentation = new Uri("https://docs.example.com/api/math"),
947 AuthorizationServers = { new Uri(authorizationServerUrl) },
948 ScopesSupported = ["mcp:tools"]
566949 };
567
568 app.post("/", authMiddleware, mcpPostHandler);
569 app.get("/", authMiddleware, handleSessionRequest);
570 app.delete("/", authMiddleware, handleSessionRequest);
571
572 app.listen(CONFIG.port, CONFIG.host, () => {
573 console.log(`🚀 MCP Server running on ${mcpServerUrl.origin}`);
574 console.log(`📡 MCP endpoint available at ${mcpServerUrl.origin}`);
575 console.log(
576 `🔐 OAuth metadata available at ${getOAuthProtectedResourceMetadataUrl(mcpServerUrl)}`,
577 );
578 });
579 ```
580
581 When you run the server, you can add it to your MCP client, such as Visual Studio Code, by providing the MCP server endpoint.
582
583 For more details about implementing MCP servers in TypeScript, refer to the [TypeScript SDK documentation](https://github.com/modelcontextprotocol/typescript-sdk).
584 </Tab>
585
586 <Tab title="Python">
587 You can see the complete Python project in the [sample repository](https://github.com/modelcontextprotocol/python-sdk/tree/main/examples/servers/simple-auth).
588
589 To simplify our authorization interaction, in Python scenarios we rely on [FastMCP](https://gofastmcp.com/getting-started/welcome). Many of the conventions around authorization, like the endpoints and token validation logic, are consistent across languages, but some offer simpler ways of integrating them in production scenarios.
590
591 Prior to writing the actual server, we need to set up our configuration in `config.py` - the contents are entirely based on your local server setup:
592
593 ```python theme={null}
594 """Configuration settings for the MCP auth server."""
595
596 import os
597 from typing import Optional
598
599
600 class Config:
601 """Configuration class that loads from environment variables with sensible defaults."""
602
603 # Server settings
604 HOST: str = os.getenv("HOST", "localhost")
605 PORT: int = int(os.getenv("PORT", "3000"))
606
607 # Auth server settings
608 AUTH_HOST: str = os.getenv("AUTH_HOST", "localhost")
609 AUTH_PORT: int = int(os.getenv("AUTH_PORT", "8080"))
610 AUTH_REALM: str = os.getenv("AUTH_REALM", "master")
611
612 # OAuth client settings
613 OAUTH_CLIENT_ID: str = os.getenv("OAUTH_CLIENT_ID", "mcp-server")
614 OAUTH_CLIENT_SECRET: str = os.getenv("OAUTH_CLIENT_SECRET", "UO3rmozkFFkXr0QxPTkzZ0LMXDidIikB")
615
616 # Server settings
617 MCP_SCOPE: str = os.getenv("MCP_SCOPE", "mcp:tools")
618 OAUTH_STRICT: bool = os.getenv("OAUTH_STRICT", "false").lower() in ("true", "1", "yes")
619 TRANSPORT: str = os.getenv("TRANSPORT", "streamable-http")
620
621 @property
622 def server_url(self) -> str:
623 """Build the server URL."""
624 return f"http://{self.HOST}:{self.PORT}"
625
626 @property
627 def auth_base_url(self) -> str:
628 """Build the auth server base URL."""
629 return f"http://{self.AUTH_HOST}:{self.AUTH_PORT}/realms/{self.AUTH_REALM}/"
630
631 def validate(self) -> None:
632 """Validate configuration."""
633 if self.TRANSPORT not in ["sse", "streamable-http"]:
634 raise ValueError(f"Invalid transport: {self.TRANSPORT}. Must be 'sse' or 'streamable-http'")
635
636
637 # Global configuration instance
638 config = Config()
639
640 ```
641
642 The server implementation is as follows:
643
644 ```python theme={null}
645 import datetime
646 import logging
647 from typing import Any
648
649 from pydantic import AnyHttpUrl
650
651 from mcp.server.auth.settings import AuthSettings
652 from mcp.server.fastmcp.server import FastMCP
653
654 from .config import config
655 from .token_verifier import IntrospectionTokenVerifier
656
657 logger = logging.getLogger(__name__)
658
659
660 def create_oauth_urls() -> dict[str, str]:
661 """Create OAuth URLs based on configuration (Keycloak-style)."""
662 from urllib.parse import urljoin
663
664 auth_base_url = config.auth_base_url
665
666 return {
667 "issuer": auth_base_url,
668 "introspection_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token/introspect"),
669 "authorization_endpoint": urljoin(auth_base_url, "protocol/openid-connect/auth"),
670 "token_endpoint": urljoin(auth_base_url, "protocol/openid-connect/token"),
671 }
672
673
674 def create_server() -> FastMCP:
675 """Create and configure the FastMCP server."""
676
677 config.validate()
678
679 oauth_urls = create_oauth_urls()
680
681 token_verifier = IntrospectionTokenVerifier(
682 introspection_endpoint=oauth_urls["introspection_endpoint"],
683 server_url=config.server_url,
684 client_id=config.OAUTH_CLIENT_ID,
685 client_secret=config.OAUTH_CLIENT_SECRET,
686 )
687
688 app = FastMCP(
689 name="MCP Resource Server",
690 instructions="Resource Server that validates tokens via Authorization Server introspection",
691 host=config.HOST,
692 port=config.PORT,
693 debug=True,
694 streamable_http_path="/",
695 token_verifier=token_verifier,
696 auth=AuthSettings(
697 issuer_url=AnyHttpUrl(oauth_urls["issuer"]),
698 required_scopes=[config.MCP_SCOPE],
699 resource_server_url=AnyHttpUrl(config.server_url),
700 ),
701 )
702
703 @app.tool()
704 async def add_numbers(a: float, b: float) -> dict[str, Any]:
705 """
706 Add two numbers together.
707 This tool demonstrates basic arithmetic operations with OAuth authentication.
708
709 Args:
710 a: The first number to add
711 b: The second number to add
712 """
713 result = a + b
714 return {
715 "operation": "addition",
716 "operand_a": a,
717 "operand_b": b,
718 "result": result,
719 "timestamp": datetime.datetime.now().isoformat()
720 }
721
722 @app.tool()
723 async def multiply_numbers(x: float, y: float) -> dict[str, Any]:
724 """
725 Multiply two numbers together.
726 This tool demonstrates basic arithmetic operations with OAuth authentication.
727
728 Args:
729 x: The first number to multiply
730 y: The second number to multiply
731 """
732 result = x * y
733 return {
734 "operation": "multiplication",
735 "operand_x": x,
736 "operand_y": y,
737 "result": result,
738 "timestamp": datetime.datetime.now().isoformat()
739 }
740
741 return app
742
743
744 def main() -> int:
745 """
746 Run the MCP Resource Server.
747
748 This server:
749 - Provides RFC 9728 Protected Resource Metadata
750 - Validates tokens via Authorization Server introspection
751 - Serves MCP tools requiring authentication
752
753 Configuration is loaded from config.py and environment variables.
754 """
755 logging.basicConfig(level=logging.INFO)
756
757 try:
758 config.validate()
759 oauth_urls = create_oauth_urls()
760
761 except ValueError as e:
762 logger.error("Configuration error: %s", e)
763 return 1
764
765 try:
766 mcp_server = create_server()
767
768 logger.info("Starting MCP Server on %s:%s", config.HOST, config.PORT)
769 logger.info("Authorization Server: %s", oauth_urls["issuer"])
770 logger.info("Transport: %s", config.TRANSPORT)
771
772 mcp_server.run(transport=config.TRANSPORT)
773 return 0
774
775 except Exception:
776 logger.exception("Server error")
777 return 1
778
779
780 if __name__ == "__main__":
781 exit(main())
782 ```
783
784 Lastly, the token verification logic is delegated entirely to `token_verifier.py`, ensuring that we can use the Keycloak introspection endpoint to verify the validity of any credential artifacts
785
786 ```python theme={null}
787 """Token verifier implementation using OAuth 2.0 Token Introspection (RFC 7662)."""
788
789 import logging
790 from typing import Any
791
792 from mcp.server.auth.provider import AccessToken, TokenVerifier
793 from mcp.shared.auth_utils import check_resource_allowed, resource_url_from_server_url
794
795 logger = logging.getLogger(__name__)
796
797
798 class IntrospectionTokenVerifier(TokenVerifier):
799 """Token verifier that uses OAuth 2.0 Token Introspection (RFC 7662).
800 """
801
802 def __init__(
803 self,
804 introspection_endpoint: str,
805 server_url: str,
806 client_id: str,
807 client_secret: str,
808 ):
809 self.introspection_endpoint = introspection_endpoint
810 self.server_url = server_url
811 self.client_id = client_id
812 self.client_secret = client_secret
813 self.resource_url = resource_url_from_server_url(server_url)
814
815 async def verify_token(self, token: str) -> AccessToken | None:
816 """Verify token via introspection endpoint."""
817 import httpx
818
819 if not self.introspection_endpoint.startswith(("https://", "http://localhost", "http://127.0.0.1")):
820 return None
821
822 timeout = httpx.Timeout(10.0, connect=5.0)
823 limits = httpx.Limits(max_connections=10, max_keepalive_connections=5)
824
825 async with httpx.AsyncClient(
826 timeout=timeout,
827 limits=limits,
828 verify=True,
829 ) as client:
830 try:
831 form_data = {
832 "token": token,
833 "client_id": self.client_id,
834 "client_secret": self.client_secret,
835 }
836 headers = {"Content-Type": "application/x-www-form-urlencoded"}
837
838 response = await client.post(
839 self.introspection_endpoint,
840 data=form_data,
841 headers=headers,
842 )
843
844 if response.status_code != 200:
845 return None
846
847 data = response.json()
848 if not data.get("active", False):
849 return None
850
851 if not self._validate_resource(data):
852 return None
853
854 return AccessToken(
855 token=token,
856 client_id=data.get("client_id", "unknown"),
857 scopes=data.get("scope", "").split() if data.get("scope") else [],
858 expires_at=data.get("exp"),
859 resource=data.get("aud"), # Include resource in token
860 )
861
862 except Exception as e:
863 return None
864
865 def _validate_resource(self, token_data: dict[str, Any]) -> bool:
866 """Validate token was issued for this resource server.
867
868 Rules:
869 - Reject if 'aud' missing.
870 - Accept if any audience entry matches the derived resource URL.
871 - Supports string or list forms per JWT spec.
872 """
873 if not self.server_url or not self.resource_url:
874 return False
875
876 aud: list[str] | str | None = token_data.get("aud")
877 if isinstance(aud, list):
878 return any(self._is_valid_resource(a) for a in aud)
879 if isinstance(aud, str):
880 return self._is_valid_resource(aud)
881 return False
882
883 def _is_valid_resource(self, resource: str) -> bool:
884 """Check if the given resource matches our server."""
885 return check_resource_allowed(self.resource_url, resource)
886 ```
887
888 For more details, see the [Python SDK documentation](https://github.com/modelcontextprotocol/python-sdk).
889 </Tab>
890
891 <Tab title="C#">
892 You can see the complete C# project in the [sample repository](https://github.com/localden/min-cs-mcp-auth).
893
894 To set up authorization in your MCP server using the MCP C# SDK, you can lean on the standard ASP.NET Core builder pattern. Instead of using the introspection endpoint provided by Keycloak, we will use built-in ASP.NET Core capabilities for token validation.
895
896 ```csharp theme={null}
897 using Microsoft.AspNetCore.Authentication.JwtBearer;
898 using Microsoft.IdentityModel.Tokens;
899 using ModelContextProtocol.AspNetCore.Authentication;
900 using ProtectedMcpServer.Tools;
901 using System.Security.Claims;
902
903 var builder = WebApplication.CreateBuilder(args);
904
905 var serverUrl = "http://localhost:3000/";
906 var authorizationServerUrl = "http://localhost:8080/realms/master/";
907
908 builder.Services.AddAuthentication(options =>
909 {
910 options.DefaultChallengeScheme = McpAuthenticationDefaults.AuthenticationScheme;
911 options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
912 })
913 .AddJwtBearer(options =>
914 {
915 options.Authority = authorizationServerUrl;
916 var normalizedServerAudience = serverUrl.TrimEnd('/');
917 options.TokenValidationParameters = new TokenValidationParameters
918 {
919 ValidIssuer = authorizationServerUrl,
920 ValidAudiences = new[] { normalizedServerAudience, serverUrl },
921 AudienceValidator = (audiences, securityToken, validationParameters) =>
922 {
923 if (audiences == null) return false;
924 foreach (var aud in audiences)
925 {
926 if (string.Equals(aud.TrimEnd('/'), normalizedServerAudience, StringComparison.OrdinalIgnoreCase))
927 {
928 return true;
929 }
930 }
931 return false;
932 }
933 };
934
935 options.RequireHttpsMetadata = false; // Set to true in production
936
937 options.Events = new JwtBearerEvents
938 {
939 OnTokenValidated = context =>
940 {
941 var name = context.Principal?.Identity?.Name ?? "unknown";
942 var email = context.Principal?.FindFirstValue("preferred_username") ?? "unknown";
943 Console.WriteLine($"Token validated for: {name} ({email})");
944 return Task.CompletedTask;
945 },
946 OnAuthenticationFailed = context =>
947 {
948 Console.WriteLine($"Authentication failed: {context.Exception.Message}");
949 return Task.CompletedTask;
950 },
951 };
952 })
953 .AddMcp(options =>
954 {
955 options.ResourceMetadata = new()
956 {
957 Resource = new Uri(serverUrl),
958 ResourceDocumentation = new Uri("https://docs.example.com/api/math"),
959 AuthorizationServers = { new Uri(authorizationServerUrl) },
960 ScopesSupported = ["mcp:tools"]
961 };
962 });
963
964 builder.Services.AddAuthorization();
965
966 builder.Services.AddHttpContextAccessor();
967 builder.Services.AddMcpServer()
968 .WithTools<MathTools>()
969 .WithHttpTransport();
970
971 var app = builder.Build();
972
973 app.UseAuthentication();
974 app.UseAuthorization();
975
976 app.MapMcp().RequireAuthorization();
977
978 Console.WriteLine($"Starting MCP server with authorization at {serverUrl}");
979 Console.WriteLine($"Using Keycloak server at {authorizationServerUrl}");
980 Console.WriteLine($"Protected Resource Metadata URL: {serverUrl}.well-known/oauth-protected-resource");
981 Console.WriteLine("Exposed Math tools: Add, Multiply");
982 Console.WriteLine("Press Ctrl+C to stop the server");
983
984 app.Run(serverUrl);
985 ```
986
987 For more details, see the [C# SDK documentation](https://github.com/modelcontextprotocol/csharp-sdk).
988 </Tab>
989</Tabs>
950});
951
952builder.Services.AddAuthorization();
953
954builder.Services.AddHttpContextAccessor();
955builder.Services.AddMcpServer()
956 .WithTools<MathTools>()
957 .WithHttpTransport();
958
959var app = builder.Build();
960
961app.UseAuthentication();
962app.UseAuthorization();
963
964app.MapMcp().RequireAuthorization();
965
966Console.WriteLine($"Starting MCP server with authorization at {serverUrl}");
967Console.WriteLine($"Using Keycloak server at {authorizationServerUrl}");
968Console.WriteLine($"Protected Resource Metadata URL: {serverUrl}.well-known/oauth-protected-resource");
969Console.WriteLine("Exposed Math tools: Add, Multiply");
970Console.WriteLine("Press Ctrl+C to stop the server");
971
972app.Run(serverUrl);
973```
974
975For more details, see the [C# SDK documentation](https://github.com/modelcontextprotocol/csharp-sdk).
990976
991977## Testing the MCP Server
992978
from line 989
1003989
1004990On connection, you will be taken to the browser, where you will be prompted to consent to Visual Studio Code having access to the `mcp:tools` scope.
1005991
1006<Frame>
1007 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/keycloak-vscode.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=d5183fb7c257993aed1b2246f0bbbb27" alt="Keycloak consent form for VS Code." width="1915" height="1536" data-path="images/tutorial-authorization/keycloak-vscode.png" />
1008</Frame>
992
1009993
1010994After consenting, you will see the tools listed right above the server entry in `mcp.json`.
1011995
1012<Frame>
1013 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/tools-vs-code.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=f7c34d1bf115fe6934e01b4a5a91168b" alt="Tools listed in VS Code." width="496" height="160" data-path="images/tutorial-authorization/tools-vs-code.png" />
1014</Frame>
996
1015997
1016998You will be able to invoke individual tools with the help of the `#` sign in the chat view.
1017999
1018<Frame>
1019 <img src="https://mintcdn.com/mcp/sAd4SGUO-cEUqgzn/images/tutorial-authorization/tools-vs-code-invoke.png?fit=max&auto=format&n=sAd4SGUO-cEUqgzn&q=85&s=76cbef68e48821a3c5467bd20c7e89fe" alt="Invoking MCP tools in VS Code." width="1276" height="396" data-path="images/tutorial-authorization/tools-vs-code-invoke.png" />
1020</Frame>
1000
10211001
10221002## Common Pitfalls and How to Avoid Them
10231003
10241004
docs/2025-11-25/tutorials/security/security_best_practices Changed · +4 / -4 lines
from line 423
423423* Link-local: `169.254.0.0/16` (including cloud metadata endpoints)
424424* Private IPv6 ranges: `fc00::/7`, `fe80::/10`
425425
426<Note>
427 Avoid implementing IP validation manually. Attackers exploit encoding tricks
428 (octal, hex, IPv4-mapped IPv6) that custom parsers often miss.
429</Note>
426> [!NOTE]
427>
428> Avoid implementing IP validation manually. Attackers exploit encoding tricks
429> (octal, hex, IPv4-mapped IPv6) that custom parsers often miss.
430430
431431**Validate Redirect Targets**
432432
docs/2026-07-28/develop/build-client Changed · +2436 / -2452 lines
## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Imports and Setup ### Server Connection Management ### Query Processing Logic ### Interactive Chat Interface ### Main Entry Point ## Key Components Explained ### 1. Client Initialization ### 2. Server Connection ### 3. Query Processing ### 4. Interactive Interface ### 5. Resource Management ## Common Customization Points ## Running the Client ## How It Works ## Best practices ## Troubleshooting ### Server Path Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Basic Client Structure ### Server Connection Management ### Query Processing Logic ### Interactive Chat Interface ### Main Entry Point ## Running the Client ## How It Works ## Best practices ## Troubleshooting ### Server Path Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting Up Your Environment ## How it Works ### MCP Client Configuration ### Chat Implementation ### Build and run ### Advanced Configuration ## System Requirements ## Setting up your environment ## Setting up your API key ## Creating the Client ### Basic Client Structure ### Server connection management ### Query processing logic ### Interactive chat ### Main entry point ## Running the client ## How it works ## Best practices ## Troubleshooting ### Server Path Issues ### Build Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting up your environment ## Setting up your API key ## Creating the Client ### Basic Client Structure ### Query processing logic ## Key Components Explained ### 1. Client Initialization ### 2. Server Connection ### 3. Query Processing ## Running the Client ## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Basic Client Structure ### Server Connection Management ### Query Processing Logic ### Interactive Chat Interface ### Main Entry Point ## Key Components Explained ### 1. Client Initialization ### 2. Server Connection ### 3. Query Processing ### 4. Interactive Interface ### 5. Resource Management ## Running the Client ## How It Works ## Best practices ## Troubleshooting ### Server Path Issues ### Response Timing ### Common Error Messages ## System Requirements ## Setting Up Your Environment ## Setting Up Your API Key ## Creating the Client ### Imports and Client Structure ### Client Initialization ### Server Connection Management ### Converting MCP Tools ### Sending Model Requests ### Query Processing Logic ### Interactive Chat Interface ### Cleanup ### Main Entry Point ### Verify the Complete File ## Running the Client ## How It Works ## Best Practices ## Troubleshooting ### Server Command Issues ### Environment File Issues ### Tool and Response Errors
The two sides of this change are more than 400 edits apart, too far apart to line up, so this is the differ's own diff of it and the words inside a line are not marked.
from line 6
66
77Before you begin, it helps to have gone through our [Build an MCP Server](/docs/2026-07-28/develop/build-server) tutorial so you can understand how clients and servers communicate.
88
9<Tabs>
10 <Tab title="Python">
11 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-python)
12
13 ## System Requirements
14
15 Before starting, ensure your system meets these requirements:
16
17 * Mac or Windows computer
18 * Latest Python version installed
19 * Latest version of `uv` installed
20 * You must use the Python MCP SDK 2.0.0 or higher
21
22 ## Setting Up Your Environment
23
24 First, create a new Python project with `uv`:
25
26 <CodeGroup>
27 ```bash macOS/Linux theme={null}
28 # Create project directory
29 uv init mcp-client
30 cd mcp-client
31
32 # Create virtual environment
33 uv venv
34
35 # Activate virtual environment
36 source .venv/bin/activate
37
38 # Install required packages
39 uv add mcp anthropic python-dotenv
40
41 # Remove boilerplate files
42 rm main.py
43
44 # Create our main file
45 touch client.py
46 ```
47
48 ```powershell Windows theme={null}
49 # Create project directory
50 uv init mcp-client
51 cd mcp-client
52
53 # Create virtual environment
54 uv venv
55
56 # Activate virtual environment
57 .venv\Scripts\activate
58
59 # Install required packages
60 uv add mcp anthropic python-dotenv
61
62 # Remove boilerplate files
63 del main.py
64
65 # Create our main file
66 new-item client.py
67 ```
68 </CodeGroup>
69
70 ## Setting Up Your API Key
71
72 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
73
74 Create a `.env` file to store it:
75
76 ```bash theme={null}
77 echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
78 ```
79
80 Add `.env` to your `.gitignore`:
81
82 ```bash theme={null}
83 echo ".env" >> .gitignore
84 ```
85
86 <Warning>
87 Make sure you keep your `ANTHROPIC_API_KEY` secure!
88 </Warning>
89
90 ## Creating the Client
91
92 ### Imports and Setup
93
94 First, let's set up our imports and the pieces the rest of the file shares:
95
96 ```python theme={null}
97 import asyncio
98 import sys
99
100 from mcp import Client, StdioServerParameters
101 from mcp.client.stdio import stdio_client
102 from mcp_types import TextContent
103
104 from anthropic import Anthropic
105 from dotenv import load_dotenv
106
107 load_dotenv() # load environment variables from .env
108
109 MODEL = "claude-opus-5"
110 anthropic = Anthropic()
111 ```
112
113 `Client` is the single object your program talks to the server through. Listing the tools, calling one, reading a resource: each of those is a method on it.
114
115 ### Server Connection Management
116
117 Next, we'll work out which process to launch for a given server script:
118
119 ```python theme={null}
120 def server_params(server_script_path: str) -> StdioServerParameters:
121 """Describe the subprocess that runs an MCP server
122
123 Args:
124 server_script_path: Path to the server script (.py or .js)
125 """
126 if server_script_path.endswith(".py"):
127 command = "python"
128 elif server_script_path.endswith(".js"):
129 command = "node"
130 else:
131 raise ValueError("Server script must be a .py or .js file")
132
133 return StdioServerParameters(command=command, args=[server_script_path])
134 ```
135
136 `StdioServerParameters` is configuration, not a connection. `stdio_client()` turns it into a stdio transport, and `Client` opens that transport when you enter its `async with` block. We'll do both in `main()`.
137
138 ### Query Processing Logic
139
140 Now let's add the core functionality for processing queries and handling tool calls:
141
142 ```python theme={null}
143 async def process_query(client: Client, query: str) -> str:
144 """Process a query using Claude and available tools"""
145 messages = [
146 {
147 "role": "user",
148 "content": query
149 }
150 ]
151
152 tool_list = await client.list_tools()
153 available_tools = [{
154 "name": tool.name,
155 "description": tool.description,
156 "input_schema": tool.input_schema
157 } for tool in tool_list.tools]
158
159 # Initial Claude API call
9**Python**
10
11[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-python)
12
13## System Requirements
14
15Before starting, ensure your system meets these requirements:
16
17* Mac or Windows computer
18* Latest Python version installed
19* Latest version of `uv` installed
20* You must use the Python MCP SDK 2.0.0 or higher
21
22## Setting Up Your Environment
23
24First, create a new Python project with `uv`:
25
26```bash macOS/Linux theme={null}
27# Create project directory
28uv init mcp-client
29cd mcp-client
30
31# Create virtual environment
32uv venv
33
34# Activate virtual environment
35source .venv/bin/activate
36
37# Install required packages
38uv add mcp anthropic python-dotenv
39
40# Remove boilerplate files
41rm main.py
42
43# Create our main file
44touch client.py
45```
46
47```powershell Windows theme={null}
48# Create project directory
49uv init mcp-client
50cd mcp-client
51
52# Create virtual environment
53uv venv
54
55# Activate virtual environment
56.venv\Scripts\activate
57
58# Install required packages
59uv add mcp anthropic python-dotenv
60
61# Remove boilerplate files
62del main.py
63
64# Create our main file
65new-item client.py
66```
67
68## Setting Up Your API Key
69
70You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
71
72Create a `.env` file to store it:
73
74```bash theme={null}
75echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
76```
77
78Add `.env` to your `.gitignore`:
79
80```bash theme={null}
81echo ".env" >> .gitignore
82```
83
84> [!WARNING]
85>
86> Make sure you keep your `ANTHROPIC_API_KEY` secure!
87
88## Creating the Client
89
90### Imports and Setup
91
92First, let's set up our imports and the pieces the rest of the file shares:
93
94```python theme={null}
95import asyncio
96import sys
97
98from mcp import Client, StdioServerParameters
99from mcp.client.stdio import stdio_client
100from mcp_types import TextContent
101
102from anthropic import Anthropic
103from dotenv import load_dotenv
104
105load_dotenv() # load environment variables from .env
106
107MODEL = "claude-opus-5"
108anthropic = Anthropic()
109```
110
111`Client` is the single object your program talks to the server through. Listing the tools, calling one, reading a resource: each of those is a method on it.
112
113### Server Connection Management
114
115Next, we'll work out which process to launch for a given server script:
116
117```python theme={null}
118def server_params(server_script_path: str) -> StdioServerParameters:
119 """Describe the subprocess that runs an MCP server
120
121 Args:
122 server_script_path: Path to the server script (.py or .js)
123 """
124 if server_script_path.endswith(".py"):
125 command = "python"
126 elif server_script_path.endswith(".js"):
127 command = "node"
128 else:
129 raise ValueError("Server script must be a .py or .js file")
130
131 return StdioServerParameters(command=command, args=[server_script_path])
132```
133
134`StdioServerParameters` is configuration, not a connection. `stdio_client()` turns it into a stdio transport, and `Client` opens that transport when you enter its `async with` block. We'll do both in `main()`.
135
136### Query Processing Logic
137
138Now let's add the core functionality for processing queries and handling tool calls:
139
140```python theme={null}
141async def process_query(client: Client, query: str) -> str:
142 """Process a query using Claude and available tools"""
143 messages = [
144 {
145 "role": "user",
146 "content": query
147 }
148 ]
149
150 tool_list = await client.list_tools()
151 available_tools = [{
152 "name": tool.name,
153 "description": tool.description,
154 "input_schema": tool.input_schema
155 } for tool in tool_list.tools]
156
157 # Initial Claude API call
158 response = anthropic.messages.create(
159 model=MODEL,
160 max_tokens=1000,
161 messages=messages,
162 tools=available_tools
163 )
164
165 # Process response and handle tool calls
166 final_text = []
167 tool_results = []
168
169 for content in response.content:
170 if content.type == 'text':
171 final_text.append(content.text)
172 elif content.type == 'tool_use':
173 tool_name = content.name
174 tool_args = content.input
175
176 # Execute tool call
177 result = await client.call_tool(tool_name, tool_args)
178 final_text.append(f"[Calling tool {tool_name} with args {tool_args}]")
179
180 tool_results.append({
181 "type": "tool_result",
182 "tool_use_id": content.id,
183 "content": "\n".join(
184 block.text
185 for block in result.content
186 if isinstance(block, TextContent)
187 ),
188 "is_error": result.is_error
189 })
190
191 if tool_results:
192 messages.append({"role": "assistant", "content": response.content})
193 messages.append({"role": "user", "content": tool_results})
194
195 # Get next response from Claude
160196 response = anthropic.messages.create(
161197 model=MODEL,
162198 max_tokens=1000,
from line 200
164200 tools=available_tools
165201 )
166202
167 # Process response and handle tool calls
168 final_text = []
169 tool_results = []
170
171203 for content in response.content:
172204 if content.type == 'text':
173205 final_text.append(content.text)
174 elif content.type == 'tool_use':
175 tool_name = content.name
176 tool_args = content.input
177
178 # Execute tool call
179 result = await client.call_tool(tool_name, tool_args)
180 final_text.append(f"[Calling tool {tool_name} with args {tool_args}]")
181
182 tool_results.append({
183 "type": "tool_result",
184 "tool_use_id": content.id,
185 "content": "\n".join(
186 block.text
187 for block in result.content
188 if isinstance(block, TextContent)
189 ),
190 "is_error": result.is_error
191 })
192
193 if tool_results:
194 messages.append({"role": "assistant", "content": response.content})
195 messages.append({"role": "user", "content": tool_results})
196
197 # Get next response from Claude
198 response = anthropic.messages.create(
199 model=MODEL,
200 max_tokens=1000,
201 messages=messages,
202 tools=available_tools
203 )
204
205 for content in response.content:
206 if content.type == 'text':
207 final_text.append(content.text)
208
209 return "\n".join(final_text)
210 ```
211
212 `call_tool` returns a `CallToolResult`. Its `content` is a list of blocks, which is why we narrow to `TextContent` before reading `.text`. A tool that raises does not raise here: it answers with `is_error` set, and passing that flag on lets Claude read the message and try something else.
213
214 ### Interactive Chat Interface
215
216 Now we'll add the chat loop:
217
218 ```python theme={null}
219 async def chat_loop(client: Client) -> None:
220 """Run an interactive chat loop"""
221 print("\nMCP Client Started!")
222 print("Type your queries or 'quit' to exit.")
223
224 while True:
225 try:
226 query = (await asyncio.to_thread(input, "\nQuery: ")).strip()
227 except EOFError:
228 break
229
230 if query.lower() == 'quit':
231 break
232
233 try:
234 response = await process_query(client, query)
235 print("\n" + response)
236 except Exception as e:
237 print(f"\nError: {e}")
238 ```
239
240 `input()` blocks, so it runs on a worker thread. That keeps the event loop free to service the connection while you type.
241
242 ### Main Entry Point
243
244 Finally, we'll add the main execution logic:
245
246 ```python theme={null}
247 async def main() -> None:
248 if len(sys.argv) < 2:
249 print("Usage: python client.py <path_to_server_script>")
250 sys.exit(1)
251
252 async with Client(stdio_client(server_params(sys.argv[1]))) as client:
253 tool_list = await client.list_tools()
254 tool_names = [tool.name for tool in tool_list.tools]
255 print("\nConnected to server with tools:", tool_names)
256
257 await chat_loop(client)
258
259
260 if __name__ == "__main__":
261 asyncio.run(main())
262 ```
263
264 That `async with` is the entire connection lifecycle. Entering it launches the server and agrees a protocol version with it; leaving it disconnects and shuts the subprocess down. There is nothing to close by hand.
265
266 You can find the complete `client.py` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-python/client.py).
267
268 ## Key Components Explained
269
270 ### 1. Client Initialization
271
272 * A single `Client` carries the connection, and `async with` is its whole lifecycle
273 * There is no connect/close pair to call and nothing to clean up afterwards
274 * Configures the Anthropic client for Claude interactions
275
276 ### 2. Server Connection
277
278 * Supports both Python and Node.js servers
279 * Validates server script type
280 * Launches the server as a subprocess and speaks stdio to it
281 * Lists the available tools once the connection is open
282
283 ### 3. Query Processing
284
285 * Maintains conversation context
286 * Handles Claude's responses and tool calls
287 * Manages the message flow between Claude and tools
288 * Combines results into a coherent response
289
290 ### 4. Interactive Interface
291
292 * Provides a simple command-line interface
293 * Handles user input and displays responses
294 * Includes basic error handling
295 * Allows graceful exit
296
297 ### 5. Resource Management
298
299 * Leaving the `async with` block disconnects and shuts the server subprocess down
300 * A failing query is reported without ending the session
301 * Typing `quit`, or closing standard input, exits cleanly
302
303 ## Common Customization Points
304
305 1. **Tool Handling**
306 * Modify `process_query()` to handle specific tool types
307 * Add custom error handling for tool calls
308 * Implement tool-specific response formatting
309
310 2. **Response Processing**
311 * Customize how tool results are formatted
312 * Add response filtering or transformation
313 * Implement custom logging
314
315 3. **User Interface**
316 * Add a GUI or web interface
317 * Implement rich console output
318 * Add command history or auto-completion
319
320 ## Running the Client
321
322 To run your client with any MCP server:
323
324 ```bash theme={null}
325 uv run client.py path/to/server.py # python server
326 uv run client.py path/to/build/index.js # node server
327 ```
328
329 <Note>
330 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python), your command might look something like this: `python client.py .../quickstart-resources/weather-server-python/weather.py`
331 </Note>
332
333 The client will:
334
335 1. Connect to the specified server
336 2. List available tools
337 3. Start an interactive chat session where you can:
338 * Enter queries
339 * See tool executions
340 * Get responses from Claude
341
342 Here's an example of what it should look like if connected to the weather server from the server quickstart:
343
344 <Frame>
345 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/client-claude-cli-python.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=686d6e0ae7c54f807827db111eaed7d4" width="1932" height="1739" data-path="images/client-claude-cli-python.png" />
346 </Frame>
347
348 ## How It Works
349
350 When you submit a query:
351
352 1. The client gets the list of available tools from the server
353 2. Your query is sent to Claude along with tool descriptions
354 3. Claude decides which tools (if any) to use
355 4. The client executes any requested tool calls through the server
356 5. Results are sent back to Claude
357 6. Claude provides a natural language response
358 7. The response is displayed to you
359
360 ## Best practices
361
362 1. **Error Handling**
363 * Check `result.is_error` rather than expecting a failing tool to raise
364 * Provide meaningful error messages
365 * Gracefully handle connection issues
366
367 2. **Resource Management**
368 * Let the `async with` block own the connection
369 * Keep it open for as long as you need the server
370 * Handle server disconnections
371
372 3. **Security**
373 * Store API keys securely in `.env`
374 * Validate server responses
375 * Be cautious with tool permissions
376
377 4. **Tool Names**
378 * Tool names can be validated according to the format specified [here](/specification/2026-07-28/server/tools#tool-names)
379 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
380
381 ## Troubleshooting
382
383 ### Server Path Issues
384
385 * Double-check the path to your server script is correct
386 * Use the absolute path if the relative path isn't working
387 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
388 * Verify the server file has the correct extension (.py for Python or .js for Node.js)
389
390 Example of correct path usage:
391
392 ```bash theme={null}
393 # Relative path
394 uv run client.py ./server/weather.py
395
396 # Absolute path
397 uv run client.py /Users/username/projects/mcp-server/weather.py
398
399 # Windows path (either format works)
400 uv run client.py C:/projects/mcp-server/weather.py
401 uv run client.py C:\\projects\\mcp-server\\weather.py
402 ```
403
404 ### Response Timing
405
406 * The first response might take up to 30 seconds to return
407 * This is normal and happens while:
408 * The server initializes
409 * Claude processes the query
410 * Tools are being executed
411 * Subsequent responses are typically faster
412 * Don't interrupt the process during this initial waiting period
413
414 ### Common Error Messages
415
416 If you see:
417
418 * `FileNotFoundError`: Check your server path
419 * `Connection refused`: Ensure the server is running and the path is correct
420 * `Tool execution failed`: Verify the tool's required environment variables are set
421 * `Timeout error`: Consider raising `read_timeout_seconds` on the `Client`
422 </Tab>
423
424 <Tab title="TypeScript">
425 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-typescript)
426
427 ## System Requirements
428
429 Before starting, ensure your system meets these requirements:
430
431 * Mac or Windows computer
432 * Node.js 20 or higher installed
433 * Latest version of `npm` installed
434 * Anthropic API key (Claude)
435
436 ## Setting Up Your Environment
437
438 First, let's create and set up our project:
439
440 <CodeGroup>
441 ```bash macOS/Linux theme={null}
442 # Create project directory
443 mkdir mcp-client-typescript
444 cd mcp-client-typescript
445
446 # Initialize npm project
447 npm init -y
448
449 # Install dependencies
450 npm install @anthropic-ai/sdk @modelcontextprotocol/client dotenv
451
452 # Install dev dependencies
453 npm install -D @types/node typescript
454
455 # Create source file
456 touch index.ts
457 ```
458
459 ```powershell Windows theme={null}
460 # Create project directory
461 md mcp-client-typescript
462 cd mcp-client-typescript
463
464 # Initialize npm project
465 npm init -y
466
467 # Install dependencies
468 npm install @anthropic-ai/sdk @modelcontextprotocol/client dotenv
469
470 # Install dev dependencies
471 npm install -D @types/node typescript
472
473 # Create source file
474 new-item index.ts
475 ```
476 </CodeGroup>
477
478 Update your `package.json` to set `type: "module"` and a build script:
479
480 ```json package.json theme={null}
206
207 return "\n".join(final_text)
208```
209
210`call_tool` returns a `CallToolResult`. Its `content` is a list of blocks, which is why we narrow to `TextContent` before reading `.text`. A tool that raises does not raise here: it answers with `is_error` set, and passing that flag on lets Claude read the message and try something else.
211
212### Interactive Chat Interface
213
214Now we'll add the chat loop:
215
216```python theme={null}
217async def chat_loop(client: Client) -> None:
218 """Run an interactive chat loop"""
219 print("\nMCP Client Started!")
220 print("Type your queries or 'quit' to exit.")
221
222 while True:
223 try:
224 query = (await asyncio.to_thread(input, "\nQuery: ")).strip()
225 except EOFError:
226 break
227
228 if query.lower() == 'quit':
229 break
230
231 try:
232 response = await process_query(client, query)
233 print("\n" + response)
234 except Exception as e:
235 print(f"\nError: {e}")
236```
237
238`input()` blocks, so it runs on a worker thread. That keeps the event loop free to service the connection while you type.
239
240### Main Entry Point
241
242Finally, we'll add the main execution logic:
243
244```python theme={null}
245async def main() -> None:
246 if len(sys.argv) < 2:
247 print("Usage: python client.py <path_to_server_script>")
248 sys.exit(1)
249
250 async with Client(stdio_client(server_params(sys.argv[1]))) as client:
251 tool_list = await client.list_tools()
252 tool_names = [tool.name for tool in tool_list.tools]
253 print("\nConnected to server with tools:", tool_names)
254
255 await chat_loop(client)
256
257
258if __name__ == "__main__":
259 asyncio.run(main())
260```
261
262That `async with` is the entire connection lifecycle. Entering it launches the server and agrees a protocol version with it; leaving it disconnects and shuts the subprocess down. There is nothing to close by hand.
263
264You can find the complete `client.py` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-python/client.py).
265
266## Key Components Explained
267
268### 1. Client Initialization
269
270* A single `Client` carries the connection, and `async with` is its whole lifecycle
271* There is no connect/close pair to call and nothing to clean up afterwards
272* Configures the Anthropic client for Claude interactions
273
274### 2. Server Connection
275
276* Supports both Python and Node.js servers
277* Validates server script type
278* Launches the server as a subprocess and speaks stdio to it
279* Lists the available tools once the connection is open
280
281### 3. Query Processing
282
283* Maintains conversation context
284* Handles Claude's responses and tool calls
285* Manages the message flow between Claude and tools
286* Combines results into a coherent response
287
288### 4. Interactive Interface
289
290* Provides a simple command-line interface
291* Handles user input and displays responses
292* Includes basic error handling
293* Allows graceful exit
294
295### 5. Resource Management
296
297* Leaving the `async with` block disconnects and shuts the server subprocess down
298* A failing query is reported without ending the session
299* Typing `quit`, or closing standard input, exits cleanly
300
301## Common Customization Points
302
3031. **Tool Handling**
304 * Modify `process_query()` to handle specific tool types
305 * Add custom error handling for tool calls
306 * Implement tool-specific response formatting
307
3082. **Response Processing**
309 * Customize how tool results are formatted
310 * Add response filtering or transformation
311 * Implement custom logging
312
3133. **User Interface**
314 * Add a GUI or web interface
315 * Implement rich console output
316 * Add command history or auto-completion
317
318## Running the Client
319
320To run your client with any MCP server:
321
322```bash theme={null}
323uv run client.py path/to/server.py # python server
324uv run client.py path/to/build/index.js # node server
325```
326
327> [!NOTE]
328>
329> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python), your command might look something like this: `python client.py .../quickstart-resources/weather-server-python/weather.py`
330
331The client will:
332
3331. Connect to the specified server
3342. List available tools
3353. Start an interactive chat session where you can:
336 * Enter queries
337 * See tool executions
338 * Get responses from Claude
339
340Here's an example of what it should look like if connected to the weather server from the server quickstart:
341
342
343
344## How It Works
345
346When you submit a query:
347
3481. The client gets the list of available tools from the server
3492. Your query is sent to Claude along with tool descriptions
3503. Claude decides which tools (if any) to use
3514. The client executes any requested tool calls through the server
3525. Results are sent back to Claude
3536. Claude provides a natural language response
3547. The response is displayed to you
355
356## Best practices
357
3581. **Error Handling**
359 * Check `result.is_error` rather than expecting a failing tool to raise
360 * Provide meaningful error messages
361 * Gracefully handle connection issues
362
3632. **Resource Management**
364 * Let the `async with` block own the connection
365 * Keep it open for as long as you need the server
366 * Handle server disconnections
367
3683. **Security**
369 * Store API keys securely in `.env`
370 * Validate server responses
371 * Be cautious with tool permissions
372
3734. **Tool Names**
374 * Tool names can be validated according to the format specified [here](/specification/2026-07-28/server/tools#tool-names)
375 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
376
377## Troubleshooting
378
379### Server Path Issues
380
381* Double-check the path to your server script is correct
382* Use the absolute path if the relative path isn't working
383* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
384* Verify the server file has the correct extension (.py for Python or .js for Node.js)
385
386Example of correct path usage:
387
388```bash theme={null}
389# Relative path
390uv run client.py ./server/weather.py
391
392# Absolute path
393uv run client.py /Users/username/projects/mcp-server/weather.py
394
395# Windows path (either format works)
396uv run client.py C:/projects/mcp-server/weather.py
397uv run client.py C:\\projects\\mcp-server\\weather.py
398```
399
400### Response Timing
401
402* The first response might take up to 30 seconds to return
403* This is normal and happens while:
404 * The server initializes
405 * Claude processes the query
406 * Tools are being executed
407* Subsequent responses are typically faster
408* Don't interrupt the process during this initial waiting period
409
410### Common Error Messages
411
412If you see:
413
414* `FileNotFoundError`: Check your server path
415* `Connection refused`: Ensure the server is running and the path is correct
416* `Tool execution failed`: Verify the tool's required environment variables are set
417* `Timeout error`: Consider raising `read_timeout_seconds` on the `Client`
418
419**TypeScript**
420
421[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-typescript)
422
423## System Requirements
424
425Before starting, ensure your system meets these requirements:
426
427* Mac or Windows computer
428* Node.js 20 or higher installed
429* Latest version of `npm` installed
430* Anthropic API key (Claude)
431
432## Setting Up Your Environment
433
434First, let's create and set up our project:
435
436```bash macOS/Linux theme={null}
437# Create project directory
438mkdir mcp-client-typescript
439cd mcp-client-typescript
440
441# Initialize npm project
442npm init -y
443
444# Install dependencies
445npm install @anthropic-ai/sdk @modelcontextprotocol/client dotenv
446
447# Install dev dependencies
448npm install -D @types/node typescript
449
450# Create source file
451touch index.ts
452```
453
454```powershell Windows theme={null}
455# Create project directory
456md mcp-client-typescript
457cd mcp-client-typescript
458
459# Initialize npm project
460npm init -y
461
462# Install dependencies
463npm install @anthropic-ai/sdk @modelcontextprotocol/client dotenv
464
465# Install dev dependencies
466npm install -D @types/node typescript
467
468# Create source file
469new-item index.ts
470```
471
472Update your `package.json` to set `type: "module"` and a build script:
473
474```json package.json theme={null}
475{
476 "type": "module",
477 "scripts": {
478 "build": "tsc && chmod 755 build/index.js"
479 }
480}
481```
482
483Create a `tsconfig.json` in the root of your project:
484
485```json tsconfig.json theme={null}
486{
487 "compilerOptions": {
488 "target": "ES2022",
489 "module": "Node16",
490 "moduleResolution": "Node16",
491 "types": ["node"],
492 "outDir": "./build",
493 "rootDir": "./",
494 "strict": true,
495 "esModuleInterop": true,
496 "skipLibCheck": true,
497 "forceConsistentCasingInFileNames": true
498 },
499 "include": ["index.ts"],
500 "exclude": ["node_modules"]
501}
502```
503
504## Setting Up Your API Key
505
506You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
507
508Create a `.env` file to store it:
509
510```bash theme={null}
511echo "ANTHROPIC_API_KEY=<your key here>" > .env
512```
513
514Add `.env` to your `.gitignore`:
515
516```bash theme={null}
517echo ".env" >> .gitignore
518```
519
520> [!WARNING]
521>
522> Make sure you keep your `ANTHROPIC_API_KEY` secure!
523
524## Creating the Client
525
526### Basic Client Structure
527
528First, let's set up our imports and create the basic client class in `index.ts`:
529
530```typescript theme={null}
531import { Anthropic } from "@anthropic-ai/sdk";
532import {
533 MessageParam,
534 Tool,
535} from "@anthropic-ai/sdk/resources/messages/messages.mjs";
536import { Client } from "@modelcontextprotocol/client";
537import { StdioClientTransport } from "@modelcontextprotocol/client/stdio";
538import readline from "readline/promises";
539import dotenv from "dotenv";
540
541dotenv.config();
542
543const ANTHROPIC_API_KEY = process.env.ANTHROPIC_API_KEY;
544if (!ANTHROPIC_API_KEY) {
545 throw new Error("ANTHROPIC_API_KEY is not set");
546}
547
548class MCPClient {
549 private mcp: Client;
550 private anthropic: Anthropic;
551 private transport: StdioClientTransport | null = null;
552 private tools: Tool[] = [];
553
554 constructor() {
555 this.anthropic = new Anthropic({
556 apiKey: ANTHROPIC_API_KEY,
557 });
558 this.mcp = new Client({ name: "mcp-client-cli", version: "1.0.0" });
559 }
560 // methods will go here
561}
562```
563
564### Server Connection Management
565
566Next, we'll implement the method to connect to an MCP server:
567
568```typescript theme={null}
569async connectToServer(serverScriptPath: string) {
570 try {
571 const isJs = serverScriptPath.endsWith(".js");
572 const isPy = serverScriptPath.endsWith(".py");
573 if (!isJs && !isPy) {
574 throw new Error("Server script must be a .js or .py file");
575 }
576 const command = isPy
577 ? process.platform === "win32"
578 ? "python"
579 : "python3"
580 : process.execPath;
581
582 this.transport = new StdioClientTransport({
583 command,
584 args: [serverScriptPath],
585 });
586 await this.mcp.connect(this.transport);
587
588 const toolsResult = await this.mcp.listTools();
589 this.tools = toolsResult.tools.map((tool) => {
590 return {
591 name: tool.name,
592 description: tool.description,
593 input_schema: tool.inputSchema,
594 };
595 });
596 console.log(
597 "Connected to server with tools:",
598 this.tools.map(({ name }) => name)
599 );
600 } catch (e) {
601 console.log("Failed to connect to MCP server: ", e);
602 throw e;
603 }
604}
605```
606
607### Query Processing Logic
608
609Now let's add the core functionality for processing queries and handling tool calls:
610
611```typescript theme={null}
612async processQuery(query: string) {
613 const messages: MessageParam[] = [
481614 {
482 "type": "module",
483 "scripts": {
484 "build": "tsc && chmod 755 build/index.js"
485 }
486 }
487 ```
488
489 Create a `tsconfig.json` in the root of your project:
490
491 ```json tsconfig.json theme={null}
492 {
493 "compilerOptions": {
494 "target": "ES2022",
495 "module": "Node16",
496 "moduleResolution": "Node16",
497 "types": ["node"],
498 "outDir": "./build",
499 "rootDir": "./",
500 "strict": true,
501 "esModuleInterop": true,
502 "skipLibCheck": true,
503 "forceConsistentCasingInFileNames": true
504 },
505 "include": ["index.ts"],
506 "exclude": ["node_modules"]
507 }
508 ```
509
510 ## Setting Up Your API Key
511
512 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
513
514 Create a `.env` file to store it:
515
516 ```bash theme={null}
517 echo "ANTHROPIC_API_KEY=<your key here>" > .env
518 ```
519
520 Add `.env` to your `.gitignore`:
521
522 ```bash theme={null}
523 echo ".env" >> .gitignore
524 ```
525
526 <Warning>
527 Make sure you keep your `ANTHROPIC_API_KEY` secure!
528 </Warning>
529
530 ## Creating the Client
531
532 ### Basic Client Structure
533
534 First, let's set up our imports and create the basic client class in `index.ts`:
535
536 ```typescript theme={null}
537 import { Anthropic } from "@anthropic-ai/sdk";
538 import {
539 MessageParam,
540 Tool,
541 } from "@anthropic-ai/sdk/resources/messages/messages.mjs";
542 import { Client } from "@modelcontextprotocol/client";
543 import { StdioClientTransport } from "@modelcontextprotocol/client/stdio";
544 import readline from "readline/promises";
545 import dotenv from "dotenv";
546
547 dotenv.config();
548
549 const ANTHROPIC_API_KEY = process.env.ANTHROPIC_API_KEY;
550 if (!ANTHROPIC_API_KEY) {
551 throw new Error("ANTHROPIC_API_KEY is not set");
552 }
553
554 class MCPClient {
555 private mcp: Client;
556 private anthropic: Anthropic;
557 private transport: StdioClientTransport | null = null;
558 private tools: Tool[] = [];
559
560 constructor() {
561 this.anthropic = new Anthropic({
562 apiKey: ANTHROPIC_API_KEY,
563 });
564 this.mcp = new Client({ name: "mcp-client-cli", version: "1.0.0" });
565 }
566 // methods will go here
567 }
568 ```
569
570 ### Server Connection Management
571
572 Next, we'll implement the method to connect to an MCP server:
573
574 ```typescript theme={null}
575 async connectToServer(serverScriptPath: string) {
576 try {
577 const isJs = serverScriptPath.endsWith(".js");
578 const isPy = serverScriptPath.endsWith(".py");
579 if (!isJs && !isPy) {
580 throw new Error("Server script must be a .js or .py file");
581 }
582 const command = isPy
583 ? process.platform === "win32"
584 ? "python"
585 : "python3"
586 : process.execPath;
587
588 this.transport = new StdioClientTransport({
589 command,
590 args: [serverScriptPath],
591 });
592 await this.mcp.connect(this.transport);
593
594 const toolsResult = await this.mcp.listTools();
595 this.tools = toolsResult.tools.map((tool) => {
596 return {
597 name: tool.name,
598 description: tool.description,
599 input_schema: tool.inputSchema,
600 };
601 });
602 console.log(
603 "Connected to server with tools:",
604 this.tools.map(({ name }) => name)
605 );
606 } catch (e) {
607 console.log("Failed to connect to MCP server: ", e);
608 throw e;
609 }
610 }
611 ```
612
613 ### Query Processing Logic
614
615 Now let's add the core functionality for processing queries and handling tool calls:
616
617 ```typescript theme={null}
618 async processQuery(query: string) {
619 const messages: MessageParam[] = [
620 {
621 role: "user",
622 content: query,
623 },
624 ];
615 role: "user",
616 content: query,
617 },
618 ];
619
620 const response = await this.anthropic.messages.create({
621 model: "claude-opus-5",
622 max_tokens: 1000,
623 messages,
624 tools: this.tools,
625 });
626
627 const finalText = [];
628
629 for (const content of response.content) {
630 if (content.type === "text") {
631 finalText.push(content.text);
632 } else if (content.type === "tool_use") {
633 const toolName = content.name;
634 const toolArgs = content.input as { [x: string]: unknown } | undefined;
635
636 const result = await this.mcp.callTool({
637 name: toolName,
638 arguments: toolArgs,
639 });
640 finalText.push(
641 `[Calling tool ${toolName} with args ${JSON.stringify(toolArgs)}]`
642 );
643
644 messages.push({
645 role: "user",
646 content: result.content
647 .filter((block) => block.type === "text")
648 .map((block) => block.text)
649 .join("\n"),
650 });
625651
626652 const response = await this.anthropic.messages.create({
627653 model: "claude-opus-5",
628654 max_tokens: 1000,
629655 messages,
630 tools: this.tools,
631656 });
632657
633 const finalText = [];
634
635 for (const content of response.content) {
636 if (content.type === "text") {
637 finalText.push(content.text);
638 } else if (content.type === "tool_use") {
639 const toolName = content.name;
640 const toolArgs = content.input as { [x: string]: unknown } | undefined;
641
642 const result = await this.mcp.callTool({
643 name: toolName,
644 arguments: toolArgs,
645 });
646 finalText.push(
647 `[Calling tool ${toolName} with args ${JSON.stringify(toolArgs)}]`
648 );
649
650 messages.push({
651 role: "user",
652 content: result.content
653 .filter((block) => block.type === "text")
654 .map((block) => block.text)
655 .join("\n"),
656 });
657
658 const response = await this.anthropic.messages.create({
659 model: "claude-opus-5",
660 max_tokens: 1000,
661 messages,
662 });
663
664 finalText.push(
665 response.content[0].type === "text" ? response.content[0].text : ""
666 );
667 }
658 finalText.push(
659 response.content[0].type === "text" ? response.content[0].text : ""
660 );
661 }
662 }
663
664 return finalText.join("\n");
665}
666```
667
668### Interactive Chat Interface
669
670Now we'll add the chat loop and cleanup functionality:
671
672```typescript theme={null}
673async chatLoop() {
674 const rl = readline.createInterface({
675 input: process.stdin,
676 output: process.stdout,
677 });
678
679 try {
680 console.log("\nMCP Client Started!");
681 console.log("Type your queries or 'quit' to exit.");
682
683 while (true) {
684 const message = await rl.question("\nQuery: ");
685 if (message.toLowerCase() === "quit") {
686 break;
668687 }
669
670 return finalText.join("\n");
688 const response = await this.processQuery(message);
689 console.log("\n" + response);
671690 }
672 ```
673
674 ### Interactive Chat Interface
675
676 Now we'll add the chat loop and cleanup functionality:
677
678 ```typescript theme={null}
679 async chatLoop() {
680 const rl = readline.createInterface({
681 input: process.stdin,
682 output: process.stdout,
683 });
684
685 try {
686 console.log("\nMCP Client Started!");
687 console.log("Type your queries or 'quit' to exit.");
688
689 while (true) {
690 const message = await rl.question("\nQuery: ");
691 if (message.toLowerCase() === "quit") {
692 break;
693 }
694 const response = await this.processQuery(message);
695 console.log("\n" + response);
696 }
697 } finally {
698 rl.close();
691 } finally {
692 rl.close();
693 }
694}
695
696async cleanup() {
697 await this.mcp.close();
698}
699```
700
701### Main Entry Point
702
703Finally, we'll add the main execution logic:
704
705```typescript theme={null}
706async function main() {
707 if (process.argv.length < 3) {
708 console.log("Usage: node index.ts <path_to_server_script>");
709 return;
710 }
711 const mcpClient = new MCPClient();
712 try {
713 await mcpClient.connectToServer(process.argv[2]);
714 await mcpClient.chatLoop();
715 } catch (e) {
716 console.error("Error:", e);
717 await mcpClient.cleanup();
718 process.exit(1);
719 } finally {
720 await mcpClient.cleanup();
721 process.exit(0);
722 }
723}
724
725main();
726```
727
728## Running the Client
729
730To run your client with any MCP server:
731
732```bash theme={null}
733# Build TypeScript
734npm run build
735
736# Run the client
737node build/index.js path/to/server.py # python server
738node build/index.js path/to/build/index.js # node server
739```
740
741> [!NOTE]
742>
743> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript), your command might look something like this: `node build/index.js .../quickstart-resources/weather-server-typescript/build/index.js`
744
745**The client will:**
746
7471. Connect to the specified server
7482. List available tools
7493. Start an interactive chat session where you can:
750 * Enter queries
751 * See tool executions
752 * Get responses from Claude
753
754## How It Works
755
756When you submit a query:
757
7581. The client gets the list of available tools from the server
7592. Your query is sent to Claude along with tool descriptions
7603. Claude decides which tools (if any) to use
7614. The client executes any requested tool calls through the server
7625. Results are sent back to Claude
7636. Claude provides a natural language response
7647. The response is displayed to you
765
766## Best practices
767
7681. **Error Handling**
769 * Use TypeScript's type system for better error detection
770 * Wrap tool calls in try-catch blocks
771 * Provide meaningful error messages
772 * Gracefully handle connection issues
773
7742. **Security**
775 * Store API keys securely in `.env`
776 * Validate server responses
777 * Be cautious with tool permissions
778
779## Troubleshooting
780
781### Server Path Issues
782
783* Double-check the path to your server script is correct
784* Use the absolute path if the relative path isn't working
785* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
786* Verify the server file has the correct extension (.js for Node.js or .py for Python)
787
788Example of correct path usage:
789
790```bash theme={null}
791# Relative path
792node build/index.js ./server/build/index.js
793
794# Absolute path
795node build/index.js /Users/username/projects/mcp-server/build/index.js
796
797# Windows path (either format works)
798node build/index.js C:/projects/mcp-server/build/index.js
799node build/index.js C:\\projects\\mcp-server\\build\\index.js
800```
801
802### Response Timing
803
804* The first response might take up to 30 seconds to return
805* This is normal and happens while:
806 * The server initializes
807 * Claude processes the query
808 * Tools are being executed
809* Subsequent responses are typically faster
810* Don't interrupt the process during this initial waiting period
811
812### Common Error Messages
813
814If you see:
815
816* `Error: Cannot find module`: Check your build folder and ensure TypeScript compilation succeeded
817* `Connection refused`: Ensure the server is running and the path is correct
818* `Tool execution failed`: Verify the tool's required environment variables are set
819* `ANTHROPIC_API_KEY is not set`: Check your .env file and environment variables
820* `TypeError`: Ensure you're using the correct types for tool arguments
821* `BadRequestError`: Ensure you have enough credits to access the Anthropic API
822
823**Java**
824
825> [!NOTE]
826>
827> This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
828> To learn how to create sync and async MCP Clients manually, consult the [Java SDK Client](https://java.sdk.modelcontextprotocol.io/) documentation.
829
830This example demonstrates how to build an interactive chatbot that combines Spring AI's Model Context Protocol (MCP) with the [Brave Search MCP Server](https://github.com/modelcontextprotocol/servers-archived/tree/main/src/brave-search). The application creates a conversational interface powered by Anthropic's Claude AI model that can perform internet searches through Brave Search, enabling natural language interactions with real-time web data.
831[You can find the complete code for this tutorial here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/web-search/brave-chatbot)
832
833## System Requirements
834
835Before starting, ensure your system meets these requirements:
836
837* Java 17 or higher
838* Maven 3.6+
839* npx package manager
840* Anthropic API key (Claude)
841* Brave Search API key
842
843## Setting Up Your Environment
844
8451. Install npx (Node Package eXecute):
846 First, make sure to install [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm)
847 and then run:
848
849 ```bash theme={null}
850 npm install -g npx
851 ```
852
8532. Clone the repository:
854
855 ```bash theme={null}
856 git clone https://github.com/spring-projects/spring-ai-examples.git
857 cd model-context-protocol/web-search/brave-chatbot
858 ```
859
8603. Set up your API keys:
861
862 ```bash theme={null}
863 export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
864 export BRAVE_API_KEY='your-brave-api-key-here'
865 ```
866
8674. Build the application:
868
869 ```bash theme={null}
870 ./mvnw clean install
871 ```
872
8735. Run the application using Maven:
874 ```bash theme={null}
875 ./mvnw spring-boot:run
876 ```
877
878> [!WARNING]
879>
880> Make sure you keep your `ANTHROPIC_API_KEY` and `BRAVE_API_KEY` keys secure!
881
882## How it Works
883
884The application integrates Spring AI with the Brave Search MCP server through several components:
885
886### MCP Client Configuration
887
8881. Required dependencies in pom.xml:
889
890```xml theme={null}
891<dependency>
892 <groupId>org.springframework.ai</groupId>
893 <artifactId>spring-ai-starter-mcp-client</artifactId>
894</dependency>
895<dependency>
896 <groupId>org.springframework.ai</groupId>
897 <artifactId>spring-ai-starter-model-anthropic</artifactId>
898</dependency>
899```
900
9012. Application properties (application.yml):
902
903```yml theme={null}
904spring:
905 ai:
906 mcp:
907 client:
908 enabled: true
909 name: brave-search-client
910 version: 1.0.0
911 type: SYNC
912 request-timeout: 20s
913 stdio:
914 root-change-notification: true
915 servers-configuration: classpath:/mcp-servers-config.json
916 toolcallback:
917 enabled: true
918 anthropic:
919 api-key: ${ANTHROPIC_API_KEY}
920```
921
922This activates the `spring-ai-starter-mcp-client` to create one or more `McpClient`s based on the provided server configuration.
923The `spring.ai.mcp.client.toolcallback.enabled=true` property enables the tool callback mechanism, that automatically registers all MCP tool as spring ai tools.
924It is disabled by default.
925
9263. MCP Server Configuration (`mcp-servers-config.json`):
927
928```json theme={null}
929{
930 "mcpServers": {
931 "brave-search": {
932 "command": "npx",
933 "args": ["-y", "@modelcontextprotocol/server-brave-search"],
934 "env": {
935 "BRAVE_API_KEY": "<PUT YOUR BRAVE API KEY>"
699936 }
700937 }
701
702 async cleanup() {
703 await this.mcp.close();
938 }
939}
940```
941
942### Chat Implementation
943
944The chatbot is implemented using Spring AI's ChatClient with MCP tool integration:
945
946```java theme={null}
947var chatClient = chatClientBuilder
948 .defaultSystem("You are useful assistant, expert in AI and Java.")
949 .defaultToolCallbacks((Object[]) mcpToolAdapter.toolCallbacks())
950 .defaultAdvisors(new MessageChatMemoryAdvisor(new InMemoryChatMemory()))
951 .build();
952```
953
954Key features:
955
956* Uses Claude AI model for natural language understanding
957* Integrates Brave Search through MCP for real-time web search capabilities
958* Maintains conversation memory using InMemoryChatMemory
959* Runs as an interactive command-line application
960
961### Build and run
962
963```bash theme={null}
964./mvnw clean install
965java -jar ./target/ai-mcp-brave-chatbot-0.0.1-SNAPSHOT.jar
966```
967
968or
969
970```bash theme={null}
971./mvnw spring-boot:run
972```
973
974The application will start an interactive chat session where you can ask questions. The chatbot will use Brave Search when it needs to find information from the internet to answer your queries.
975
976The chatbot can:
977
978* Answer questions using its built-in knowledge
979* Perform web searches when needed using Brave Search
980* Remember context from previous messages in the conversation
981* Combine information from multiple sources to provide comprehensive answers
982
983### Advanced Configuration
984
985The MCP client supports additional configuration options:
986
987* Client customization through `McpClientCustomizer<McpClient.SyncSpec>` or `McpClientCustomizer<McpClient.AsyncSpec>` beans
988* Multiple clients with multiple transport types: `STDIO` and Streamable HTTP
989* Integration with Spring AI's tool execution framework
990* Automatic client initialization and lifecycle management
991
992To connect to a remote MCP server over Streamable HTTP, configure a connection URL:
993
994```properties theme={null}
995spring.ai.mcp.client.streamable-http.connections.server1.url=http://localhost:8080
996```
997
998For WebFlux-based applications, you can use the WebFlux starter instead:
999
1000```xml theme={null}
1001<dependency>
1002 <groupId>org.springframework.ai</groupId>
1003 <artifactId>spring-ai-starter-mcp-client-webflux</artifactId>
1004</dependency>
1005```
1006
1007This provides similar functionality but uses a WebFlux-based Streamable HTTP transport implementation, recommended for production deployments.
1008
1009**Kotlin**
1010
1011[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/kotlin-mcp-client)
1012
1013## System Requirements
1014
1015Before starting, ensure your system meets these requirements:
1016
1017* JDK 11 or higher
1018* Anthropic API key (Claude)
1019
1020## Setting up your environment
1021
1022First, let's install `java` and `gradle` if you haven't already.
1023You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1024Verify your `java` installation:
1025
1026```bash theme={null}
1027java --version
1028```
1029
1030Now, let's create and set up your project:
1031
1032```bash macOS/Linux theme={null}
1033# Create a new directory for our project
1034mkdir kotlin-mcp-client
1035cd kotlin-mcp-client
1036
1037# Initialize a new kotlin project
1038gradle init
1039```
1040
1041```powershell Windows theme={null}
1042# Create a new directory for our project
1043md kotlin-mcp-client
1044cd kotlin-mcp-client
1045# Initialize a new kotlin project
1046gradle init
1047```
1048
1049After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1050
1051Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1052
1053After creating the project, replace the contents of your `build.gradle.kts` with:
1054
1055```kotlin build.gradle.kts theme={null}
1056// Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1057val mcpVersion = "0.9.0"
1058val ktorVersion = "3.2.3"
1059val anthropicVersion = "2.15.0"
1060val slf4jVersion = "2.0.17"
1061
1062plugins {
1063 kotlin("jvm") version "2.3.20"
1064 id("com.gradleup.shadow") version "8.3.9"
1065 application
1066}
1067
1068application {
1069 mainClass.set("MainKt")
1070}
1071
1072dependencies {
1073 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1074 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1075 implementation("com.anthropic:anthropic-java:$anthropicVersion")
1076 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1077}
1078```
1079
1080Verify that everything is set up correctly:
1081
1082```bash theme={null}
1083./gradlew build
1084```
1085
1086## Setting up your API key
1087
1088You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1089
1090Set up your API key:
1091
1092```bash theme={null}
1093export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
1094```
1095
1096> [!WARNING]
1097>
1098> Make sure you keep your `ANTHROPIC_API_KEY` secure!
1099
1100## Creating the Client
1101
1102### Basic Client Structure
1103
1104First, let's create the basic client class:
1105
1106```kotlin theme={null}
1107class MCPClient(apiKey: String) : AutoCloseable {
1108 private val anthropic = AnthropicOkHttpClient.builder()
1109 .apiKey(apiKey)
1110 .build()
1111
1112 private val mcp: Client = Client(
1113 clientInfo = Implementation(name = "mcp-client-cli", version = "1.0.0")
1114 )
1115 private var serverProcess: Process? = null
1116 private lateinit var tools: List<ToolUnion>
1117
1118 // methods will go here
1119
1120 override fun close() {
1121 runBlocking {
1122 mcp.close()
1123 }
1124 serverProcess?.destroy()
1125 anthropic.close()
7041126 }
705 ```
706
707 ### Main Entry Point
708
709 Finally, we'll add the main execution logic:
710
711 ```typescript theme={null}
712 async function main() {
713 if (process.argv.length < 3) {
714 console.log("Usage: node index.ts <path_to_server_script>");
715 return;
716 }
717 const mcpClient = new MCPClient();
718 try {
719 await mcpClient.connectToServer(process.argv[2]);
720 await mcpClient.chatLoop();
721 } catch (e) {
722 console.error("Error:", e);
723 await mcpClient.cleanup();
724 process.exit(1);
725 } finally {
726 await mcpClient.cleanup();
727 process.exit(0);
728 }
1127}
1128```
1129
1130### Server connection management
1131
1132Next, we'll implement the method to connect to an MCP server:
1133
1134```kotlin theme={null}
1135suspend fun connectToServer(serverScriptPath: String) {
1136 val command = buildList {
1137 when (serverScriptPath.substringAfterLast(".")) {
1138 "js" -> add("node")
1139 "py" -> add(if (System.getProperty("os.name").lowercase().contains("win")) "python" else "python3")
1140 "jar" -> addAll(listOf("java", "-jar"))
1141 else -> throw IllegalArgumentException("Server script must be a .js, .py or .jar file")
1142 }
1143 add(serverScriptPath)
7291144 }
7301145
731 main();
732 ```
733
734 ## Running the Client
735
736 To run your client with any MCP server:
737
738 ```bash theme={null}
739 # Build TypeScript
740 npm run build
741
742 # Run the client
743 node build/index.js path/to/server.py # python server
744 node build/index.js path/to/build/index.js # node server
745 ```
746
747 <Note>
748 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript), your command might look something like this: `node build/index.js .../quickstart-resources/weather-server-typescript/build/index.js`
749 </Note>
750
751 **The client will:**
752
753 1. Connect to the specified server
754 2. List available tools
755 3. Start an interactive chat session where you can:
756 * Enter queries
757 * See tool executions
758 * Get responses from Claude
759
760 ## How It Works
761
762 When you submit a query:
763
764 1. The client gets the list of available tools from the server
765 2. Your query is sent to Claude along with tool descriptions
766 3. Claude decides which tools (if any) to use
767 4. The client executes any requested tool calls through the server
768 5. Results are sent back to Claude
769 6. Claude provides a natural language response
770 7. The response is displayed to you
771
772 ## Best practices
773
774 1. **Error Handling**
775 * Use TypeScript's type system for better error detection
776 * Wrap tool calls in try-catch blocks
777 * Provide meaningful error messages
778 * Gracefully handle connection issues
779
780 2. **Security**
781 * Store API keys securely in `.env`
782 * Validate server responses
783 * Be cautious with tool permissions
784
785 ## Troubleshooting
786
787 ### Server Path Issues
788
789 * Double-check the path to your server script is correct
790 * Use the absolute path if the relative path isn't working
791 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
792 * Verify the server file has the correct extension (.js for Node.js or .py for Python)
793
794 Example of correct path usage:
795
796 ```bash theme={null}
797 # Relative path
798 node build/index.js ./server/build/index.js
799
800 # Absolute path
801 node build/index.js /Users/username/projects/mcp-server/build/index.js
802
803 # Windows path (either format works)
804 node build/index.js C:/projects/mcp-server/build/index.js
805 node build/index.js C:\\projects\\mcp-server\\build\\index.js
806 ```
807
808 ### Response Timing
809
810 * The first response might take up to 30 seconds to return
811 * This is normal and happens while:
812 * The server initializes
813 * Claude processes the query
814 * Tools are being executed
815 * Subsequent responses are typically faster
816 * Don't interrupt the process during this initial waiting period
817
818 ### Common Error Messages
819
820 If you see:
821
822 * `Error: Cannot find module`: Check your build folder and ensure TypeScript compilation succeeded
823 * `Connection refused`: Ensure the server is running and the path is correct
824 * `Tool execution failed`: Verify the tool's required environment variables are set
825 * `ANTHROPIC_API_KEY is not set`: Check your .env file and environment variables
826 * `TypeError`: Ensure you're using the correct types for tool arguments
827 * `BadRequestError`: Ensure you have enough credits to access the Anthropic API
828 </Tab>
829
830 <Tab title="Java">
831 <Note>
832 This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
833 To learn how to create sync and async MCP Clients manually, consult the [Java SDK Client](https://java.sdk.modelcontextprotocol.io/) documentation.
834 </Note>
835
836 This example demonstrates how to build an interactive chatbot that combines Spring AI's Model Context Protocol (MCP) with the [Brave Search MCP Server](https://github.com/modelcontextprotocol/servers-archived/tree/main/src/brave-search). The application creates a conversational interface powered by Anthropic's Claude AI model that can perform internet searches through Brave Search, enabling natural language interactions with real-time web data.
837 [You can find the complete code for this tutorial here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/web-search/brave-chatbot)
838
839 ## System Requirements
840
841 Before starting, ensure your system meets these requirements:
842
843 * Java 17 or higher
844 * Maven 3.6+
845 * npx package manager
846 * Anthropic API key (Claude)
847 * Brave Search API key
848
849 ## Setting Up Your Environment
850
851 1. Install npx (Node Package eXecute):
852 First, make sure to install [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm)
853 and then run:
854
855 ```bash theme={null}
856 npm install -g npx
857 ```
858
859 2. Clone the repository:
860
861 ```bash theme={null}
862 git clone https://github.com/spring-projects/spring-ai-examples.git
863 cd model-context-protocol/web-search/brave-chatbot
864 ```
865
866 3. Set up your API keys:
867
868 ```bash theme={null}
869 export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
870 export BRAVE_API_KEY='your-brave-api-key-here'
871 ```
872
873 4. Build the application:
874
875 ```bash theme={null}
876 ./mvnw clean install
877 ```
878
879 5. Run the application using Maven:
880 ```bash theme={null}
881 ./mvnw spring-boot:run
882 ```
883
884 <Warning>
885 Make sure you keep your `ANTHROPIC_API_KEY` and `BRAVE_API_KEY` keys secure!
886 </Warning>
887
888 ## How it Works
889
890 The application integrates Spring AI with the Brave Search MCP server through several components:
891
892 ### MCP Client Configuration
893
894 1. Required dependencies in pom.xml:
895
896 ```xml theme={null}
897 <dependency>
898 <groupId>org.springframework.ai</groupId>
899 <artifactId>spring-ai-starter-mcp-client</artifactId>
900 </dependency>
901 <dependency>
902 <groupId>org.springframework.ai</groupId>
903 <artifactId>spring-ai-starter-model-anthropic</artifactId>
904 </dependency>
905 ```
906
907 2. Application properties (application.yml):
908
909 ```yml theme={null}
910 spring:
911 ai:
912 mcp:
913 client:
914 enabled: true
915 name: brave-search-client
916 version: 1.0.0
917 type: SYNC
918 request-timeout: 20s
919 stdio:
920 root-change-notification: true
921 servers-configuration: classpath:/mcp-servers-config.json
922 toolcallback:
923 enabled: true
924 anthropic:
925 api-key: ${ANTHROPIC_API_KEY}
926 ```
927
928 This activates the `spring-ai-starter-mcp-client` to create one or more `McpClient`s based on the provided server configuration.
929 The `spring.ai.mcp.client.toolcallback.enabled=true` property enables the tool callback mechanism, that automatically registers all MCP tool as spring ai tools.
930 It is disabled by default.
931
932 3. MCP Server Configuration (`mcp-servers-config.json`):
933
934 ```json theme={null}
935 {
936 "mcpServers": {
937 "brave-search": {
938 "command": "npx",
939 "args": ["-y", "@modelcontextprotocol/server-brave-search"],
940 "env": {
941 "BRAVE_API_KEY": "<PUT YOUR BRAVE API KEY>"
942 }
943 }
944 }
945 }
946 ```
947
948 ### Chat Implementation
949
950 The chatbot is implemented using Spring AI's ChatClient with MCP tool integration:
951
952 ```java theme={null}
953 var chatClient = chatClientBuilder
954 .defaultSystem("You are useful assistant, expert in AI and Java.")
955 .defaultToolCallbacks((Object[]) mcpToolAdapter.toolCallbacks())
956 .defaultAdvisors(new MessageChatMemoryAdvisor(new InMemoryChatMemory()))
957 .build();
958 ```
959
960 Key features:
961
962 * Uses Claude AI model for natural language understanding
963 * Integrates Brave Search through MCP for real-time web search capabilities
964 * Maintains conversation memory using InMemoryChatMemory
965 * Runs as an interactive command-line application
966
967 ### Build and run
968
969 ```bash theme={null}
970 ./mvnw clean install
971 java -jar ./target/ai-mcp-brave-chatbot-0.0.1-SNAPSHOT.jar
972 ```
973
974 or
975
976 ```bash theme={null}
977 ./mvnw spring-boot:run
978 ```
979
980 The application will start an interactive chat session where you can ask questions. The chatbot will use Brave Search when it needs to find information from the internet to answer your queries.
981
982 The chatbot can:
983
984 * Answer questions using its built-in knowledge
985 * Perform web searches when needed using Brave Search
986 * Remember context from previous messages in the conversation
987 * Combine information from multiple sources to provide comprehensive answers
988
989 ### Advanced Configuration
990
991 The MCP client supports additional configuration options:
992
993 * Client customization through `McpClientCustomizer<McpClient.SyncSpec>` or `McpClientCustomizer<McpClient.AsyncSpec>` beans
994 * Multiple clients with multiple transport types: `STDIO` and Streamable HTTP
995 * Integration with Spring AI's tool execution framework
996 * Automatic client initialization and lifecycle management
997
998 To connect to a remote MCP server over Streamable HTTP, configure a connection URL:
999
1000 ```properties theme={null}
1001 spring.ai.mcp.client.streamable-http.connections.server1.url=http://localhost:8080
1002 ```
1003
1004 For WebFlux-based applications, you can use the WebFlux starter instead:
1005
1006 ```xml theme={null}
1007 <dependency>
1008 <groupId>org.springframework.ai</groupId>
1009 <artifactId>spring-ai-starter-mcp-client-webflux</artifactId>
1010 </dependency>
1011 ```
1012
1013 This provides similar functionality but uses a WebFlux-based Streamable HTTP transport implementation, recommended for production deployments.
1014 </Tab>
1015
1016 <Tab title="Kotlin">
1017 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/kotlin-mcp-client)
1018
1019 ## System Requirements
1020
1021 Before starting, ensure your system meets these requirements:
1022
1023 * JDK 11 or higher
1024 * Anthropic API key (Claude)
1025
1026 ## Setting up your environment
1027
1028 First, let's install `java` and `gradle` if you haven't already.
1029 You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1030 Verify your `java` installation:
1031
1032 ```bash theme={null}
1033 java --version
1034 ```
1035
1036 Now, let's create and set up your project:
1037
1038 <CodeGroup>
1039 ```bash macOS/Linux theme={null}
1040 # Create a new directory for our project
1041 mkdir kotlin-mcp-client
1042 cd kotlin-mcp-client
1043
1044 # Initialize a new kotlin project
1045 gradle init
1046 ```
1047
1048 ```powershell Windows theme={null}
1049 # Create a new directory for our project
1050 md kotlin-mcp-client
1051 cd kotlin-mcp-client
1052 # Initialize a new kotlin project
1053 gradle init
1054 ```
1055 </CodeGroup>
1056
1057 After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1058
1059 Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1060
1061 After creating the project, replace the contents of your `build.gradle.kts` with:
1062
1063 ```kotlin build.gradle.kts theme={null}
1064 // Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1065 val mcpVersion = "0.9.0"
1066 val ktorVersion = "3.2.3"
1067 val anthropicVersion = "2.15.0"
1068 val slf4jVersion = "2.0.17"
1069
1070 plugins {
1071 kotlin("jvm") version "2.3.20"
1072 id("com.gradleup.shadow") version "8.3.9"
1073 application
1074 }
1075
1076 application {
1077 mainClass.set("MainKt")
1078 }
1079
1080 dependencies {
1081 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1082 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1083 implementation("com.anthropic:anthropic-java:$anthropicVersion")
1084 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1085 }
1086 ```
1087
1088 Verify that everything is set up correctly:
1089
1090 ```bash theme={null}
1091 ./gradlew build
1092 ```
1093
1094 ## Setting up your API key
1095
1096 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1097
1098 Set up your API key:
1099
1100 ```bash theme={null}
1101 export ANTHROPIC_API_KEY='your-anthropic-api-key-here'
1102 ```
1103
1104 <Warning>
1105 Make sure you keep your `ANTHROPIC_API_KEY` secure!
1106 </Warning>
1107
1108 ## Creating the Client
1109
1110 ### Basic Client Structure
1111
1112 First, let's create the basic client class:
1113
1114 ```kotlin theme={null}
1115 class MCPClient(apiKey: String) : AutoCloseable {
1116 private val anthropic = AnthropicOkHttpClient.builder()
1117 .apiKey(apiKey)
1118 .build()
1119
1120 private val mcp: Client = Client(
1121 clientInfo = Implementation(name = "mcp-client-cli", version = "1.0.0")
1122 )
1123 private var serverProcess: Process? = null
1124 private lateinit var tools: List<ToolUnion>
1125
1126 // methods will go here
1127
1128 override fun close() {
1129 runBlocking {
1130 mcp.close()
1131 }
1132 serverProcess?.destroy()
1133 anthropic.close()
1134 }
1135 }
1136 ```
1137
1138 ### Server connection management
1139
1140 Next, we'll implement the method to connect to an MCP server:
1141
1142 ```kotlin theme={null}
1143 suspend fun connectToServer(serverScriptPath: String) {
1144 val command = buildList {
1145 when (serverScriptPath.substringAfterLast(".")) {
1146 "js" -> add("node")
1147 "py" -> add(if (System.getProperty("os.name").lowercase().contains("win")) "python" else "python3")
1148 "jar" -> addAll(listOf("java", "-jar"))
1149 else -> throw IllegalArgumentException("Server script must be a .js, .py or .jar file")
1150 }
1151 add(serverScriptPath)
1152 }
1153
1154 val process = ProcessBuilder(command).start()
1155 serverProcess = process
1156
1157 val transport = StdioClientTransport(
1158 input = process.inputStream.asSource().buffered(),
1159 output = process.outputStream.asSink().buffered(),
1160 )
1161
1162 mcp.connect(transport)
1163
1164 val toolsResult = mcp.listTools()
1165 tools = toolsResult.tools.map { tool ->
1166 ToolUnion.ofTool(
1167 Tool.builder()
1168 .name(tool.name)
1169 .description(tool.description ?: "")
1170 .inputSchema(
1171 Tool.InputSchema.builder()
1172 .type(JsonValue.from(tool.inputSchema.type))
1173 .properties(tool.inputSchema.properties?.toJsonValue() ?: EmptyJsonObject.toJsonValue())
1174 .putAdditionalProperty("required", JsonValue.from(tool.inputSchema.required))
1175 .build(),
1176 )
1177 .build(),
1178 )
1179 }
1180 println("Connected to server with tools: ${tools.joinToString(", ") { it.tool().get().name() }}")
1181 }
1182 ```
1183
1184 <Accordion title="JsonObject.toJsonValue() helper">
1185 This helper converts a kotlinx.serialization `JsonObject` to an Anthropic SDK `JsonValue` using Jackson:
1186
1187 ```kotlin theme={null}
1188 private fun JsonObject.toJsonValue(): JsonValue {
1189 val mapper = ObjectMapper()
1190 val node = mapper.readTree(this.toString())
1191 return JsonValue.fromJsonNode(node)
1192 }
1193 ```
1194 </Accordion>
1195
1196 ### Query processing logic
1197
1198 Now let's add the core functionality for processing queries and handling tool calls:
1199
1200 ```kotlin theme={null}
1201 suspend fun processQuery(query: String): String {
1202 val messages = mutableListOf(
1203 MessageParam.builder()
1204 .role(MessageParam.Role.USER)
1205 .content(query)
1146 val process = ProcessBuilder(command).start()
1147 serverProcess = process
1148
1149 val transport = StdioClientTransport(
1150 input = process.inputStream.asSource().buffered(),
1151 output = process.outputStream.asSink().buffered(),
1152 )
1153
1154 mcp.connect(transport)
1155
1156 val toolsResult = mcp.listTools()
1157 tools = toolsResult.tools.map { tool ->
1158 ToolUnion.ofTool(
1159 Tool.builder()
1160 .name(tool.name)
1161 .description(tool.description ?: "")
1162 .inputSchema(
1163 Tool.InputSchema.builder()
1164 .type(JsonValue.from(tool.inputSchema.type))
1165 .properties(tool.inputSchema.properties?.toJsonValue() ?: EmptyJsonObject.toJsonValue())
1166 .putAdditionalProperty("required", JsonValue.from(tool.inputSchema.required))
1167 .build(),
1168 )
12061169 .build(),
12071170 )
1208
1209 val response = anthropic.messages().create(
1210 MessageCreateParams.builder()
1211 .model("claude-opus-5")
1212 .maxTokens(1024)
1213 .messages(messages)
1214 .tools(tools)
1215 .build(),
1216 )
1217
1218 val finalText = mutableListOf<String>()
1219 response.content().forEach { content ->
1220 when {
1221 content.isText() -> finalText.add(content.text().get().text())
1222
1223 content.isToolUse() -> {
1224 val toolName = content.toolUse().get().name()
1225 val toolArgs =
1226 content.toolUse().get()._input().convert(object : TypeReference<Map<String, JsonValue>>() {})
1227
1228 val result = mcp.callTool(
1229 name = toolName,
1230 arguments = toolArgs ?: emptyMap(),
1231 )
1232 finalText.add("[Calling tool $toolName with args $toolArgs]")
1233
1234 messages.add(
1235 MessageParam.builder()
1236 .role(MessageParam.Role.USER)
1237 .content(
1238 result.content
1239 .filterIsInstance<TextContent>()
1240 .joinToString("\n") { it.text }
1241 )
1242 .build(),
1243 )
1244
1245 val aiResponse = anthropic.messages().create(
1246 MessageCreateParams.builder()
1247 .model("claude-opus-5")
1248 .maxTokens(1024)
1249 .messages(messages)
1250 .build(),
1251 )
1252
1253 finalText.add(aiResponse.content().first().text().get().text())
1254 }
1255 }
1256 }
1257
1258 return finalText.joinToString("\n")
12591171 }
1260 ```
1261
1262 ### Interactive chat
1263
1264 We'll add the chat loop:
1265
1266 ```kotlin theme={null}
1267 suspend fun chatLoop() {
1268 println("\nMCP Client Started!")
1269 println("Type your queries or 'quit' to exit.")
1270
1271 while (true) {
1272 print("\nQuery: ")
1273 val message = readlnOrNull() ?: break
1274 if (message.trim().lowercase() == "quit") break
1275
1276 try {
1277 val response = processQuery(message)
1278 println("\n$response")
1279 } catch (e: Exception) {
1280 println("\nError: ${e.message}")
1172 println("Connected to server with tools: ${tools.joinToString(", ") { it.tool().get().name() }}")
1173}
1174```
1175
1176> **JsonObject.toJsonValue() helper**
1177>
1178> This helper converts a kotlinx.serialization `JsonObject` to an Anthropic SDK `JsonValue` using Jackson:
1179>
1180> ```kotlin theme={null}
1181> private fun JsonObject.toJsonValue(): JsonValue {
1182> val mapper = ObjectMapper()
1183> val node = mapper.readTree(this.toString())
1184> return JsonValue.fromJsonNode(node)
1185> }
1186> ```
1187
1188### Query processing logic
1189
1190Now let's add the core functionality for processing queries and handling tool calls:
1191
1192```kotlin theme={null}
1193suspend fun processQuery(query: String): String {
1194 val messages = mutableListOf(
1195 MessageParam.builder()
1196 .role(MessageParam.Role.USER)
1197 .content(query)
1198 .build(),
1199 )
1200
1201 val response = anthropic.messages().create(
1202 MessageCreateParams.builder()
1203 .model("claude-opus-5")
1204 .maxTokens(1024)
1205 .messages(messages)
1206 .tools(tools)
1207 .build(),
1208 )
1209
1210 val finalText = mutableListOf<String>()
1211 response.content().forEach { content ->
1212 when {
1213 content.isText() -> finalText.add(content.text().get().text())
1214
1215 content.isToolUse() -> {
1216 val toolName = content.toolUse().get().name()
1217 val toolArgs =
1218 content.toolUse().get()._input().convert(object : TypeReference<Map<String, JsonValue>>() {})
1219
1220 val result = mcp.callTool(
1221 name = toolName,
1222 arguments = toolArgs ?: emptyMap(),
1223 )
1224 finalText.add("[Calling tool $toolName with args $toolArgs]")
1225
1226 messages.add(
1227 MessageParam.builder()
1228 .role(MessageParam.Role.USER)
1229 .content(
1230 result.content
1231 .filterIsInstance<TextContent>()
1232 .joinToString("\n") { it.text }
1233 )
1234 .build(),
1235 )
1236
1237 val aiResponse = anthropic.messages().create(
1238 MessageCreateParams.builder()
1239 .model("claude-opus-5")
1240 .maxTokens(1024)
1241 .messages(messages)
1242 .build(),
1243 )
1244
1245 finalText.add(aiResponse.content().first().text().get().text())
12811246 }
12821247 }
12831248 }
1284 ```
1285
1286 ### Main entry point
1287
1288 Finally, we'll add the main execution function:
1289
1290 ```kotlin theme={null}
1291 fun main(args: Array<String>) = runBlocking {
1292 require(args.isNotEmpty()) { "Usage: java -jar <path> <path_to_server_script>" }
1293
1294 val apiKey = System.getenv("ANTHROPIC_API_KEY")
1295 require(!apiKey.isNullOrBlank()) { "ANTHROPIC_API_KEY environment variable is not set" }
1296
1297 val client = MCPClient(apiKey)
1298 client.use {
1299 client.connectToServer(args.first())
1300 client.chatLoop()
1249
1250 return finalText.joinToString("\n")
1251}
1252```
1253
1254### Interactive chat
1255
1256We'll add the chat loop:
1257
1258```kotlin theme={null}
1259suspend fun chatLoop() {
1260 println("\nMCP Client Started!")
1261 println("Type your queries or 'quit' to exit.")
1262
1263 while (true) {
1264 print("\nQuery: ")
1265 val message = readlnOrNull() ?: break
1266 if (message.trim().lowercase() == "quit") break
1267
1268 try {
1269 val response = processQuery(message)
1270 println("\n$response")
1271 } catch (e: Exception) {
1272 println("\nError: ${e.message}")
13011273 }
13021274 }
1303 ```
1304
1305 ## Running the client
1306
1307 To run your client with any MCP server:
1308
1309 ```bash theme={null}
1310 ./gradlew build
1311
1312 # Run the client
1313 java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.jar # JVM server
1314 java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.py # Python server
1315 java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/build/index.js # Node server
1316 ```
1317
1318 Alternatively, you can run directly with Gradle:
1319
1320 ```bash theme={null}
1321 ./gradlew run --args="path/to/server.jar"
1322 ```
1323
1324 <Note>
1325 If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar .../samples/weather-stdio-server/build/libs/weather-stdio-server-0.1.0-all.jar`
1326 </Note>
1327
1328 **The client will:**
1329
1330 1. Connect to the specified server
1331 2. List available tools
1332 3. Start an interactive chat session where you can:
1333 * Enter queries
1334 * See tool executions
1335 * Get responses from Claude
1336
1337 ## How it works
1338
1339 Here's a high-level workflow schema:
1340
1341 ```mermaid theme={null}
1342 ---
1343 config:
1344 theme: neutral
1345 ---
1346 sequenceDiagram
1347 actor User
1348 participant Client
1349 participant Claude
1350 participant MCP_Server as MCP Server
1351 participant Tools
1352
1353 User->>Client: Send query
1354 Client<<->>MCP_Server: Get available tools
1355 Client->>Claude: Send query with tool descriptions
1356 Claude-->>Client: Decide tool execution
1357 Client->>MCP_Server: Request tool execution
1358 MCP_Server->>Tools: Execute chosen tools
1359 Tools-->>MCP_Server: Return results
1360 MCP_Server-->>Client: Send results
1361 Client->>Claude: Send tool results
1362 Claude-->>Client: Provide final response
1363 Client-->>User: Display response
1364 ```
1365
1366 When you submit a query:
1367
1368 1. The client gets the list of available tools from the server
1369 2. Your query is sent to Claude along with tool descriptions
1370 3. Claude decides which tools (if any) to use
1371 4. The client executes any requested tool calls through the server
1372 5. Results are sent back to Claude
1373 6. Claude provides a natural language response
1374 7. The response is displayed to you
1375
1376 ## Best practices
1377
1378 1. **Error Handling**
1379 * Leverage Kotlin's type system to model errors explicitly
1380 * Wrap external tool and API calls in `try-catch` blocks when exceptions are possible
1381 * Provide clear and meaningful error messages
1382 * Handle network timeouts and connection issues gracefully
1383
1384 2. **Security**
1385 * Store API keys and secrets securely in `local.properties`, environment variables, or secret managers
1386 * Validate all external responses to avoid unexpected or unsafe data usage
1387 * Be cautious with permissions and trust boundaries when using tools
1388
1389 3. **Environment**
1390 * Set `ANTHROPIC_API_KEY` through environment variables rather than hardcoding
1391 * Use `.env` files with appropriate `.gitignore` rules for local development
1392
1393 ## Troubleshooting
1394
1395 ### Server Path Issues
1396
1397 * Double-check the path to your server script is correct
1398 * Use the absolute path if the relative path isn't working
1399 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
1400 * Make sure that the required runtime is installed (java for Java, npm for Node.js, or uv for Python)
1401 * Verify the server file has the correct extension (.jar for Java, .js for Node.js or .py for Python)
1402
1403 Example of correct path usage:
1404
1405 ```bash theme={null}
1406 # Relative path
1407 java -jar build/libs/client.jar ./server/build/libs/server.jar
1408
1409 # Absolute path
1410 java -jar build/libs/client.jar /Users/username/projects/mcp-server/build/libs/server.jar
1411
1412 # Windows path (either format works)
1413 java -jar build/libs/client.jar C:/projects/mcp-server/build/libs/server.jar
1414 java -jar build/libs/client.jar C:\\projects\\mcp-server\\build\\libs\\server.jar
1415 ```
1416
1417 ### Build Issues
1418
1419 * Use `./gradlew build` or `./gradlew shadowJar` (not `./gradlew jar`) to create the shadow JAR with all dependencies
1420 * If you get JDK version errors, ensure your installed JDK version matches or exceeds the `jvmToolchain` setting in `build.gradle.kts`
1421
1422 ### Response Timing
1423
1424 * The first response might take up to 30 seconds to return
1425 * This is normal and happens while:
1426 * The server initializes
1427 * Claude processes the query
1428 * Tools are being executed
1429 * Subsequent responses are typically faster
1430 * Don't interrupt the process during this initial waiting period
1431
1432 ### Common Error Messages
1433
1434 If you see:
1435
1436 * `Connection refused`: Ensure the server is running and the path is correct
1437 * `Tool execution failed`: Verify the tool's required environment variables are set
1438 * `ANTHROPIC_API_KEY is not set`: Check your environment variables
1439 </Tab>
1440
1441 <Tab title="C#">
1442 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartClient)
1443
1444 ## System Requirements
1445
1446 Before starting, ensure your system meets these requirements:
1447
1448 * .NET 8.0 or higher
1449 * Anthropic API key (Claude)
1450 * Windows, Linux, or macOS
1451
1452 ## Setting up your environment
1453
1454 First, create a new .NET project:
1455
1456 ```bash theme={null}
1457 dotnet new console -n QuickstartClient
1458 cd QuickstartClient
1459 ```
1460
1461 Then, add the required dependencies to your project:
1462
1463 ```bash theme={null}
1464 dotnet add package ModelContextProtocol --prerelease
1465 dotnet add package Anthropic.SDK
1466 dotnet add package Microsoft.Extensions.Hosting
1467 dotnet add package Microsoft.Extensions.AI
1468 ```
1469
1470 ## Setting up your API key
1471
1472 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1473
1474 ```bash theme={null}
1475 dotnet user-secrets init
1476 dotnet user-secrets set "ANTHROPIC_API_KEY" "<your key here>"
1477 ```
1478
1479 ## Creating the Client
1480
1481 ### Basic Client Structure
1482
1483 First, let's setup the basic client class in the file `Program.cs`:
1484
1485 ```csharp theme={null}
1486 using Anthropic.SDK;
1487 using Microsoft.Extensions.AI;
1488 using Microsoft.Extensions.Configuration;
1489 using Microsoft.Extensions.Hosting;
1490 using ModelContextProtocol.Client;
1491 using ModelContextProtocol.Protocol.Transport;
1492
1493 var builder = Host.CreateApplicationBuilder(args);
1494
1495 builder.Configuration
1496 .AddEnvironmentVariables()
1497 .AddUserSecrets<Program>();
1498 ```
1499
1500 This creates the beginnings of a .NET console application that can read the API key from user secrets.
1501
1502 Next, we'll setup the MCP Client:
1503
1504 ```csharp theme={null}
1505 var (command, arguments) = GetCommandAndArguments(args);
1506
1507 var clientTransport = new StdioClientTransport(new()
1275}
1276```
1277
1278### Main entry point
1279
1280Finally, we'll add the main execution function:
1281
1282```kotlin theme={null}
1283fun main(args: Array<String>) = runBlocking {
1284 require(args.isNotEmpty()) { "Usage: java -jar <path> <path_to_server_script>" }
1285
1286 val apiKey = System.getenv("ANTHROPIC_API_KEY")
1287 require(!apiKey.isNullOrBlank()) { "ANTHROPIC_API_KEY environment variable is not set" }
1288
1289 val client = MCPClient(apiKey)
1290 client.use {
1291 client.connectToServer(args.first())
1292 client.chatLoop()
1293 }
1294}
1295```
1296
1297## Running the client
1298
1299To run your client with any MCP server:
1300
1301```bash theme={null}
1302./gradlew build
1303
1304# Run the client
1305java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.jar # JVM server
1306java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/server.py # Python server
1307java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar path/to/build/index.js # Node server
1308```
1309
1310Alternatively, you can run directly with Gradle:
1311
1312```bash theme={null}
1313./gradlew run --args="path/to/server.jar"
1314```
1315
1316> [!NOTE]
1317>
1318> If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `java -jar build/libs/kotlin-mcp-client-0.1.0-all.jar .../samples/weather-stdio-server/build/libs/weather-stdio-server-0.1.0-all.jar`
1319
1320**The client will:**
1321
13221. Connect to the specified server
13232. List available tools
13243. Start an interactive chat session where you can:
1325 * Enter queries
1326 * See tool executions
1327 * Get responses from Claude
1328
1329## How it works
1330
1331Here's a high-level workflow schema:
1332
1333```mermaid theme={null}
1334---
1335config:
1336 theme: neutral
1337---
1338sequenceDiagram
1339 actor User
1340 participant Client
1341 participant Claude
1342 participant MCP_Server as MCP Server
1343 participant Tools
1344
1345 User->>Client: Send query
1346 Client<<->>MCP_Server: Get available tools
1347 Client->>Claude: Send query with tool descriptions
1348 Claude-->>Client: Decide tool execution
1349 Client->>MCP_Server: Request tool execution
1350 MCP_Server->>Tools: Execute chosen tools
1351 Tools-->>MCP_Server: Return results
1352 MCP_Server-->>Client: Send results
1353 Client->>Claude: Send tool results
1354 Claude-->>Client: Provide final response
1355 Client-->>User: Display response
1356```
1357
1358When you submit a query:
1359
13601. The client gets the list of available tools from the server
13612. Your query is sent to Claude along with tool descriptions
13623. Claude decides which tools (if any) to use
13634. The client executes any requested tool calls through the server
13645. Results are sent back to Claude
13656. Claude provides a natural language response
13667. The response is displayed to you
1367
1368## Best practices
1369
13701. **Error Handling**
1371 * Leverage Kotlin's type system to model errors explicitly
1372 * Wrap external tool and API calls in `try-catch` blocks when exceptions are possible
1373 * Provide clear and meaningful error messages
1374 * Handle network timeouts and connection issues gracefully
1375
13762. **Security**
1377 * Store API keys and secrets securely in `local.properties`, environment variables, or secret managers
1378 * Validate all external responses to avoid unexpected or unsafe data usage
1379 * Be cautious with permissions and trust boundaries when using tools
1380
13813. **Environment**
1382 * Set `ANTHROPIC_API_KEY` through environment variables rather than hardcoding
1383 * Use `.env` files with appropriate `.gitignore` rules for local development
1384
1385## Troubleshooting
1386
1387### Server Path Issues
1388
1389* Double-check the path to your server script is correct
1390* Use the absolute path if the relative path isn't working
1391* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
1392* Make sure that the required runtime is installed (java for Java, npm for Node.js, or uv for Python)
1393* Verify the server file has the correct extension (.jar for Java, .js for Node.js or .py for Python)
1394
1395Example of correct path usage:
1396
1397```bash theme={null}
1398# Relative path
1399java -jar build/libs/client.jar ./server/build/libs/server.jar
1400
1401# Absolute path
1402java -jar build/libs/client.jar /Users/username/projects/mcp-server/build/libs/server.jar
1403
1404# Windows path (either format works)
1405java -jar build/libs/client.jar C:/projects/mcp-server/build/libs/server.jar
1406java -jar build/libs/client.jar C:\\projects\\mcp-server\\build\\libs\\server.jar
1407```
1408
1409### Build Issues
1410
1411* Use `./gradlew build` or `./gradlew shadowJar` (not `./gradlew jar`) to create the shadow JAR with all dependencies
1412* If you get JDK version errors, ensure your installed JDK version matches or exceeds the `jvmToolchain` setting in `build.gradle.kts`
1413
1414### Response Timing
1415
1416* The first response might take up to 30 seconds to return
1417* This is normal and happens while:
1418 * The server initializes
1419 * Claude processes the query
1420 * Tools are being executed
1421* Subsequent responses are typically faster
1422* Don't interrupt the process during this initial waiting period
1423
1424### Common Error Messages
1425
1426If you see:
1427
1428* `Connection refused`: Ensure the server is running and the path is correct
1429* `Tool execution failed`: Verify the tool's required environment variables are set
1430* `ANTHROPIC_API_KEY is not set`: Check your environment variables
1431
1432**C#**
1433
1434[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartClient)
1435
1436## System Requirements
1437
1438Before starting, ensure your system meets these requirements:
1439
1440* .NET 8.0 or higher
1441* Anthropic API key (Claude)
1442* Windows, Linux, or macOS
1443
1444## Setting up your environment
1445
1446First, create a new .NET project:
1447
1448```bash theme={null}
1449dotnet new console -n QuickstartClient
1450cd QuickstartClient
1451```
1452
1453Then, add the required dependencies to your project:
1454
1455```bash theme={null}
1456dotnet add package ModelContextProtocol --prerelease
1457dotnet add package Anthropic.SDK
1458dotnet add package Microsoft.Extensions.Hosting
1459dotnet add package Microsoft.Extensions.AI
1460```
1461
1462## Setting up your API key
1463
1464You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1465
1466```bash theme={null}
1467dotnet user-secrets init
1468dotnet user-secrets set "ANTHROPIC_API_KEY" "<your key here>"
1469```
1470
1471## Creating the Client
1472
1473### Basic Client Structure
1474
1475First, let's setup the basic client class in the file `Program.cs`:
1476
1477```csharp theme={null}
1478using Anthropic.SDK;
1479using Microsoft.Extensions.AI;
1480using Microsoft.Extensions.Configuration;
1481using Microsoft.Extensions.Hosting;
1482using ModelContextProtocol.Client;
1483using ModelContextProtocol.Protocol.Transport;
1484
1485var builder = Host.CreateApplicationBuilder(args);
1486
1487builder.Configuration
1488 .AddEnvironmentVariables()
1489 .AddUserSecrets<Program>();
1490```
1491
1492This creates the beginnings of a .NET console application that can read the API key from user secrets.
1493
1494Next, we'll setup the MCP Client:
1495
1496```csharp theme={null}
1497var (command, arguments) = GetCommandAndArguments(args);
1498
1499var clientTransport = new StdioClientTransport(new()
1500{
1501 Name = "Demo Server",
1502 Command = command,
1503 Arguments = arguments,
1504});
1505
1506await using var mcpClient = await McpClient.CreateAsync(clientTransport);
1507
1508var tools = await mcpClient.ListToolsAsync();
1509foreach (var tool in tools)
1510{
1511 Console.WriteLine($"Connected to server with tools: {tool.Name}");
1512}
1513```
1514
1515Add this function at the end of the `Program.cs` file:
1516
1517```csharp theme={null}
1518static (string command, string[] arguments) GetCommandAndArguments(string[] args)
1519{
1520 return args switch
15081521 {
1509 Name = "Demo Server",
1510 Command = command,
1511 Arguments = arguments,
1512 });
1513
1514 await using var mcpClient = await McpClient.CreateAsync(clientTransport);
1515
1516 var tools = await mcpClient.ListToolsAsync();
1517 foreach (var tool in tools)
1522 [var script] when script.EndsWith(".py") => ("python", args),
1523 [var script] when script.EndsWith(".js") => ("node", args),
1524 [var script] when Directory.Exists(script) || (File.Exists(script) && script.EndsWith(".csproj")) => ("dotnet", ["run", "--project", script, "--no-build"]),
1525 _ => throw new NotSupportedException("An unsupported server script was provided. Supported scripts are .py, .js, or .csproj")
1526 };
1527}
1528```
1529
1530This creates an MCP client that will connect to a server that is provided as a command line argument. It then lists the available tools from the connected server.
1531
1532### Query processing logic
1533
1534Now let's add the core functionality for processing queries and handling tool calls:
1535
1536```csharp theme={null}
1537using var anthropicClient = new AnthropicClient(new APIAuthentication(builder.Configuration["ANTHROPIC_API_KEY"]))
1538 .Messages
1539 .AsBuilder()
1540 .UseFunctionInvocation()
1541 .Build();
1542
1543var options = new ChatOptions
1544{
1545 MaxOutputTokens = 1000,
1546 ModelId = "claude-opus-5",
1547 Tools = [.. tools]
1548};
1549
1550Console.ForegroundColor = ConsoleColor.Green;
1551Console.WriteLine("MCP Client Started!");
1552Console.ResetColor();
1553
1554PromptForInput();
1555while(Console.ReadLine() is string query && !"exit".Equals(query, StringComparison.OrdinalIgnoreCase))
1556{
1557 if (string.IsNullOrWhiteSpace(query))
15181558 {
1519 Console.WriteLine($"Connected to server with tools: {tool.Name}");
1559 PromptForInput();
1560 continue;
15201561 }
1521 ```
1522
1523 Add this function at the end of the `Program.cs` file:
1524
1525 ```csharp theme={null}
1526 static (string command, string[] arguments) GetCommandAndArguments(string[] args)
1562
1563 await foreach (var message in anthropicClient.GetStreamingResponseAsync(query, options))
15271564 {
1528 return args switch
1529 {
1530 [var script] when script.EndsWith(".py") => ("python", args),
1531 [var script] when script.EndsWith(".js") => ("node", args),
1532 [var script] when Directory.Exists(script) || (File.Exists(script) && script.EndsWith(".csproj")) => ("dotnet", ["run", "--project", script, "--no-build"]),
1533 _ => throw new NotSupportedException("An unsupported server script was provided. Supported scripts are .py, .js, or .csproj")
1534 };
1565 Console.Write(message);
15351566 }
1536 ```
1537
1538 This creates an MCP client that will connect to a server that is provided as a command line argument. It then lists the available tools from the connected server.
1539
1540 ### Query processing logic
1541
1542 Now let's add the core functionality for processing queries and handling tool calls:
1543
1544 ```csharp theme={null}
1545 using var anthropicClient = new AnthropicClient(new APIAuthentication(builder.Configuration["ANTHROPIC_API_KEY"]))
1546 .Messages
1547 .AsBuilder()
1548 .UseFunctionInvocation()
1549 .Build();
1550
1551 var options = new ChatOptions
1552 {
1553 MaxOutputTokens = 1000,
1554 ModelId = "claude-opus-5",
1555 Tools = [.. tools]
1556 };
1557
1558 Console.ForegroundColor = ConsoleColor.Green;
1559 Console.WriteLine("MCP Client Started!");
1567 Console.WriteLine();
1568
1569 PromptForInput();
1570}
1571
1572static void PromptForInput()
1573{
1574 Console.WriteLine("Enter a command (or 'exit' to quit):");
1575 Console.ForegroundColor = ConsoleColor.Cyan;
1576 Console.Write("> ");
15601577 Console.ResetColor();
1561
1562 PromptForInput();
1563 while(Console.ReadLine() is string query && !"exit".Equals(query, StringComparison.OrdinalIgnoreCase))
1564 {
1565 if (string.IsNullOrWhiteSpace(query))
1566 {
1567 PromptForInput();
1568 continue;
1569 }
1570
1571 await foreach (var message in anthropicClient.GetStreamingResponseAsync(query, options))
1572 {
1573 Console.Write(message);
1574 }
1575 Console.WriteLine();
1576
1577 PromptForInput();
1578 }
1579
1580 static void PromptForInput()
1581 {
1582 Console.WriteLine("Enter a command (or 'exit' to quit):");
1583 Console.ForegroundColor = ConsoleColor.Cyan;
1584 Console.Write("> ");
1585 Console.ResetColor();
1586 }
1587 ```
1588
1589 ## Key Components Explained
1590
1591 ### 1. Client Initialization
1592
1593 * The client is initialized using `McpClient.CreateAsync()`, which sets up the transport type and command to run the server.
1594
1595 ### 2. Server Connection
1596
1597 * Supports Python, Node.js, and .NET servers.
1598 * The server is started using the command specified in the arguments.
1599 * Configures to use stdio for communication with the server.
1600 * Initializes the session and available tools.
1601
1602 ### 3. Query Processing
1603
1604 * Leverages [Microsoft.Extensions.AI](https://learn.microsoft.com/dotnet/ai/ai-extensions) for the chat client.
1605 * Configures the `IChatClient` to use automatic tool (function) invocation.
1606 * The client reads user input and sends it to the server.
1607 * The server processes the query and returns a response.
1608 * The response is displayed to the user.
1609
1610 ## Running the Client
1611
1612 To run your client with any MCP server:
1613
1614 ```bash theme={null}
1615 dotnet run -- path/to/server.csproj # dotnet server
1616 dotnet run -- path/to/server.py # python server
1617 dotnet run -- path/to/server.js # node server
1618 ```
1619
1620 <Note>
1621 If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `dotnet run -- path/to/QuickstartWeatherServer`.
1622 </Note>
1623
1624 The client will:
1625
1626 1. Connect to the specified server
1627 2. List available tools
1628 3. Start an interactive chat session where you can:
1629 * Enter queries
1630 * See tool executions
1631 * Get responses from Claude
1632 4. Exit the session when done
1633
1634 Here's an example of what it should look like if connected to the weather server quickstart:
1635
1636 <Frame>
1637 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-dotnet-client.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=fcf28dde150d6db879402ad8150c6b23" width="1115" height="666" data-path="images/quickstart-dotnet-client.png" />
1638 </Frame>
1639 </Tab>
1640
1641 <Tab title="Ruby">
1642 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-ruby)
1643
1644 ## System Requirements
1645
1646 Before starting, ensure your system meets these requirements:
1647
1648 * Mac or Windows computer
1649 * Ruby 3.2.0 or higher installed (required by the [Anthropic SDK](https://github.com/anthropics/anthropic-sdk-ruby))
1650 * Anthropic API key (Claude)
1651
1652 ## Setting Up Your Environment
1653
1654 First, create a new Ruby project:
1655
1656 <CodeGroup>
1657 ```bash macOS/Linux theme={null}
1658 # Create project directory
1659 mkdir mcp-client
1660 cd mcp-client
1661
1662 # Create a Gemfile
1663 bundle init
1664
1665 # Add required dependencies
1666 bundle add anthropic base64 dotenv mcp
1667
1668 # Create our main file
1669 touch client.rb
1670 ```
1671
1672 ```powershell Windows theme={null}
1673 # Create project directory
1674 mkdir mcp-client
1675 cd mcp-client
1676
1677 # Create a Gemfile
1678 bundle init
1679
1680 # Add required dependencies
1681 bundle add anthropic base64 dotenv mcp
1682
1683 # Create our main file
1684 new-item client.rb
1685 ```
1686 </CodeGroup>
1687
1688 ## Setting Up Your API Key
1689
1690 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1691
1692 Create a `.env` file to store it:
1693
1694 ```bash theme={null}
1695 echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
1696 ```
1697
1698 Add `.env` to your `.gitignore`:
1699
1700 ```bash theme={null}
1701 echo ".env" >> .gitignore
1702 ```
1703
1704 <Warning>
1705 Make sure you keep your `ANTHROPIC_API_KEY` secure!
1706 </Warning>
1707
1708 ## Creating the Client
1709
1710 ### Basic Client Structure
1711
1712 First, let's set up our requires and create the basic client class:
1713
1714 ```ruby theme={null}
1715 require "anthropic"
1716 require "dotenv/load"
1717 require "json"
1718 require "mcp"
1719
1720 class MCPClient
1721 ANTHROPIC_MODEL = "claude-opus-5"
1722
1723 def initialize
1724 @mcp_client = nil
1725 @transport = nil
1726 @anthropic_client = nil
1727 end
1728
1729 # methods will go here
1730 end
1731 ```
1732
1733 ### Server Connection Management
1734
1735 Next, we'll implement the method to connect to an MCP server:
1736
1737 ```ruby theme={null}
1738 def connect_to_server(server_script_path)
1739 command = case File.extname(server_script_path)
1740 when ".rb"
1741 "ruby"
1742 when ".py"
1743 "python3"
1744 when ".js"
1745 "node"
1746 else
1747 raise ArgumentError, "Server script must be a .rb, .py, or .js file."
1748 end
1749
1750 @transport = MCP::Client::Stdio.new(command: command, args: [server_script_path])
1751 @mcp_client = MCP::Client.new(transport: @transport)
1752 @mcp_client.connect
1753
1754 tool_names = @mcp_client.tools.map(&:name)
1755 puts "\nConnected to server with tools: #{tool_names}"
1756 end
1757 ```
1758
1759 ### Query Processing Logic
1760
1761 Now let's add the core functionality for processing queries and handling tool calls:
1762
1763 ```ruby theme={null}
1764 private
1765
1766 def process_query(query)
1767 messages = [{ role: "user", content: query }]
1768
1769 available_tools = @mcp_client.tools.map do |tool|
1770 { name: tool.name, description: tool.description, input_schema: tool.input_schema }
1771 end
1772
1773 # Initial Claude API call.
1774 response = chat(messages, tools: available_tools)
1775
1776 # Process response and handle tool calls.
1777 if response.content.any?(Anthropic::Models::ToolUseBlock)
1778 assistant_content = response.content.filter_map do |content_block|
1779 case content_block
1780 when Anthropic::Models::TextBlock
1781 { type: "text", text: content_block.text }
1782 when Anthropic::Models::ToolUseBlock
1783 { type: "tool_use", id: content_block.id, name: content_block.name, input: content_block.input }
1784 end
1785 end
1786 messages << { role: "assistant", content: assistant_content }
1787 end
1788
1789 response.content.each_with_object([]) do |content, response_parts|
1790 case content
1791 when Anthropic::Models::TextBlock
1792 response_parts << content.text
1793 when Anthropic::Models::ToolUseBlock
1794 # Execute tool call via MCP.
1795 result = @mcp_client.call_tool(name: content.name, arguments: content.input)
1796 response_parts << "[Calling tool #{content.name} with args #{content.input.to_json}]"
1797
1798 tool_result_content = result.dig("result", "content")
1799 result_text = if tool_result_content.is_a?(Array)
1800 tool_result_content.filter_map { |content_item| content_item["text"] }.join("\n")
1801 else
1802 tool_result_content.to_s
1803 end
1804
1805 messages << {
1806 role: "user",
1807 content: [{
1808 type: "tool_result",
1809 tool_use_id: content.id,
1810 content: result_text
1811 }]
1812 }
1813
1814 # Get next response from Claude.
1815 response = chat(messages)
1816
1817 response.content.each do |content_block|
1818 response_parts << content_block.text if content_block.is_a?(Anthropic::Models::TextBlock)
1819 end
1820 end
1821 end.join("\n")
1822 end
1823
1824 def chat(messages, tools: nil)
1825 params = { model: ANTHROPIC_MODEL, max_tokens: 1000, messages: messages }
1826 params[:tools] = tools if tools
1827
1828 anthropic_client.messages.create(**params)
1829 end
1830
1831 def anthropic_client
1832 @anthropic_client ||= Anthropic::Client.new(api_key: ENV["ANTHROPIC_API_KEY"])
1833 end
1834 ```
1835
1836 ### Interactive Chat Interface
1837
1838 Now we'll add the chat loop and cleanup functionality:
1839
1840 ```ruby theme={null}
1841 def chat_loop
1842 puts <<~MESSAGE
1843 MCP Client Started!
1844 Type your queries or 'quit' to exit.
1845 MESSAGE
1846
1847 loop do
1848 print "\nQuery: "
1849 line = $stdin.gets
1850 break if line.nil?
1851
1852 query = line.chomp.strip
1853 break if query.downcase == "quit"
1854 next if query.empty?
1855
1856 begin
1857 response = process_query(query)
1858 puts "\n#{response}"
1859 rescue => e
1860 puts "\nError: #{e.message}"
1861 end
1578}
1579```
1580
1581## Key Components Explained
1582
1583### 1. Client Initialization
1584
1585* The client is initialized using `McpClient.CreateAsync()`, which sets up the transport type and command to run the server.
1586
1587### 2. Server Connection
1588
1589* Supports Python, Node.js, and .NET servers.
1590* The server is started using the command specified in the arguments.
1591* Configures to use stdio for communication with the server.
1592* Initializes the session and available tools.
1593
1594### 3. Query Processing
1595
1596* Leverages [Microsoft.Extensions.AI](https://learn.microsoft.com/dotnet/ai/ai-extensions) for the chat client.
1597* Configures the `IChatClient` to use automatic tool (function) invocation.
1598* The client reads user input and sends it to the server.
1599* The server processes the query and returns a response.
1600* The response is displayed to the user.
1601
1602## Running the Client
1603
1604To run your client with any MCP server:
1605
1606```bash theme={null}
1607dotnet run -- path/to/server.csproj # dotnet server
1608dotnet run -- path/to/server.py # python server
1609dotnet run -- path/to/server.js # node server
1610```
1611
1612> [!NOTE]
1613>
1614> If you're continuing the weather tutorial from the server quickstart, your command might look something like this: `dotnet run -- path/to/QuickstartWeatherServer`.
1615
1616The client will:
1617
16181. Connect to the specified server
16192. List available tools
16203. Start an interactive chat session where you can:
1621 * Enter queries
1622 * See tool executions
1623 * Get responses from Claude
16244. Exit the session when done
1625
1626Here's an example of what it should look like if connected to the weather server quickstart:
1627
1628
1629
1630**Ruby**
1631
1632[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-ruby)
1633
1634## System Requirements
1635
1636Before starting, ensure your system meets these requirements:
1637
1638* Mac or Windows computer
1639* Ruby 3.2.0 or higher installed (required by the [Anthropic SDK](https://github.com/anthropics/anthropic-sdk-ruby))
1640* Anthropic API key (Claude)
1641
1642## Setting Up Your Environment
1643
1644First, create a new Ruby project:
1645
1646```bash macOS/Linux theme={null}
1647# Create project directory
1648mkdir mcp-client
1649cd mcp-client
1650
1651# Create a Gemfile
1652bundle init
1653
1654# Add required dependencies
1655bundle add anthropic base64 dotenv mcp
1656
1657# Create our main file
1658touch client.rb
1659```
1660
1661```powershell Windows theme={null}
1662# Create project directory
1663mkdir mcp-client
1664cd mcp-client
1665
1666# Create a Gemfile
1667bundle init
1668
1669# Add required dependencies
1670bundle add anthropic base64 dotenv mcp
1671
1672# Create our main file
1673new-item client.rb
1674```
1675
1676## Setting Up Your API Key
1677
1678You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
1679
1680Create a `.env` file to store it:
1681
1682```bash theme={null}
1683echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
1684```
1685
1686Add `.env` to your `.gitignore`:
1687
1688```bash theme={null}
1689echo ".env" >> .gitignore
1690```
1691
1692> [!WARNING]
1693>
1694> Make sure you keep your `ANTHROPIC_API_KEY` secure!
1695
1696## Creating the Client
1697
1698### Basic Client Structure
1699
1700First, let's set up our requires and create the basic client class:
1701
1702```ruby theme={null}
1703require "anthropic"
1704require "dotenv/load"
1705require "json"
1706require "mcp"
1707
1708class MCPClient
1709 ANTHROPIC_MODEL = "claude-opus-5"
1710
1711 def initialize
1712 @mcp_client = nil
1713 @transport = nil
1714 @anthropic_client = nil
1715 end
1716
1717 # methods will go here
1718end
1719```
1720
1721### Server Connection Management
1722
1723Next, we'll implement the method to connect to an MCP server:
1724
1725```ruby theme={null}
1726def connect_to_server(server_script_path)
1727 command = case File.extname(server_script_path)
1728 when ".rb"
1729 "ruby"
1730 when ".py"
1731 "python3"
1732 when ".js"
1733 "node"
1734 else
1735 raise ArgumentError, "Server script must be a .rb, .py, or .js file."
1736 end
1737
1738 @transport = MCP::Client::Stdio.new(command: command, args: [server_script_path])
1739 @mcp_client = MCP::Client.new(transport: @transport)
1740 @mcp_client.connect
1741
1742 tool_names = @mcp_client.tools.map(&:name)
1743 puts "\nConnected to server with tools: #{tool_names}"
1744end
1745```
1746
1747### Query Processing Logic
1748
1749Now let's add the core functionality for processing queries and handling tool calls:
1750
1751```ruby theme={null}
1752private
1753
1754def process_query(query)
1755 messages = [{ role: "user", content: query }]
1756
1757 available_tools = @mcp_client.tools.map do |tool|
1758 { name: tool.name, description: tool.description, input_schema: tool.input_schema }
1759 end
1760
1761 # Initial Claude API call.
1762 response = chat(messages, tools: available_tools)
1763
1764 # Process response and handle tool calls.
1765 if response.content.any?(Anthropic::Models::ToolUseBlock)
1766 assistant_content = response.content.filter_map do |content_block|
1767 case content_block
1768 when Anthropic::Models::TextBlock
1769 { type: "text", text: content_block.text }
1770 when Anthropic::Models::ToolUseBlock
1771 { type: "tool_use", id: content_block.id, name: content_block.name, input: content_block.input }
18621772 end
18631773 end
1864
1865 def cleanup
1866 @transport&.close
1774 messages << { role: "assistant", content: assistant_content }
1775 end
1776
1777 response.content.each_with_object([]) do |content, response_parts|
1778 case content
1779 when Anthropic::Models::TextBlock
1780 response_parts << content.text
1781 when Anthropic::Models::ToolUseBlock
1782 # Execute tool call via MCP.
1783 result = @mcp_client.call_tool(name: content.name, arguments: content.input)
1784 response_parts << "[Calling tool #{content.name} with args #{content.input.to_json}]"
1785
1786 tool_result_content = result.dig("result", "content")
1787 result_text = if tool_result_content.is_a?(Array)
1788 tool_result_content.filter_map { |content_item| content_item["text"] }.join("\n")
1789 else
1790 tool_result_content.to_s
1791 end
1792
1793 messages << {
1794 role: "user",
1795 content: [{
1796 type: "tool_result",
1797 tool_use_id: content.id,
1798 content: result_text
1799 }]
1800 }
1801
1802 # Get next response from Claude.
1803 response = chat(messages)
1804
1805 response.content.each do |content_block|
1806 response_parts << content_block.text if content_block.is_a?(Anthropic::Models::TextBlock)
1807 end
18671808 end
1868 ```
1869
1870 ### Main Entry Point
1871
1872 Finally, we'll add the main execution logic:
1873
1874 ```ruby theme={null}
1875 if ARGV.empty?
1876 puts "Usage: ruby client.rb <path_to_server_script>"
1877 exit 1
1809 end.join("\n")
1810end
1811
1812def chat(messages, tools: nil)
1813 params = { model: ANTHROPIC_MODEL, max_tokens: 1000, messages: messages }
1814 params[:tools] = tools if tools
1815
1816 anthropic_client.messages.create(**params)
1817end
1818
1819def anthropic_client
1820 @anthropic_client ||= Anthropic::Client.new(api_key: ENV["ANTHROPIC_API_KEY"])
1821end
1822```
1823
1824### Interactive Chat Interface
1825
1826Now we'll add the chat loop and cleanup functionality:
1827
1828```ruby theme={null}
1829def chat_loop
1830 puts <<~MESSAGE
1831 MCP Client Started!
1832 Type your queries or 'quit' to exit.
1833 MESSAGE
1834
1835 loop do
1836 print "\nQuery: "
1837 line = $stdin.gets
1838 break if line.nil?
1839
1840 query = line.chomp.strip
1841 break if query.downcase == "quit"
1842 next if query.empty?
1843
1844 begin
1845 response = process_query(query)
1846 puts "\n#{response}"
1847 rescue => e
1848 puts "\nError: #{e.message}"
18781849 end
1879
1880 client = MCPClient.new
1881
1882 begin
1883 client.connect_to_server(ARGV[0])
1884
1885 api_key = ENV["ANTHROPIC_API_KEY"]
1886 if api_key.nil? || api_key.empty?
1887 puts <<~MESSAGE
1888 No ANTHROPIC_API_KEY found. To query these tools with Claude, set your API key:
1889 export ANTHROPIC_API_KEY=your-api-key-here
1890 MESSAGE
1891 exit
1892 end
1893
1894 client.chat_loop
1895 rescue => e
1896 puts "Error: #{e.message}"
1897 exit 1
1898 ensure
1899 client.cleanup
1900 end
1901 ```
1902
1903 You can find the complete `client.rb` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-ruby/client.rb).
1904
1905 ## Key Components Explained
1906
1907 ### 1. Client Initialization
1908
1909 * The `MCPClient` class initializes with nil references for lazy setup
1910 * The Anthropic client is lazily initialized via the `anthropic_client` method
1911 * Uses `dotenv` to load environment variables from `.env`
1912
1913 ### 2. Server Connection
1914
1915 * Supports Ruby, Python, and Node.js servers
1916 * Uses `File.extname` to determine the server script type
1917 * Uses `MCP::Client::Stdio` for stdio transport
1918 * Initializes the MCP client and lists available tools
1919
1920 ### 3. Query Processing
1921
1922 * Maps MCP tools to Anthropic tool format (`name`, `description`, `input_schema`)
1923 * Uses `Anthropic::Models::TextBlock` and `Anthropic::Models::ToolUseBlock` for pattern matching
1924 * Builds assistant content once before iterating tool calls
1925 * Executes tool calls via `@mcp_client.call_tool`
1926 * Uses `chat` helper method to wrap Anthropic API calls
1927 * Extracts tool result content with `result.dig("result", "content")`
1928 * Passes tool results back to Claude for a final response
1929
1930 ### 4. Interactive Interface
1931
1932 * Provides a simple command-line interface
1933 * Handles user input and displays responses
1934 * Skips empty queries
1935 * Includes basic error handling
1936
1937 ### 5. Resource Management
1938
1939 * Proper cleanup of the transport via `begin`...`ensure`
1940 * Top-level `rescue` for error handling
1941 * API key validation after server connection
1942
1943 ## Running the Client
1944
1945 To run your client with any MCP server:
1946
1947 ```bash theme={null}
1948 bundle exec ruby client.rb path/to/server.rb # ruby server
1949 bundle exec ruby client.rb path/to/server.py # python server
1950 bundle exec ruby client.rb path/to/build/index.js # node server
1951 ```
1952
1953 <Note>
1954 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby), your command might look something like this: `bundle exec ruby client.rb /path/to/weather-server-ruby/weather.rb`
1955 </Note>
1956
1957 The client will:
1958
1959 1. Connect to the specified server
1960 2. List available tools
1961 3. Start an interactive chat session where you can:
1962 * Enter queries
1963 * See tool executions
1964 * Get responses from Claude
1965
1966 ## How It Works
1967
1968 When you submit a query:
1969
1970 1. The client gets the list of available tools from the server
1971 2. Your query is sent to Claude along with tool descriptions
1972 3. Claude decides which tools (if any) to use
1973 4. The client executes any requested tool calls through the server
1974 5. Results are sent back to Claude
1975 6. Claude provides a natural language response
1976 7. The response is displayed to you
1977
1978 ## Best practices
1979
1980 1. **Error Handling**
1981 * Wrap tool calls in `begin`...`rescue` blocks
1982 * Provide meaningful error messages
1983 * Gracefully handle connection issues
1984
1985 2. **Resource Management**
1986 * Always close the transport when done
1987 * Use `begin`...`ensure` for proper cleanup
1988 * Handle server disconnections
1989
1990 3. **Security**
1991 * Store API keys securely in `.env`
1992 * Validate server responses
1993 * Be cautious with tool permissions
1994
1995 4. **Tool Names**
1996 * Tool names can be validated according to the format specified [here](/specification/2026-07-28/server/tools#tool-names)
1997 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
1998
1999 ## Troubleshooting
2000
2001 ### Server Path Issues
2002
2003 * Double-check the path to your server script is correct
2004 * Use the absolute path if the relative path isn't working
2005 * For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
2006 * Verify the server file has the correct extension (.py for Python, .js for Node.js, or .rb for Ruby)
2007
2008 Example of correct path usage:
2009
2010 ```bash theme={null}
2011 # Relative path
2012 bundle exec ruby client.rb ./server/weather.rb
2013
2014 # Absolute path
2015 bundle exec ruby client.rb /Users/username/projects/mcp-server/weather.rb
2016
2017 # Windows path (either format works)
2018 bundle exec ruby client.rb C:/projects/mcp-server/weather.rb
2019 bundle exec ruby client.rb C:\\projects\\mcp-server\\weather.rb
2020 ```
2021
2022 ### Response Timing
2023
2024 * The first response might take up to 30 seconds to return
2025 * This is normal and happens while:
2026 * The server initializes
2027 * Claude processes the query
2028 * Tools are being executed
2029 * Subsequent responses are typically faster
2030 * Don't interrupt the process during this initial waiting period
2031
2032 ### Common Error Messages
2033
2034 If you see:
2035
2036 * `Errno::ENOENT`: Check your server path and ensure the command (`ruby`, `python3`, `node`) is available
2037 * `Connection refused`: Ensure the server is running and the path is correct
2038 * `Tool execution failed`: Verify the tool's required environment variables are set
2039 * `Anthropic::Errors::AuthenticationError`: Check your `.env` file has a valid `ANTHROPIC_API_KEY`
2040 </Tab>
2041
2042 <Tab title="Rust">
2043 [You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-rust)
2044
2045 ## System Requirements
2046
2047 Before starting, ensure your Linux system meets these requirements:
2048
2049 * Latest stable version of [Rust and Cargo](https://www.rust-lang.org/tools/install)
2050 * Anthropic API key (Claude)
2051 * A Python, Node.js, or executable MCP server to connect to
2052
2053 ## Setting Up Your Environment
2054
2055 First, create a new Rust project:
2056
2057 ```bash theme={null}
2058 cargo new mcp-client-rust
2059 cd mcp-client-rust
2060 ```
2061
2062 Replace the contents of `Cargo.toml` with the following:
2063
2064 ```toml Cargo.toml theme={null}
2065 [package]
2066 name = "mcp-client-rust"
2067 version = "0.1.0"
2068 edition = "2024"
2069
2070 [dependencies]
2071 anyhow = "1.0.100"
2072 genai = "0.4.2"
2073 rmcp = { version = "0.8.0", features = ["server", "client", "transport-io", "transport-child-process"] }
2074 tokio = { version = "1.47.1", features = ["full"] }
2075 tracing = "0.1.41"
2076 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
2077 serde_json = "1.0.128"
2078 dotenvy = "0.15.7"
2079 reqwest = "0.12.23"
2080 ```
2081
2082 The [`rmcp`](https://github.com/modelcontextprotocol/rust-sdk) crate provides the Rust MCP SDK and child-process transport. This example uses the [`genai`](https://github.com/jeremychone/rust-genai) crate to send requests to Claude and represent tools in the model request.
2083
2084 ## Setting Up Your API Key
2085
2086 You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
2087
2088 Create a `.env` file to store it:
2089
2090 ```bash theme={null}
2091 echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
2092 ```
2093
2094 Add `.env` to your `.gitignore`:
2095
2096 ```bash theme={null}
2097 echo ".env" >> .gitignore
2098 ```
2099
2100 <Warning>
2101 Make sure you keep your `ANTHROPIC_API_KEY` secure!
2102 </Warning>
2103
2104 ## Creating the Client
2105
2106 Open `src/main.rs` and replace its contents as you work through the following sections.
2107
2108 ### Imports and Client Structure
2109
2110 First, add the imports, model constant, and basic client structure:
2111
2112 ```rust theme={null}
2113 use anyhow::{Context, Result, bail};
2114 use genai::Client;
2115 use genai::chat::{
2116 ChatMessage, ChatRequest, ChatResponse, ContentPart, Tool as GenaiTool, ToolResponse,
2117 };
2118 use rmcp::model::{CallToolRequestParam, Tool as McpTool};
2119 use rmcp::service::{RoleClient, RunningService, ServiceExt};
2120 use rmcp::transport::TokioChildProcess;
2121 use serde_json::Value;
2122 use tokio::io::{self, AsyncBufReadExt, BufReader};
2123 use tokio::process::Command;
2124
2125 const MODEL_ANTHROPIC: &str = "claude-opus-5";
2126
2127 struct MCPClient {
2128 anthropic: Client,
2129 session: Option<RunningService<RoleClient, ()>>,
2130 tools: Vec<GenaiTool>,
1850 end
1851end
1852
1853def cleanup
1854 @transport&.close
1855end
1856```
1857
1858### Main Entry Point
1859
1860Finally, we'll add the main execution logic:
1861
1862```ruby theme={null}
1863if ARGV.empty?
1864 puts "Usage: ruby client.rb <path_to_server_script>"
1865 exit 1
1866end
1867
1868client = MCPClient.new
1869
1870begin
1871 client.connect_to_server(ARGV[0])
1872
1873 api_key = ENV["ANTHROPIC_API_KEY"]
1874 if api_key.nil? || api_key.empty?
1875 puts <<~MESSAGE
1876 No ANTHROPIC_API_KEY found. To query these tools with Claude, set your API key:
1877 export ANTHROPIC_API_KEY=your-api-key-here
1878 MESSAGE
1879 exit
1880 end
1881
1882 client.chat_loop
1883rescue => e
1884 puts "Error: #{e.message}"
1885 exit 1
1886ensure
1887 client.cleanup
1888end
1889```
1890
1891You can find the complete `client.rb` file [here](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-ruby/client.rb).
1892
1893## Key Components Explained
1894
1895### 1. Client Initialization
1896
1897* The `MCPClient` class initializes with nil references for lazy setup
1898* The Anthropic client is lazily initialized via the `anthropic_client` method
1899* Uses `dotenv` to load environment variables from `.env`
1900
1901### 2. Server Connection
1902
1903* Supports Ruby, Python, and Node.js servers
1904* Uses `File.extname` to determine the server script type
1905* Uses `MCP::Client::Stdio` for stdio transport
1906* Initializes the MCP client and lists available tools
1907
1908### 3. Query Processing
1909
1910* Maps MCP tools to Anthropic tool format (`name`, `description`, `input_schema`)
1911* Uses `Anthropic::Models::TextBlock` and `Anthropic::Models::ToolUseBlock` for pattern matching
1912* Builds assistant content once before iterating tool calls
1913* Executes tool calls via `@mcp_client.call_tool`
1914* Uses `chat` helper method to wrap Anthropic API calls
1915* Extracts tool result content with `result.dig("result", "content")`
1916* Passes tool results back to Claude for a final response
1917
1918### 4. Interactive Interface
1919
1920* Provides a simple command-line interface
1921* Handles user input and displays responses
1922* Skips empty queries
1923* Includes basic error handling
1924
1925### 5. Resource Management
1926
1927* Proper cleanup of the transport via `begin`...`ensure`
1928* Top-level `rescue` for error handling
1929* API key validation after server connection
1930
1931## Running the Client
1932
1933To run your client with any MCP server:
1934
1935```bash theme={null}
1936bundle exec ruby client.rb path/to/server.rb # ruby server
1937bundle exec ruby client.rb path/to/server.py # python server
1938bundle exec ruby client.rb path/to/build/index.js # node server
1939```
1940
1941> [!NOTE]
1942>
1943> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby), your command might look something like this: `bundle exec ruby client.rb /path/to/weather-server-ruby/weather.rb`
1944
1945The client will:
1946
19471. Connect to the specified server
19482. List available tools
19493. Start an interactive chat session where you can:
1950 * Enter queries
1951 * See tool executions
1952 * Get responses from Claude
1953
1954## How It Works
1955
1956When you submit a query:
1957
19581. The client gets the list of available tools from the server
19592. Your query is sent to Claude along with tool descriptions
19603. Claude decides which tools (if any) to use
19614. The client executes any requested tool calls through the server
19625. Results are sent back to Claude
19636. Claude provides a natural language response
19647. The response is displayed to you
1965
1966## Best practices
1967
19681. **Error Handling**
1969 * Wrap tool calls in `begin`...`rescue` blocks
1970 * Provide meaningful error messages
1971 * Gracefully handle connection issues
1972
19732. **Resource Management**
1974 * Always close the transport when done
1975 * Use `begin`...`ensure` for proper cleanup
1976 * Handle server disconnections
1977
19783. **Security**
1979 * Store API keys securely in `.env`
1980 * Validate server responses
1981 * Be cautious with tool permissions
1982
19834. **Tool Names**
1984 * Tool names can be validated according to the format specified [here](/specification/2026-07-28/server/tools#tool-names)
1985 * If a tool name conforms to the specified format, it should not fail validation by an MCP client
1986
1987## Troubleshooting
1988
1989### Server Path Issues
1990
1991* Double-check the path to your server script is correct
1992* Use the absolute path if the relative path isn't working
1993* For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
1994* Verify the server file has the correct extension (.py for Python, .js for Node.js, or .rb for Ruby)
1995
1996Example of correct path usage:
1997
1998```bash theme={null}
1999# Relative path
2000bundle exec ruby client.rb ./server/weather.rb
2001
2002# Absolute path
2003bundle exec ruby client.rb /Users/username/projects/mcp-server/weather.rb
2004
2005# Windows path (either format works)
2006bundle exec ruby client.rb C:/projects/mcp-server/weather.rb
2007bundle exec ruby client.rb C:\\projects\\mcp-server\\weather.rb
2008```
2009
2010### Response Timing
2011
2012* The first response might take up to 30 seconds to return
2013* This is normal and happens while:
2014 * The server initializes
2015 * Claude processes the query
2016 * Tools are being executed
2017* Subsequent responses are typically faster
2018* Don't interrupt the process during this initial waiting period
2019
2020### Common Error Messages
2021
2022If you see:
2023
2024* `Errno::ENOENT`: Check your server path and ensure the command (`ruby`, `python3`, `node`) is available
2025* `Connection refused`: Ensure the server is running and the path is correct
2026* `Tool execution failed`: Verify the tool's required environment variables are set
2027* `Anthropic::Errors::AuthenticationError`: Check your `.env` file has a valid `ANTHROPIC_API_KEY`
2028
2029**Rust**
2030
2031[You can find the complete code for this tutorial here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/mcp-client-rust)
2032
2033## System Requirements
2034
2035Before starting, ensure your Linux system meets these requirements:
2036
2037* Latest stable version of [Rust and Cargo](https://www.rust-lang.org/tools/install)
2038* Anthropic API key (Claude)
2039* A Python, Node.js, or executable MCP server to connect to
2040
2041## Setting Up Your Environment
2042
2043First, create a new Rust project:
2044
2045```bash theme={null}
2046cargo new mcp-client-rust
2047cd mcp-client-rust
2048```
2049
2050Replace the contents of `Cargo.toml` with the following:
2051
2052```toml Cargo.toml theme={null}
2053[package]
2054name = "mcp-client-rust"
2055version = "0.1.0"
2056edition = "2024"
2057
2058[dependencies]
2059anyhow = "1.0.100"
2060genai = "0.4.2"
2061rmcp = { version = "0.8.0", features = ["server", "client", "transport-io", "transport-child-process"] }
2062tokio = { version = "1.47.1", features = ["full"] }
2063tracing = "0.1.41"
2064tracing-subscriber = { version = "0.3", features = ["env-filter"] }
2065serde_json = "1.0.128"
2066dotenvy = "0.15.7"
2067reqwest = "0.12.23"
2068```
2069
2070The [`rmcp`](https://github.com/modelcontextprotocol/rust-sdk) crate provides the Rust MCP SDK and child-process transport. This example uses the [`genai`](https://github.com/jeremychone/rust-genai) crate to send requests to Claude and represent tools in the model request.
2071
2072## Setting Up Your API Key
2073
2074You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
2075
2076Create a `.env` file to store it:
2077
2078```bash theme={null}
2079echo "ANTHROPIC_API_KEY=your-api-key-goes-here" > .env
2080```
2081
2082Add `.env` to your `.gitignore`:
2083
2084```bash theme={null}
2085echo ".env" >> .gitignore
2086```
2087
2088> [!WARNING]
2089>
2090> Make sure you keep your `ANTHROPIC_API_KEY` secure!
2091
2092## Creating the Client
2093
2094Open `src/main.rs` and replace its contents as you work through the following sections.
2095
2096### Imports and Client Structure
2097
2098First, add the imports, model constant, and basic client structure:
2099
2100```rust theme={null}
2101use anyhow::{Context, Result, bail};
2102use genai::Client;
2103use genai::chat::{
2104 ChatMessage, ChatRequest, ChatResponse, ContentPart, Tool as GenaiTool, ToolResponse,
2105};
2106use rmcp::model::{CallToolRequestParam, Tool as McpTool};
2107use rmcp::service::{RoleClient, RunningService, ServiceExt};
2108use rmcp::transport::TokioChildProcess;
2109use serde_json::Value;
2110use tokio::io::{self, AsyncBufReadExt, BufReader};
2111use tokio::process::Command;
2112
2113const MODEL_ANTHROPIC: &str = "claude-opus-5";
2114
2115struct MCPClient {
2116 anthropic: Client,
2117 session: Option<RunningService<RoleClient, ()>>,
2118 tools: Vec<GenaiTool>,
2119}
2120```
2121
2122The client keeps the model API client, the active MCP session, and the tools advertised by the connected server.
2123
2124### Client Initialization
2125
2126Next, initialize the model client and start without an MCP session or tools:
2127
2128```rust theme={null}
2129impl MCPClient {
2130 fn new() -> Result<Self> {
2131 Ok(MCPClient {
2132 anthropic: Client::default(),
2133 session: None,
2134 tools: Vec::new(),
2135 })
21312136 }
2132 ```
2133
2134 The client keeps the model API client, the active MCP session, and the tools advertised by the connected server.
2135
2136 ### Client Initialization
2137
2138 Next, initialize the model client and start without an MCP session or tools:
2139
2140 ```rust theme={null}
2141 impl MCPClient {
2142 fn new() -> Result<Self> {
2143 Ok(MCPClient {
2144 anthropic: Client::default(),
2145 session: None,
2146 tools: Vec::new(),
2147 })
2137
2138 // Additional methods will go here.
2139}
2140```
2141
2142`genai::Client::default()` reads the `ANTHROPIC_API_KEY` environment variable when it sends a request.
2143
2144### Server Connection Management
2145
2146Add this method inside the `impl MCPClient` block:
2147
2148```rust theme={null}
2149async fn connect_to_server(&mut self, server_args: &[String]) -> Result<()> {
2150 if self.session.is_some() {
2151 bail!("Client is already connected to a server");
2152 }
2153
2154 let mut command = Command::new(&server_args[0]);
2155 command.args(&server_args[1..]);
2156
2157 let process = TokioChildProcess::new(command)
2158 .with_context(|| format!("Failed to spawn server process for {:?}", server_args))?;
2159
2160 let session = ().serve(process).await?;
2161
2162 let rmcp_tools = session
2163 .list_all_tools()
2164 .await
2165 .context("Unable to list tools from server")?;
2166
2167 let tool_names: Vec<String> = rmcp_tools
2168 .iter()
2169 .map(|tool| tool.name.to_string())
2170 .collect();
2171
2172 println!("Connected to server with tools: {tool_names:?}");
2173
2174 self.tools = convert_tools(&rmcp_tools);
2175 self.session = Some(session);
2176 Ok(())
2177}
2178```
2179
2180This method:
2181
21821. Starts the server as a child process using the command and arguments supplied on the command line
21832. Establishes an MCP session over stdio
21843. Lists all tools advertised by the server
21854. Converts those tools into the format used in model requests
2186
2187### Converting MCP Tools
2188
2189Add this function outside the `impl MCPClient` block:
2190
2191```rust theme={null}
2192fn convert_tools(tools: &[McpTool]) -> Vec<GenaiTool> {
2193 tools
2194 .iter()
2195 .map(|tool| GenaiTool {
2196 name: tool.name.to_string(),
2197 description: tool.description.as_deref().map(str::to_string),
2198 schema: Some(Value::Object(tool.input_schema.as_ref().clone())),
2199 config: None,
2200 })
2201 .collect()
2202}
2203```
2204
2205MCP and model APIs describe tools with similar information but different Rust types. `convert_tools` maps each MCP tool's name, description, and input schema into a `genai` tool definition.
2206
2207### Sending Model Requests
2208
2209Add this helper method inside `impl MCPClient`:
2210
2211```rust theme={null}
2212async fn request_model(&self, chat_req: &ChatRequest) -> Result<ChatResponse> {
2213 let response = self
2214 .anthropic
2215 .exec_chat(MODEL_ANTHROPIC, chat_req.clone(), None)
2216 .await
2217 .context("Anthropic chat request failed")?;
2218
2219 Ok(response)
2220}
2221```
2222
2223This keeps model request handling in one place and adds useful context if the API request fails.
2224
2225### Query Processing Logic
2226
2227Now add the core query-processing method inside `impl MCPClient`:
2228
2229```rust theme={null}
2230async fn process_query(&mut self, query: &str) -> Result<String> {
2231 let session = self
2232 .session
2233 .as_ref()
2234 .context("Client is not connected to any server")?;
2235
2236 let mut messages = vec![ChatMessage::user(query)];
2237 let mut final_text = Vec::new();
2238
2239 // Initial Claude API call with tools
2240 let mut chat_req = ChatRequest::new(messages.clone()).with_tools(self.tools.clone());
2241 let mut chat_rsp = self.request_model(&chat_req).await?;
2242
2243 // Process response content - collect text and handle tool calls
2244 for text in chat_rsp.texts() {
2245 final_text.push(text.to_string());
2246 }
2247
2248 let tool_calls = chat_rsp.tool_calls();
2249 if !tool_calls.is_empty() {
2250 // Append assistant's response to message history
2251 messages.push(ChatMessage::assistant(chat_rsp.content.clone()));
2252
2253 // Execute each tool call and collect responses
2254 let mut tool_results = Vec::new();
2255 for tool_call in tool_calls {
2256 // Add information about the tool call to final text
2257 let tool_args_str = serde_json::to_string(&tool_call.fn_arguments)
2258 .unwrap_or_else(|_| "{}".to_string());
2259
2260 final_text.push(format!(
2261 "[Calling tool {} with args {}]",
2262 tool_call.fn_name, tool_args_str
2263 ));
2264
2265 // Query the MCP server
2266 let tool_result = session
2267 .call_tool(CallToolRequestParam {
2268 name: tool_call.fn_name.clone().into(),
2269 arguments: tool_call.fn_arguments.as_object().cloned(),
2270 })
2271 .await
2272 .with_context(|| format!("Tool call {} failed", tool_call.fn_name))?;
2273
2274 let payload = serde_json::to_string(&tool_result)
2275 .context("Failed to serialize tool result")?;
2276
2277 tool_results.push(ContentPart::ToolResponse(ToolResponse::new(
2278 tool_call.call_id.clone(),
2279 payload,
2280 )));
21482281 }
21492282
2150 // Additional methods will go here.
2151 }
2152 ```
2153
2154 `genai::Client::default()` reads the `ANTHROPIC_API_KEY` environment variable when it sends a request.
2155
2156 ### Server Connection Management
2157
2158 Add this method inside the `impl MCPClient` block:
2159
2160 ```rust theme={null}
2161 async fn connect_to_server(&mut self, server_args: &[String]) -> Result<()> {
2162 if self.session.is_some() {
2163 bail!("Client is already connected to a server");
2164 }
2165
2166 let mut command = Command::new(&server_args[0]);
2167 command.args(&server_args[1..]);
2168
2169 let process = TokioChildProcess::new(command)
2170 .with_context(|| format!("Failed to spawn server process for {:?}", server_args))?;
2171
2172 let session = ().serve(process).await?;
2173
2174 let rmcp_tools = session
2175 .list_all_tools()
2176 .await
2177 .context("Unable to list tools from server")?;
2178
2179 let tool_names: Vec<String> = rmcp_tools
2180 .iter()
2181 .map(|tool| tool.name.to_string())
2182 .collect();
2183
2184 println!("Connected to server with tools: {tool_names:?}");
2185
2186 self.tools = convert_tools(&rmcp_tools);
2187 self.session = Some(session);
2188 Ok(())
2189 }
2190 ```
2191
2192 This method:
2193
2194 1. Starts the server as a child process using the command and arguments supplied on the command line
2195 2. Establishes an MCP session over stdio
2196 3. Lists all tools advertised by the server
2197 4. Converts those tools into the format used in model requests
2198
2199 ### Converting MCP Tools
2200
2201 Add this function outside the `impl MCPClient` block:
2202
2203 ```rust theme={null}
2204 fn convert_tools(tools: &[McpTool]) -> Vec<GenaiTool> {
2205 tools
2206 .iter()
2207 .map(|tool| GenaiTool {
2208 name: tool.name.to_string(),
2209 description: tool.description.as_deref().map(str::to_string),
2210 schema: Some(Value::Object(tool.input_schema.as_ref().clone())),
2211 config: None,
2212 })
2213 .collect()
2214 }
2215 ```
2216
2217 MCP and model APIs describe tools with similar information but different Rust types. `convert_tools` maps each MCP tool's name, description, and input schema into a `genai` tool definition.
2218
2219 ### Sending Model Requests
2220
2221 Add this helper method inside `impl MCPClient`:
2222
2223 ```rust theme={null}
2224 async fn request_model(&self, chat_req: &ChatRequest) -> Result<ChatResponse> {
2225 let response = self
2226 .anthropic
2227 .exec_chat(MODEL_ANTHROPIC, chat_req.clone(), None)
2228 .await
2229 .context("Anthropic chat request failed")?;
2230
2231 Ok(response)
2232 }
2233 ```
2234
2235 This keeps model request handling in one place and adds useful context if the API request fails.
2236
2237 ### Query Processing Logic
2238
2239 Now add the core query-processing method inside `impl MCPClient`:
2240
2241 ```rust theme={null}
2242 async fn process_query(&mut self, query: &str) -> Result<String> {
2243 let session = self
2244 .session
2245 .as_ref()
2246 .context("Client is not connected to any server")?;
2247
2248 let mut messages = vec![ChatMessage::user(query)];
2249 let mut final_text = Vec::new();
2250
2251 // Initial Claude API call with tools
2252 let mut chat_req = ChatRequest::new(messages.clone()).with_tools(self.tools.clone());
2253 let mut chat_rsp = self.request_model(&chat_req).await?;
2254
2255 // Process response content - collect text and handle tool calls
2283 // Append tool responses to message history
2284 messages.push(ChatMessage::user(tool_results));
2285
2286 // Build the next request and query model
2287 chat_req = ChatRequest::new(messages.clone());
2288 chat_rsp = self.request_model(&chat_req).await?;
2289
2290 // Collect text from response
22562291 for text in chat_rsp.texts() {
22572292 final_text.push(text.to_string());
22582293 }
2259
2260 let tool_calls = chat_rsp.tool_calls();
2261 if !tool_calls.is_empty() {
2262 // Append assistant's response to message history
2263 messages.push(ChatMessage::assistant(chat_rsp.content.clone()));
2264
2265 // Execute each tool call and collect responses
2266 let mut tool_results = Vec::new();
2267 for tool_call in tool_calls {
2268 // Add information about the tool call to final text
2269 let tool_args_str = serde_json::to_string(&tool_call.fn_arguments)
2270 .unwrap_or_else(|_| "{}".to_string());
2271
2272 final_text.push(format!(
2273 "[Calling tool {} with args {}]",
2274 tool_call.fn_name, tool_args_str
2275 ));
2276
2277 // Query the MCP server
2278 let tool_result = session
2279 .call_tool(CallToolRequestParam {
2280 name: tool_call.fn_name.clone().into(),
2281 arguments: tool_call.fn_arguments.as_object().cloned(),
2282 })
2283 .await
2284 .with_context(|| format!("Tool call {} failed", tool_call.fn_name))?;
2285
2286 let payload = serde_json::to_string(&tool_result)
2287 .context("Failed to serialize tool result")?;
2288
2289 tool_results.push(ContentPart::ToolResponse(ToolResponse::new(
2290 tool_call.call_id.clone(),
2291 payload,
2292 )));
2293 }
2294
2295 // Append tool responses to message history
2296 messages.push(ChatMessage::user(tool_results));
2297
2298 // Build the next request and query model
2299 chat_req = ChatRequest::new(messages.clone());
2300 chat_rsp = self.request_model(&chat_req).await?;
2301
2302 // Collect text from response
2303 for text in chat_rsp.texts() {
2304 final_text.push(text.to_string());
2305 }
2294 }
2295
2296 Ok(final_text.join("\n"))
2297}
2298```
2299
2300The method first sends the user's query and available tools to Claude. When Claude requests tools, the client executes each request through the MCP session, sends the results back to Claude, and collects the final text response.
2301
2302### Interactive Chat Interface
2303
2304Add the interactive terminal loop inside `impl MCPClient`:
2305
2306```rust theme={null}
2307async fn chat_loop(&mut self) -> Result<()> {
2308 println!("\nMCP Client Started!");
2309 println!("Type your queries or 'quit' to exit.");
2310
2311 let mut stdin = BufReader::new(io::stdin());
2312 let mut input = String::new();
2313
2314 loop {
2315 print!("\nQuery: ");
2316 std::io::Write::flush(&mut std::io::stdout())?;
2317
2318 input.clear();
2319 if stdin.read_line(&mut input).await? == 0 {
2320 break; // EOF
23062321 }
23072322
2308 Ok(final_text.join("\n"))
2323 let query = input.trim();
2324 if query.eq_ignore_ascii_case("quit") {
2325 break;
2326 }
2327 if query.is_empty() {
2328 continue;
2329 }
2330
2331 match self.process_query(query).await {
2332 Ok(response) => println!("\n{}", response),
2333 Err(err) => println!("\nError: {}", err),
2334 }
23092335 }
2310 ```
2311
2312 The method first sends the user's query and available tools to Claude. When Claude requests tools, the client executes each request through the MCP session, sends the results back to Claude, and collects the final text response.
2313
2314 ### Interactive Chat Interface
2315
2316 Add the interactive terminal loop inside `impl MCPClient`:
2317
2318 ```rust theme={null}
2319 async fn chat_loop(&mut self) -> Result<()> {
2320 println!("\nMCP Client Started!");
2321 println!("Type your queries or 'quit' to exit.");
2322
2323 let mut stdin = BufReader::new(io::stdin());
2324 let mut input = String::new();
2325
2326 loop {
2327 print!("\nQuery: ");
2328 std::io::Write::flush(&mut std::io::stdout())?;
2329
2330 input.clear();
2331 if stdin.read_line(&mut input).await? == 0 {
2332 break; // EOF
2333 }
2334
2335 let query = input.trim();
2336 if query.eq_ignore_ascii_case("quit") {
2337 break;
2338 }
2339 if query.is_empty() {
2340 continue;
2341 }
2342
2343 match self.process_query(query).await {
2344 Ok(response) => println!("\n{}", response),
2345 Err(err) => println!("\nError: {}", err),
2346 }
2347 }
2348
2349 Ok(())
2336
2337 Ok(())
2338}
2339```
2340
2341The loop accepts queries until the user types `quit` or closes standard input. Query errors are printed without terminating the client.
2342
2343### Cleanup
2344
2345Add this method inside `impl MCPClient` to stop the MCP session and child process:
2346
2347```rust theme={null}
2348async fn cleanup(&mut self) -> Result<()> {
2349 if let Some(session) = self.session.take() {
2350 let _ = session.cancel().await;
23502351 }
2351 ```
2352
2353 The loop accepts queries until the user types `quit` or closes standard input. Query errors are printed without terminating the client.
2354
2355 ### Cleanup
2356
2357 Add this method inside `impl MCPClient` to stop the MCP session and child process:
2358
2359 ```rust theme={null}
2360 async fn cleanup(&mut self) -> Result<()> {
2361 if let Some(session) = self.session.take() {
2362 let _ = session.cancel().await;
2363 }
2364 Ok(())
2352 Ok(())
2353}
2354```
2355
2356### Main Entry Point
2357
2358Finally, add the asynchronous entry point outside the `impl MCPClient` block:
2359
2360```rust theme={null}
2361#[tokio::main]
2362async fn main() -> Result<()> {
2363 dotenvy::dotenv().context("Failed to load env file")?;
2364
2365 let mut args = std::env::args();
2366 let _ = args.next();
2367 let server_args: Vec<String> = args.collect();
2368
2369 if server_args.is_empty() {
2370 eprintln!("Usage: cargo run -- <server_script_or_binary> [args...]");
2371 std::process::exit(1);
23652372 }
2366 ```
2367
2368 ### Main Entry Point
2369
2370 Finally, add the asynchronous entry point outside the `impl MCPClient` block:
2371
2372 ```rust theme={null}
2373 #[tokio::main]
2374 async fn main() -> Result<()> {
2375 dotenvy::dotenv().context("Failed to load env file")?;
2376
2377 let mut args = std::env::args();
2378 let _ = args.next();
2379 let server_args: Vec<String> = args.collect();
2380
2381 if server_args.is_empty() {
2382 eprintln!("Usage: cargo run -- <server_script_or_binary> [args...]");
2383 std::process::exit(1);
2384 }
2385
2386 let mut client = MCPClient::new()?;
2387
2388 let result = async {
2389 client.connect_to_server(&server_args).await?;
2390 client.chat_loop().await
2391 }
2392 .await;
2393
2394 let cleanup_result = client.cleanup().await;
2395
2396 result?;
2397 cleanup_result?;
2398
2399 Ok(())
2373
2374 let mut client = MCPClient::new()?;
2375
2376 let result = async {
2377 client.connect_to_server(&server_args).await?;
2378 client.chat_loop().await
24002379 }
2401 ```
2402
2403 The entry point loads `.env`, treats all remaining command-line arguments as the server command, connects the client, starts the chat loop, and ensures cleanup runs before exiting.
2404
2405 ### Verify the Complete File
2406
2407 Before running the client, confirm the items in `src/main.rs` are placed at the correct scope:
2408
2409 * `new`, `connect_to_server`, `process_query`, `request_model`, `chat_loop`, and `cleanup` are methods inside the single `impl MCPClient` block.
2410 * `main` and `convert_tools` are functions outside the `impl MCPClient` block.
2411
2412 Rust does not require these items to appear in a particular order, but methods and free functions must be placed in the correct scope. Compare your file with the [complete `src/main.rs` example](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-rust/src/main.rs), then check that it compiles:
2413
2414 ```bash theme={null}
2415 cargo fmt --check
2416 cargo check
2417 ```
2418
2419 ## Running the Client
2420
2421 Use `cargo run --` followed by the command you would normally use to start the MCP server:
2422
2423 ```bash theme={null}
2424 # Python server
2425 cargo run -- python path/to/server.py
2426
2427 # Node.js server
2428 cargo run -- node path/to/build/index.js
2429
2430 # Executable server
2431 cargo run -- path/to/server-binary
2432 ```
2433
2434 Running bare `cargo run` without a server command prints the usage message and exits.
2435
2436 <Note>
2437 If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust), build the server first and then run a command similar to: `cargo run -- ../weather-server-rust/target/debug/weather`
2438 </Note>
2439
2440 The client will:
2441
2442 1. Start and connect to the specified MCP server
2443 2. List the tools available from that server
2444 3. Start an interactive chat session where you can:
2445 * Enter queries
2446 * See tool executions
2447 * Get responses from Claude
2448
2449 ## How It Works
2450
2451 When you submit a query:
2452
2453 1. The client sends your query and the server's available tools to Claude
2454 2. Claude decides which tools, if any, to use
2455 3. The client executes requested tools through the MCP session
2456 4. Tool results are sent back to Claude
2457 5. Claude provides a natural language response
2458 6. The response is displayed in the terminal
2459
2460 ## Best Practices
2461
2462 1. **Error Handling**
2463 * Add context to errors at process, MCP, model API, and serialization boundaries
2464 * Report individual query errors without terminating the interactive session
2465 * Validate server commands before running them
2466
2467 2. **Resource Management**
2468 * Always cancel the MCP session during cleanup
2469 * Ensure cleanup runs even when connection or chat-loop operations fail
2470 * Avoid starting a second server while a session is active
2471
2472 3. **Security**
2473 * Store API keys securely in `.env`
2474 * Review the tools exposed by a server before allowing model-driven calls
2475 * Connect only to servers and executable commands you trust
2476
2477 ## Troubleshooting
2478
2479 ### Server Command Issues
2480
2481 The arguments after `cargo run --` must form a complete command. Interpreted server scripts need their runtime:
2482
2483 ```bash theme={null}
2484 # Correct
2485 cargo run -- python ./server/weather.py
2486 cargo run -- node ./server/build/index.js
2487
2488 # Incorrect: a Python script is not necessarily executable by itself
2489 cargo run -- ./server/weather.py
2490 ```
2491
2492 If a command cannot be found, use its absolute path or verify it is available in your `PATH`.
2493
2494 ### Environment File Issues
2495
2496 If you see `Failed to load env file`, ensure `.env` exists in the directory where you run the client.
2497
2498 If the model request reports a missing API key, confirm that `.env` contains:
2499
2500 ```text theme={null}
2501 ANTHROPIC_API_KEY=your-api-key-goes-here
2502 ```
2503
2504 ### Tool and Response Errors
2505
2506 * `Unable to list tools from server`: Verify the server starts successfully and communicates over stdio
2507 * `Tool call ... failed`: Verify the server tool's required arguments and environment variables
2508 * `Failed to serialize tool result`: Inspect the server's response for unsupported or malformed content
2509 </Tab>
2510</Tabs>
2380 .await;
2381
2382 let cleanup_result = client.cleanup().await;
2383
2384 result?;
2385 cleanup_result?;
2386
2387 Ok(())
2388}
2389```
2390
2391The entry point loads `.env`, treats all remaining command-line arguments as the server command, connects the client, starts the chat loop, and ensures cleanup runs before exiting.
2392
2393### Verify the Complete File
2394
2395Before running the client, confirm the items in `src/main.rs` are placed at the correct scope:
2396
2397* `new`, `connect_to_server`, `process_query`, `request_model`, `chat_loop`, and `cleanup` are methods inside the single `impl MCPClient` block.
2398* `main` and `convert_tools` are functions outside the `impl MCPClient` block.
2399
2400Rust does not require these items to appear in a particular order, but methods and free functions must be placed in the correct scope. Compare your file with the [complete `src/main.rs` example](https://github.com/modelcontextprotocol/quickstart-resources/blob/main/mcp-client-rust/src/main.rs), then check that it compiles:
2401
2402```bash theme={null}
2403cargo fmt --check
2404cargo check
2405```
2406
2407## Running the Client
2408
2409Use `cargo run --` followed by the command you would normally use to start the MCP server:
2410
2411```bash theme={null}
2412# Python server
2413cargo run -- python path/to/server.py
2414
2415# Node.js server
2416cargo run -- node path/to/build/index.js
2417
2418# Executable server
2419cargo run -- path/to/server-binary
2420```
2421
2422Running bare `cargo run` without a server command prints the usage message and exits.
2423
2424> [!NOTE]
2425>
2426> If you're continuing [the weather tutorial from the server quickstart](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust), build the server first and then run a command similar to: `cargo run -- ../weather-server-rust/target/debug/weather`
2427
2428The client will:
2429
24301. Start and connect to the specified MCP server
24312. List the tools available from that server
24323. Start an interactive chat session where you can:
2433 * Enter queries
2434 * See tool executions
2435 * Get responses from Claude
2436
2437## How It Works
2438
2439When you submit a query:
2440
24411. The client sends your query and the server's available tools to Claude
24422. Claude decides which tools, if any, to use
24433. The client executes requested tools through the MCP session
24444. Tool results are sent back to Claude
24455. Claude provides a natural language response
24466. The response is displayed in the terminal
2447
2448## Best Practices
2449
24501. **Error Handling**
2451 * Add context to errors at process, MCP, model API, and serialization boundaries
2452 * Report individual query errors without terminating the interactive session
2453 * Validate server commands before running them
2454
24552. **Resource Management**
2456 * Always cancel the MCP session during cleanup
2457 * Ensure cleanup runs even when connection or chat-loop operations fail
2458 * Avoid starting a second server while a session is active
2459
24603. **Security**
2461 * Store API keys securely in `.env`
2462 * Review the tools exposed by a server before allowing model-driven calls
2463 * Connect only to servers and executable commands you trust
2464
2465## Troubleshooting
2466
2467### Server Command Issues
2468
2469The arguments after `cargo run --` must form a complete command. Interpreted server scripts need their runtime:
2470
2471```bash theme={null}
2472# Correct
2473cargo run -- python ./server/weather.py
2474cargo run -- node ./server/build/index.js
2475
2476# Incorrect: a Python script is not necessarily executable by itself
2477cargo run -- ./server/weather.py
2478```
2479
2480If a command cannot be found, use its absolute path or verify it is available in your `PATH`.
2481
2482### Environment File Issues
2483
2484If you see `Failed to load env file`, ensure `.env` exists in the directory where you run the client.
2485
2486If the model request reports a missing API key, confirm that `.env` contains:
2487
2488```text theme={null}
2489ANTHROPIC_API_KEY=your-api-key-goes-here
2490```
2491
2492### Tool and Response Errors
2493
2494* `Unable to list tools from server`: Verify the server starts successfully and communicates over stdio
2495* `Tool call ... failed`: Verify the server tool's required arguments and environment variables
2496* `Failed to serialize tool result`: Inspect the server's response for unsupported or malformed content
25112497
25122498## Next steps
25132499
2514<CardGroup cols={2}>
2515 <Card title="Example servers" icon="grid" href="/examples">
2516 Check out our gallery of official MCP servers and implementations
2517 </Card>
2518</CardGroup>
2500> **[Example servers](/examples)**
2501>
2502> Check out our gallery of official MCP servers and implementations
25192503
docs/2026-07-28/develop/build-server Changed · +2868 / -2936 lines
### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and setting up the instance ### Helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and setting up constants ### Helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Logging in MCP Servers ### Best Practices ### System requirements ### Set up your environment ## Building your server ### Weather Service ### Create your Boot Application ### Running the server ## Testing your server with Claude for Desktop ## Testing your server with Java client ### Create an MCP Client manually ### Use MCP Client Boot Starter ## More Java MCP Server examples ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### System requirements ### Set up your environment ## Building your server ### Setting up the instance ### Weather API helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### System requirements ### Set up your environment ## Building your server ### Weather API helper functions ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and setting up constants ### Helper methods ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and constants ### Data structures ### Helper functions ### Implementing the Weather server and tools ### Implementing the ServerHandler ### Running the server ## Testing your server with Claude for Desktop ### Prerequisite knowledge ### Logging in MCP Servers ### Best Practices ### Quick Examples ### System requirements ### Set up your environment ## Building your server ### Importing packages and constants ### Data structures ### Helper functions ### Implementing tool execution ### Running the server ## Testing your server with Claude for Desktop
The two sides of this change are more than 400 edits apart, too far apart to line up, so this is the differ's own diff of it and the words inside a line are not marked.
from line 8
88
99We'll build a server that exposes two tools: `get_alerts` and `get_forecast`. Then we'll connect the server to an MCP host (in this case, Claude for Desktop):
1010
11<Frame>
12 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/current-weather.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=dce7b2f8a06c20ba358e4bd2e75fa4c7" width="2780" height="1849" data-path="images/current-weather.png" />
13</Frame>
14
15<Note>
16 Servers can connect to any client. We've chosen Claude for Desktop here for simplicity, but we also have a guide on [building your own client](/docs/2026-07-28/develop/build-client).
17</Note>
11
12
13> [!NOTE]
14>
15> Servers can connect to any client. We've chosen Claude for Desktop here for simplicity, but we also have a guide on [building your own client](/docs/2026-07-28/develop/build-client).
1816
1917### Core MCP Concepts
2018
from line 24
2624
2725This tutorial will primarily focus on tools.
2826
29<Tabs>
30 <Tab title="Python">
31 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python)
32
33 ### Prerequisite knowledge
34
35 This quickstart assumes you have familiarity with:
36
37 * Python
38 * LLMs like Claude
39
40 ### Logging in MCP Servers
41
42 When implementing MCP servers, be careful about how you handle logging:
43
44 **For STDIO-based servers:** Never write to stdout. Writing to stdout will corrupt the JSON-RPC messages and break your server. The `print()` function writes to stdout by default, so keep it out of a STDIO server entirely.
45
46 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
47
48 ### Best Practices
49
50 * Use the standard library `logging` module, which writes to stderr.
51 * Create one logger per module with `logging.getLogger(__name__)` and call it from your tools.
52
53 ### Quick Examples
54
55 ```python theme={null}
56 import logging
57
58 logger = logging.getLogger(__name__)
59
60 # ❌ Bad (STDIO)
61 print("Processing request")
62
63 # ✅ Good (STDIO)
64 logger.info("Processing request") # writes to stderr
65 ```
66
67 ### System requirements
68
69 * Python 3.10 or higher installed.
70 * You must use the Python MCP SDK 2.0.0 or higher.
71
72 ### Set up your environment
73
74 First, let's install `uv` and set up our Python project and environment:
75
76 <CodeGroup>
77 ```bash macOS/Linux theme={null}
78 curl -LsSf https://astral.sh/uv/install.sh | sh
79 ```
80
81 ```powershell Windows theme={null}
82 powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"
83 ```
84 </CodeGroup>
85
86 Make sure to restart your terminal afterwards to ensure that the `uv` command gets picked up.
87
88 Now, let's create and set up our project:
89
90 <CodeGroup>
91 ```bash macOS/Linux theme={null}
92 # Create a new directory for our project
93 uv init weather
94 cd weather
95
96 # Create virtual environment and activate it
97 uv venv
98 source .venv/bin/activate
99
100 # Install dependencies
101 uv add "mcp[cli]"
102
103 # Create our server file
104 touch weather.py
105 ```
106
107 ```powershell Windows theme={null}
108 # Create a new directory for our project
109 uv init weather
110 cd weather
111
112 # Create virtual environment and activate it
113 uv venv
114 .venv\Scripts\activate
115
116 # Install dependencies
117 uv add mcp[cli]
118
119 # Create our server file
120 new-item weather.py
121 ```
122 </CodeGroup>
123
124 Now let's dive into building your server.
125
126 ## Building your server
127
128 ### Importing packages and setting up the instance
129
130 Add these to the top of your `weather.py`:
131
132 ```python theme={null}
133 from typing import Any
134
135 import httpx2
136 from mcp.server import MCPServer
137
138 # Initialize MCPServer
139 mcp = MCPServer("weather")
140
141 # Constants
142 NWS_API_BASE = "https://api.weather.gov"
143 USER_AGENT = "weather-app/1.0"
144 ```
145
146 `httpx2` is the HTTP client the SDK itself depends on, so installing `mcp` already brought it in.
147
148 The MCPServer class uses Python type hints and docstrings to automatically generate tool definitions, making it easy to create and maintain MCP tools.
149
150 ### Helper functions
151
152 Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
153
154 ```python theme={null}
155 async def make_nws_request(url: str) -> dict[str, Any] | None:
156 """Make a request to the NWS API with proper error handling."""
157 headers = {"User-Agent": USER_AGENT, "Accept": "application/geo+json"}
158 async with httpx2.AsyncClient() as client:
159 try:
160 response = await client.get(url, headers=headers, timeout=30.0)
161 response.raise_for_status()
162 return response.json()
163 except Exception:
164 return None
165
166
167 def format_alert(feature: dict) -> str:
168 """Format an alert feature into a readable string."""
169 props = feature["properties"]
170 return f"""
171 Event: {props.get("event", "Unknown")}
172 Area: {props.get("areaDesc", "Unknown")}
173 Severity: {props.get("severity", "Unknown")}
174 Description: {props.get("description", "No description available")}
175 Instructions: {props.get("instruction", "No specific instructions provided")}
27**Python**
28
29Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-python)
30
31### Prerequisite knowledge
32
33This quickstart assumes you have familiarity with:
34
35* Python
36* LLMs like Claude
37
38### Logging in MCP Servers
39
40When implementing MCP servers, be careful about how you handle logging:
41
42**For STDIO-based servers:** Never write to stdout. Writing to stdout will corrupt the JSON-RPC messages and break your server. The `print()` function writes to stdout by default, so keep it out of a STDIO server entirely.
43
44**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
45
46### Best Practices
47
48* Use the standard library `logging` module, which writes to stderr.
49* Create one logger per module with `logging.getLogger(__name__)` and call it from your tools.
50
51### Quick Examples
52
53```python theme={null}
54import logging
55
56logger = logging.getLogger(__name__)
57
58# ❌ Bad (STDIO)
59print("Processing request")
60
61# ✅ Good (STDIO)
62logger.info("Processing request") # writes to stderr
63```
64
65### System requirements
66
67* Python 3.10 or higher installed.
68* You must use the Python MCP SDK 2.0.0 or higher.
69
70### Set up your environment
71
72First, let's install `uv` and set up our Python project and environment:
73
74```bash macOS/Linux theme={null}
75curl -LsSf https://astral.sh/uv/install.sh | sh
76```
77
78```powershell Windows theme={null}
79powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex"
80```
81
82Make sure to restart your terminal afterwards to ensure that the `uv` command gets picked up.
83
84Now, let's create and set up our project:
85
86```bash macOS/Linux theme={null}
87# Create a new directory for our project
88uv init weather
89cd weather
90
91# Create virtual environment and activate it
92uv venv
93source .venv/bin/activate
94
95# Install dependencies
96uv add "mcp[cli]"
97
98# Create our server file
99touch weather.py
100```
101
102```powershell Windows theme={null}
103# Create a new directory for our project
104uv init weather
105cd weather
106
107# Create virtual environment and activate it
108uv venv
109.venv\Scripts\activate
110
111# Install dependencies
112uv add mcp[cli]
113
114# Create our server file
115new-item weather.py
116```
117
118Now let's dive into building your server.
119
120## Building your server
121
122### Importing packages and setting up the instance
123
124Add these to the top of your `weather.py`:
125
126```python theme={null}
127from typing import Any
128
129import httpx2
130from mcp.server import MCPServer
131
132# Initialize MCPServer
133mcp = MCPServer("weather")
134
135# Constants
136NWS_API_BASE = "https://api.weather.gov"
137USER_AGENT = "weather-app/1.0"
138```
139
140`httpx2` is the HTTP client the SDK itself depends on, so installing `mcp` already brought it in.
141
142The MCPServer class uses Python type hints and docstrings to automatically generate tool definitions, making it easy to create and maintain MCP tools.
143
144### Helper functions
145
146Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
147
148```python theme={null}
149async def make_nws_request(url: str) -> dict[str, Any] | None:
150 """Make a request to the NWS API with proper error handling."""
151 headers = {"User-Agent": USER_AGENT, "Accept": "application/geo+json"}
152 async with httpx2.AsyncClient() as client:
153 try:
154 response = await client.get(url, headers=headers, timeout=30.0)
155 response.raise_for_status()
156 return response.json()
157 except Exception:
158 return None
159
160
161def format_alert(feature: dict) -> str:
162 """Format an alert feature into a readable string."""
163 props = feature["properties"]
164 return f"""
165Event: {props.get("event", "Unknown")}
166Area: {props.get("areaDesc", "Unknown")}
167Severity: {props.get("severity", "Unknown")}
168Description: {props.get("description", "No description available")}
169Instructions: {props.get("instruction", "No specific instructions provided")}
170"""
171```
172
173### Implementing tool execution
174
175The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
176
177```python theme={null}
178@mcp.tool()
179async def get_alerts(state: str) -> str:
180 """Get weather alerts for a US state.
181
182 Args:
183 state: Two-letter US state code (e.g. CA, NY)
176184 """
177 ```
178
179 ### Implementing tool execution
180
181 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
182
183 ```python theme={null}
184 @mcp.tool()
185 async def get_alerts(state: str) -> str:
186 """Get weather alerts for a US state.
187
188 Args:
189 state: Two-letter US state code (e.g. CA, NY)
185 url = f"{NWS_API_BASE}/alerts/active/area/{state}"
186 data = await make_nws_request(url)
187
188 if not data or "features" not in data:
189 return "Unable to fetch alerts or no alerts found."
190
191 if not data["features"]:
192 return "No active alerts for this state."
193
194 alerts = [format_alert(feature) for feature in data["features"]]
195 return "\n---\n".join(alerts)
196
197
198@mcp.tool()
199async def get_forecast(latitude: float, longitude: float) -> str:
200 """Get weather forecast for a location.
201
202 Args:
203 latitude: Latitude of the location
204 longitude: Longitude of the location
205 """
206 # First get the forecast grid endpoint
207 points_url = f"{NWS_API_BASE}/points/{latitude},{longitude}"
208 points_data = await make_nws_request(points_url)
209
210 if not points_data:
211 return "Unable to fetch forecast data for this location."
212
213 # Get the forecast URL from the points response
214 forecast_url = points_data["properties"]["forecast"]
215 forecast_data = await make_nws_request(forecast_url)
216
217 if not forecast_data:
218 return "Unable to fetch detailed forecast."
219
220 # Format the periods into a readable forecast
221 periods = forecast_data["properties"]["periods"]
222 forecasts = []
223 for period in periods[:5]: # Only show next 5 periods
224 forecast = f"""
225{period["name"]}:
226Temperature: {period["temperature"]}°{period["temperatureUnit"]}
227Wind: {period["windSpeed"]} {period["windDirection"]}
228Forecast: {period["detailedForecast"]}
229"""
230 forecasts.append(forecast)
231
232 return "\n---\n".join(forecasts)
233```
234
235### Running the server
236
237Finally, let's initialize and run the server:
238
239```python theme={null}
240if __name__ == "__main__":
241 mcp.run(transport="stdio")
242```
243
244Your server is complete! Run `uv run weather.py` to start the MCP server, which will listen for messages from MCP hosts.
245
246Let's now test your server from an existing MCP host, Claude for Desktop.
247
248## Testing your server with Claude for Desktop
249
250First, make sure you have Claude for Desktop installed. [You can install the latest version
251here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
252
253We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
254
255For example, if you have [VS Code](https://code.visualstudio.com/) installed:
256
257```bash Linux theme={null}
258code ~/.config/Claude/claude_desktop_config.json
259```
260
261```bash macOS theme={null}
262code ~/Library/Application\ Support/Claude/claude_desktop_config.json
263```
264
265```powershell Windows theme={null}
266code $env:AppData\Claude\claude_desktop_config.json
267```
268
269You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
270
271In this case, we'll add our single weather server like so:
272
273```json macOS/Linux theme={null}
274{
275 "mcpServers": {
276 "weather": {
277 "command": "uv",
278 "args": [
279 "--directory",
280 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather",
281 "run",
282 "weather.py"
283 ]
284 }
285 }
286}
287```
288
289```json Windows theme={null}
290{
291 "mcpServers": {
292 "weather": {
293 "command": "uv",
294 "args": [
295 "--directory",
296 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather",
297 "run",
298 "weather.py"
299 ]
300 }
301 }
302}
303```
304
305> [!WARNING]
306>
307> You may need to put the full path to the `uv` executable in the `command` field. You can get this by running `which uv` on macOS/Linux or `where uv` on Windows.
308
309> [!NOTE]
310>
311> Make sure you pass in the absolute path to your server. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
312
313This tells Claude for Desktop:
314
3151. There's an MCP server named "weather"
3162. To launch it by running `uv --directory /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather run weather.py`
317
318Save the file, and restart **Claude for Desktop**.
319
320**TypeScript**
321
322Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript)
323
324### Prerequisite knowledge
325
326This quickstart assumes you have familiarity with:
327
328* TypeScript
329* LLMs like Claude
330
331### Logging in MCP Servers
332
333When implementing MCP servers, be careful about how you handle logging:
334
335**For STDIO-based servers:** Never use `console.log()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
336
337**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
338
339### Best Practices
340
341* Use `console.error()` which writes to stderr, or use a logging library that writes to stderr or files.
342
343### Quick Examples
344
345```javascript theme={null}
346// ❌ Bad (STDIO)
347console.log("Server started");
348
349// ✅ Good (STDIO)
350console.error("Server started"); // stderr is safe
351```
352
353### System requirements
354
355For TypeScript, make sure you have the latest version of Node installed.
356
357### Set up your environment
358
359First, let's install Node.js and npm if you haven't already. You can download them from [nodejs.org](https://nodejs.org/).
360Verify your Node.js installation:
361
362```bash theme={null}
363node --version
364npm --version
365```
366
367For this tutorial, you'll need Node.js version 20 or higher.
368
369Now, let's create and set up our project:
370
371```bash macOS/Linux theme={null}
372# Create a new directory for our project
373mkdir weather
374cd weather
375
376# Initialize a new npm project
377npm init -y
378
379# Install dependencies
380npm install @modelcontextprotocol/server zod
381npm install -D @types/node typescript
382
383# Create our files
384mkdir src
385touch src/index.ts
386```
387
388```powershell Windows theme={null}
389# Create a new directory for our project
390md weather
391cd weather
392
393# Initialize a new npm project
394npm init -y
395
396# Install dependencies
397npm install @modelcontextprotocol/server zod
398npm install -D @types/node typescript
399
400# Create our files
401md src
402new-item src\index.ts
403```
404
405Update your package.json to add type: "module" and a build script:
406
407```json package.json theme={null}
408{
409 "type": "module",
410 "bin": {
411 "weather": "./build/index.js"
412 },
413 "scripts": {
414 "build": "tsc && chmod 755 build/index.js"
415 },
416 "files": ["build"]
417}
418```
419
420Create a `tsconfig.json` in the root of your project:
421
422```json tsconfig.json theme={null}
423{
424 "compilerOptions": {
425 "target": "ES2022",
426 "module": "Node16",
427 "moduleResolution": "Node16",
428 "types": ["node"],
429 "outDir": "./build",
430 "rootDir": "./src",
431 "strict": true,
432 "esModuleInterop": true,
433 "skipLibCheck": true,
434 "forceConsistentCasingInFileNames": true
435 },
436 "include": ["src/**/*"],
437 "exclude": ["node_modules"]
438}
439```
440
441Now let's dive into building your server.
442
443## Building your server
444
445### Importing packages and setting up constants
446
447Add these to the top of your `src/index.ts`:
448
449```typescript theme={null}
450import { McpServer } from "@modelcontextprotocol/server";
451import { serveStdio } from "@modelcontextprotocol/server/stdio";
452import { z } from "zod";
453
454const NWS_API_BASE = "https://api.weather.gov";
455const USER_AGENT = "weather-app/1.0";
456```
457
458### Helper functions
459
460Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
461
462```typescript theme={null}
463// Helper function for making NWS API requests
464async function makeNWSRequest<T>(url: string): Promise<T | null> {
465 const headers = {
466 "User-Agent": USER_AGENT,
467 Accept: "application/geo+json",
468 };
469
470 try {
471 const response = await fetch(url, { headers });
472 if (!response.ok) {
473 throw new Error(`HTTP error! status: ${response.status}`);
474 }
475 return (await response.json()) as T;
476 } catch (error) {
477 console.error("Error making NWS request:", error);
478 return null;
479 }
480}
481
482interface AlertFeature {
483 properties: {
484 event?: string;
485 areaDesc?: string;
486 severity?: string;
487 status?: string;
488 headline?: string;
489 };
490}
491
492// Format alert data
493function formatAlert(feature: AlertFeature): string {
494 const props = feature.properties;
495 return [
496 `Event: ${props.event || "Unknown"}`,
497 `Area: ${props.areaDesc || "Unknown"}`,
498 `Severity: ${props.severity || "Unknown"}`,
499 `Status: ${props.status || "Unknown"}`,
500 `Headline: ${props.headline || "No headline"}`,
501 "---",
502 ].join("\n");
503}
504
505interface ForecastPeriod {
506 name?: string;
507 temperature?: number;
508 temperatureUnit?: string;
509 windSpeed?: string;
510 windDirection?: string;
511 shortForecast?: string;
512}
513
514interface AlertsResponse {
515 features: AlertFeature[];
516}
517
518interface PointsResponse {
519 properties: {
520 forecast?: string;
521 };
522}
523
524interface ForecastResponse {
525 properties: {
526 periods: ForecastPeriod[];
527 };
528}
529```
530
531### Implementing tool execution
532
533The tool execution handler is responsible for actually executing the logic of each tool. Let's add it, inside a `createServer()` function that builds the server instance and registers both tools on it:
534
535```typescript theme={null}
536// Build a server instance and register its tools. serveStdio calls this
537// whenever it needs an instance, so every call must return a fresh one.
538function createServer() {
539 const server = new McpServer({
540 name: "weather",
541 version: "1.0.0",
542 });
543
544 server.registerTool(
545 "get_alerts",
546 {
547 description: "Get weather alerts for a state",
548 inputSchema: z.object({
549 state: z
550 .string()
551 .length(2)
552 .describe("Two-letter state code (e.g. CA, NY)"),
553 }),
554 },
555 async ({ state }) => {
556 const stateCode = state.toUpperCase();
557 const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`;
558 const alertsData = await makeNWSRequest<AlertsResponse>(alertsUrl);
559
560 if (!alertsData) {
561 return {
562 content: [
563 {
564 type: "text",
565 text: "Failed to retrieve alerts data",
566 },
567 ],
568 };
569 }
570
571 const features = alertsData.features || [];
572 if (!features.length) {
573 return {
574 content: [
575 {
576 type: "text",
577 text: `No active alerts for ${stateCode}`,
578 },
579 ],
580 };
581 }
582
583 const formattedAlerts = features.map(formatAlert);
584 const alertsText = `Active alerts for ${stateCode}:\n\n${formattedAlerts.join("\n")}`;
585
586 return {
587 content: [
588 {
589 type: "text",
590 text: alertsText,
591 },
592 ],
593 };
594 },
595 );
596
597 server.registerTool(
598 "get_forecast",
599 {
600 description: "Get weather forecast for a location",
601 inputSchema: z.object({
602 latitude: z
603 .number()
604 .min(-90)
605 .max(90)
606 .describe("Latitude of the location"),
607 longitude: z
608 .number()
609 .min(-180)
610 .max(180)
611 .describe("Longitude of the location"),
612 }),
613 },
614 async ({ latitude, longitude }) => {
615 // Get grid point data
616 const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`;
617 const pointsData = await makeNWSRequest<PointsResponse>(pointsUrl);
618
619 if (!pointsData) {
620 return {
621 content: [
622 {
623 type: "text",
624 text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`,
625 },
626 ],
627 };
628 }
629
630 const forecastUrl = pointsData.properties?.forecast;
631 if (!forecastUrl) {
632 return {
633 content: [
634 {
635 type: "text",
636 text: "Failed to get forecast URL from grid point data",
637 },
638 ],
639 };
640 }
641
642 // Get forecast data
643 const forecastData = await makeNWSRequest<ForecastResponse>(forecastUrl);
644 if (!forecastData) {
645 return {
646 content: [
647 {
648 type: "text",
649 text: "Failed to retrieve forecast data",
650 },
651 ],
652 };
653 }
654
655 const periods = forecastData.properties?.periods || [];
656 if (periods.length === 0) {
657 return {
658 content: [
659 {
660 type: "text",
661 text: "No forecast periods available",
662 },
663 ],
664 };
665 }
666
667 // Format forecast periods
668 const formattedForecast = periods.map((period: ForecastPeriod) =>
669 [
670 `${period.name || "Unknown"}:`,
671 `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
672 `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
673 `${period.shortForecast || "No forecast available"}`,
674 "---",
675 ].join("\n"),
676 );
677
678 const forecastText = `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join("\n")}`;
679
680 return {
681 content: [
682 {
683 type: "text",
684 text: forecastText,
685 },
686 ],
687 };
688 },
689 );
690
691 return server;
692}
693```
694
695### Running the server
696
697Finally, serve the server over stdio:
698
699```typescript theme={null}
700serveStdio(createServer, {
701 onerror: (error) => console.error("Weather MCP Server error:", error),
702});
703console.error("Weather MCP Server running on stdio");
704```
705
706`serveStdio` negotiates the protocol revision with each client, so the same server answers both 2026-07-28 clients and clients that still open with the 2025-era `initialize` handshake. It calls `createServer()` whenever it needs an instance, including once for a `server/discover` probe that is discarded if the client falls back to `initialize`, which is why the factory returns a new `McpServer` on every call. Wiring the server by hand with `server.connect(new StdioServerTransport())` still compiles, but a server started that way only serves 2025-era clients.
707
708Make sure to run `npm run build` to build your server! This is a very important step in getting your server to connect.
709
710To check that the server answers 2026-07-28 clients, list its tools with the [Inspector CLI](/docs/2026-07-28/tools/inspector/cli) in the `modern` [protocol era](/docs/2026-07-28/tools/inspector/protocol-eras):
711
712```bash theme={null}
713npx @modelcontextprotocol/inspector --cli node build/index.js --protocol-era modern --method tools/list
714```
715
716The Inspector defaults to the `legacy` era, which only exercises the 2025-era handshake, so run the same command once more with `--protocol-era legacy`. Both runs list `get_alerts` and `get_forecast`.
717
718Let's now test your server from an existing MCP host, Claude for Desktop.
719
720## Testing your server with Claude for Desktop
721
722First, make sure you have Claude for Desktop installed. [You can install the latest version
723here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
724
725We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
726
727For example, if you have [VS Code](https://code.visualstudio.com/) installed:
728
729```bash Linux theme={null}
730code ~/.config/Claude/claude_desktop_config.json
731```
732
733```bash macOS theme={null}
734code ~/Library/Application\ Support/Claude/claude_desktop_config.json
735```
736
737```powershell Windows theme={null}
738code $env:AppData\Claude\claude_desktop_config.json
739```
740
741You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
742
743In this case, we'll add our single weather server like so:
744
745```json macOS/Linux theme={null}
746{
747 "mcpServers": {
748 "weather": {
749 "command": "node",
750 "args": ["/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js"]
751 }
752 }
753}
754```
755
756```json Windows theme={null}
757{
758 "mcpServers": {
759 "weather": {
760 "command": "node",
761 "args": ["C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\index.js"]
762 }
763 }
764}
765```
766
767This tells Claude for Desktop:
768
7691. There's an MCP server named "weather"
7702. Launch it by running `node /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js`
771
772Save the file, and restart **Claude for Desktop**.
773
774**Java**
775
776> [!NOTE]
777>
778> This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
779> To learn how to create sync and async MCP Servers, manually, consult the [Java SDK Server](https://java.sdk.modelcontextprotocol.io/) documentation.
780
781Let's get started with building our weather server!
782[You can find the complete code for what we'll be building here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-stdio-server)
783
784For more information, see the [MCP Server Boot Starter](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html) reference documentation.
785For manual MCP Server implementation, refer to the [MCP Server Java SDK documentation](https://java.sdk.modelcontextprotocol.io/).
786
787### Logging in MCP Servers
788
789When implementing MCP servers, be careful about how you handle logging:
790
791**For STDIO-based servers:** Never use `System.out.println()` or `System.out.print()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
792
793**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
794
795### Best Practices
796
797* Use a logging library that writes to stderr or files.
798* Ensure any configured logging library will not write to stdout.
799
800### System requirements
801
802* Java 17 or higher installed.
803* [Spring Boot 3.3.x](https://docs.spring.io/spring-boot/installing.html) or higher
804
805### Set up your environment
806
807Use the [Spring Initializer](https://start.spring.io/) to bootstrap the project.
808
809You will need to add the following dependencies:
810
811```xml Maven theme={null}
812<dependencies>
813 <dependency>
814 <groupId>org.springframework.ai</groupId>
815 <artifactId>spring-ai-starter-mcp-server</artifactId>
816 </dependency>
817
818 <dependency>
819 <groupId>org.springframework</groupId>
820 <artifactId>spring-web</artifactId>
821 </dependency>
822</dependencies>
823```
824
825```groovy Gradle theme={null}
826dependencies {
827 implementation platform("org.springframework.ai:spring-ai-starter-mcp-server")
828 implementation platform("org.springframework:spring-web")
829}
830```
831
832Then configure your application by setting the application properties:
833
834```bash application.properties theme={null}
835spring.main.bannerMode=off
836logging.pattern.console=
837```
838
839```yaml application.yml theme={null}
840logging:
841 pattern:
842 console:
843spring:
844 main:
845 banner-mode: off
846```
847
848The [Server Configuration Properties](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html#_configuration_properties) documents all available properties.
849
850Now let's dive into building your server.
851
852## Building your server
853
854### Weather Service
855
856Let's implement a [WeatherService.java](https://github.com/spring-projects/spring-ai-examples/blob/main/model-context-protocol/weather/starter-stdio-server/src/main/java/org/springframework/ai/mcp/sample/server/WeatherService.java) that uses a REST client to query the data from the National Weather Service API:
857
858```java theme={null}
859@Service
860public class WeatherService {
861
862 private final RestClient restClient;
863
864 public WeatherService() {
865 this.restClient = RestClient.builder()
866 .baseUrl("https://api.weather.gov")
867 .defaultHeader("Accept", "application/geo+json")
868 .defaultHeader("User-Agent", "WeatherApiClient/1.0 ([email protected])")
869 .build();
870 }
871
872 @Tool(description = "Get weather forecast for a specific latitude/longitude")
873 public String getWeatherForecastByLocation(
874 double latitude, // Latitude coordinate
875 double longitude // Longitude coordinate
876 ) {
877 // Returns detailed forecast including:
878 // - Temperature and unit
879 // - Wind speed and direction
880 // - Detailed forecast description
881 }
882
883 @Tool(description = "Get weather alerts for a US state")
884 public String getAlerts(
885 @ToolParam(description = "Two-letter US state code (e.g. CA, NY)") String state
886 ) {
887 // Returns active alerts including:
888 // - Event type
889 // - Affected area
890 // - Severity
891 // - Description
892 // - Safety instructions
893 }
894
895 // ......
896}
897```
898
899The `@Service` annotation will auto-register the service in your application context.
900The Spring AI `@Tool` annotation makes it easy to create and maintain MCP tools.
901
902The auto-configuration will automatically register these tools with the MCP server.
903
904### Create your Boot Application
905
906```java theme={null}
907@SpringBootApplication
908public class McpServerApplication {
909
910 public static void main(String[] args) {
911 SpringApplication.run(McpServerApplication.class, args);
912 }
913
914 @Bean
915 public ToolCallbackProvider weatherTools(WeatherService weatherService) {
916 return MethodToolCallbackProvider.builder().toolObjects(weatherService).build();
917 }
918}
919```
920
921Uses the `MethodToolCallbackProvider` utils to convert the `@Tools` into actionable callbacks used by the MCP server.
922
923### Running the server
924
925Finally, let's build the server:
926
927```bash theme={null}
928./mvnw clean install
929```
930
931This will generate an `mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar` file within the `target` folder.
932
933Let's now test your server from an existing MCP host, Claude for Desktop.
934
935## Testing your server with Claude for Desktop
936
937First, make sure you have Claude for Desktop installed.
938[You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
939
940We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
941To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
942Make sure to create the file if it doesn't exist.
943
944For example, if you have [VS Code](https://code.visualstudio.com/) installed:
945
946```bash Linux theme={null}
947code ~/.config/Claude/claude_desktop_config.json
948```
949
950```bash macOS theme={null}
951code ~/Library/Application\ Support/Claude/claude_desktop_config.json
952```
953
954```powershell Windows theme={null}
955code $env:AppData\Claude\claude_desktop_config.json
956```
957
958You'll then add your servers in the `mcpServers` key.
959The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
960
961In this case, we'll add our single weather server like so:
962
963```json macOS/Linux theme={null}
964{
965 "mcpServers": {
966 "spring-ai-mcp-weather": {
967 "command": "java",
968 "args": [
969 "-Dspring.ai.mcp.server.stdio=true",
970 "-jar",
971 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
972 ]
973 }
974 }
975}
976```
977
978```json Windows theme={null}
979{
980 "mcpServers": {
981 "spring-ai-mcp-weather": {
982 "command": "java",
983 "args": [
984 "-Dspring.ai.mcp.server.transport=STDIO",
985 "-jar",
986 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
987 ]
988 }
989 }
990}
991```
992
993> [!NOTE]
994>
995> Make sure you pass in the absolute path to your server.
996
997This tells Claude for Desktop:
998
9991. There's an MCP server named "my-weather-server"
10002. To launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar`
1001
1002Save the file, and restart **Claude for Desktop**.
1003
1004## Testing your server with Java client
1005
1006### Create an MCP Client manually
1007
1008Use the `McpClient` to connect to the server:
1009
1010```java theme={null}
1011var stdioParams = ServerParameters.builder("java")
1012 .args("-jar", "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar")
1013 .build();
1014
1015var stdioTransport = new StdioClientTransport(stdioParams);
1016
1017var mcpClient = McpClient.sync(stdioTransport).build();
1018
1019mcpClient.initialize();
1020
1021ListToolsResult toolsList = mcpClient.listTools();
1022
1023CallToolResult weather = mcpClient.callTool(
1024 new CallToolRequest("getWeatherForecastByLocation",
1025 Map.of("latitude", "47.6062", "longitude", "-122.3321")));
1026
1027CallToolResult alert = mcpClient.callTool(
1028 new CallToolRequest("getAlerts", Map.of("state", "NY")));
1029
1030mcpClient.closeGracefully();
1031```
1032
1033### Use MCP Client Boot Starter
1034
1035Create a new boot starter application using the `spring-ai-starter-mcp-client` dependency:
1036
1037```xml theme={null}
1038<dependency>
1039 <groupId>org.springframework.ai</groupId>
1040 <artifactId>spring-ai-starter-mcp-client</artifactId>
1041</dependency>
1042```
1043
1044and set the `spring.ai.mcp.client.stdio.servers-configuration` property to point to your `claude_desktop_config.json`.
1045You can reuse the existing Anthropic Desktop configuration:
1046
1047```properties theme={null}
1048spring.ai.mcp.client.stdio.servers-configuration=file:PATH/TO/claude_desktop_config.json
1049```
1050
1051When you start your client application, the auto-configuration will automatically create MCP clients from the claude\_desktop\_config.json.
1052
1053For more information, see the [MCP Client Boot Starters](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-client-boot-starter-docs.html) reference documentation.
1054
1055## More Java MCP Server examples
1056
1057The [starter-webflux-server](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-webflux-server) demonstrates how to create an HTTP-based MCP server with the WebFlux starter.
1058Set the `spring.ai.mcp.server.protocol=STREAMABLE` property to serve it over Streamable HTTP.
1059It showcases how to define and register MCP Tools, Resources, and Prompts, using the Spring Boot's auto-configuration capabilities.
1060
1061**Kotlin**
1062
1063Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/weather-stdio-server)
1064
1065### Prerequisite knowledge
1066
1067This quickstart assumes you have familiarity with:
1068
1069* Kotlin
1070* LLMs like Claude
1071
1072### Logging in MCP Servers
1073
1074When implementing MCP servers, be careful about how you handle logging:
1075
1076**For STDIO-based servers:** Never use `println()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1077
1078**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1079
1080### Best Practices
1081
1082* Use a logging library that writes to stderr or files.
1083
1084### System requirements
1085
1086* JDK 11 or higher installed.
1087
1088### Set up your environment
1089
1090First, let's install `java` and `gradle` if you haven't already.
1091You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1092Verify your `java` installation:
1093
1094```bash theme={null}
1095java --version
1096```
1097
1098Now, let's create and set up your project:
1099
1100```bash macOS/Linux theme={null}
1101# Create a new directory for our project
1102mkdir weather
1103cd weather
1104
1105# Initialize a new kotlin project
1106gradle init
1107```
1108
1109```powershell Windows theme={null}
1110# Create a new directory for our project
1111md weather
1112cd weather
1113
1114# Initialize a new kotlin project
1115gradle init
1116```
1117
1118After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1119
1120Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1121
1122After creating the project, replace the contents of your `build.gradle.kts` with:
1123
1124```kotlin build.gradle.kts theme={null}
1125// Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1126val mcpVersion = "0.9.0"
1127val ktorVersion = "3.2.3"
1128val slf4jVersion = "2.0.17"
1129
1130plugins {
1131 kotlin("jvm") version "2.3.20"
1132 kotlin("plugin.serialization") version "2.3.20"
1133 id("com.gradleup.shadow") version "8.3.9"
1134 application
1135}
1136
1137application {
1138 mainClass.set("MainKt")
1139}
1140
1141dependencies {
1142 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1143 implementation("io.ktor:ktor-client-content-negotiation:$ktorVersion")
1144 implementation("io.ktor:ktor-serialization-kotlinx-json:$ktorVersion")
1145 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1146 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1147}
1148```
1149
1150Verify that everything is set up correctly:
1151
1152```bash theme={null}
1153./gradlew build
1154```
1155
1156Now let's dive into building your server.
1157
1158## Building your server
1159
1160### Setting up the instance
1161
1162Add a server initialization function:
1163
1164```kotlin theme={null}
1165fun runMcpServer() {
1166 val server = Server(
1167 Implementation(
1168 name = "weather",
1169 version = "1.0.0",
1170 ),
1171 ServerOptions(
1172 capabilities = ServerCapabilities(tools = ServerCapabilities.Tools(listChanged = true)),
1173 ),
1174 )
1175
1176 // register tools on server here
1177
1178 val transport = StdioServerTransport(
1179 System.`in`.asInput(),
1180 System.out.asSink().buffered(),
1181 )
1182
1183 runBlocking {
1184 val session = server.createSession(transport)
1185 val done = Job()
1186 session.onClose {
1187 done.complete()
1188 }
1189 done.join()
1190 }
1191}
1192```
1193
1194### Weather API helper functions
1195
1196Next, let's add functions and data classes for querying and converting responses from the National Weather Service API:
1197
1198```kotlin theme={null}
1199val httpClient = HttpClient(CIO) {
1200 defaultRequest {
1201 url("https://api.weather.gov")
1202 headers {
1203 append("Accept", "application/geo+json")
1204 append("User-Agent", "WeatherApiClient/1.0")
1205 }
1206 contentType(ContentType.Application.Json)
1207 }
1208 install(ContentNegotiation) {
1209 json(Json { ignoreUnknownKeys = true })
1210 }
1211}
1212
1213// Extension function to fetch weather alerts for a given state
1214suspend fun HttpClient.getAlerts(state: String): List<String> {
1215 val alerts = this.get("/alerts/active/area/$state").body<AlertsResponse>()
1216 return alerts.features.map { feature ->
1901217 """
191 url = f"{NWS_API_BASE}/alerts/active/area/{state}"
192 data = await make_nws_request(url)
193
194 if not data or "features" not in data:
195 return "Unable to fetch alerts or no alerts found."
196
197 if not data["features"]:
198 return "No active alerts for this state."
199
200 alerts = [format_alert(feature) for feature in data["features"]]
201 return "\n---\n".join(alerts)
202
203
204 @mcp.tool()
205 async def get_forecast(latitude: float, longitude: float) -> str:
206 """Get weather forecast for a location.
207
208 Args:
209 latitude: Latitude of the location
210 longitude: Longitude of the location
1218 Event: ${feature.properties.event}
1219 Area: ${feature.properties.areaDesc}
1220 Severity: ${feature.properties.severity}
1221 Status: ${feature.properties.status}
1222 Headline: ${feature.properties.headline}
1223 """.trimIndent()
1224 }
1225}
1226
1227// Extension function to fetch forecast information for given latitude and longitude
1228suspend fun HttpClient.getForecast(latitude: Double, longitude: Double): List<String> {
1229 val points = this.get("/points/$latitude,$longitude").body<PointsResponse>()
1230 val forecastUrl = points.properties.forecast ?: error("No forecast URL available")
1231 val forecast = this.get(forecastUrl).body<ForecastResponse>()
1232 return forecast.properties.periods.map { period ->
2111233 """
212 # First get the forecast grid endpoint
213 points_url = f"{NWS_API_BASE}/points/{latitude},{longitude}"
214 points_data = await make_nws_request(points_url)
215
216 if not points_data:
217 return "Unable to fetch forecast data for this location."
218
219 # Get the forecast URL from the points response
220 forecast_url = points_data["properties"]["forecast"]
221 forecast_data = await make_nws_request(forecast_url)
222
223 if not forecast_data:
224 return "Unable to fetch detailed forecast."
225
226 # Format the periods into a readable forecast
227 periods = forecast_data["properties"]["periods"]
228 forecasts = []
229 for period in periods[:5]: # Only show next 5 periods
230 forecast = f"""
231 {period["name"]}:
232 Temperature: {period["temperature"]}°{period["temperatureUnit"]}
233 Wind: {period["windSpeed"]} {period["windDirection"]}
234 Forecast: {period["detailedForecast"]}
235 """
236 forecasts.append(forecast)
237
238 return "\n---\n".join(forecasts)
239 ```
240
241 ### Running the server
242
243 Finally, let's initialize and run the server:
244
245 ```python theme={null}
246 if __name__ == "__main__":
247 mcp.run(transport="stdio")
248 ```
249
250 Your server is complete! Run `uv run weather.py` to start the MCP server, which will listen for messages from MCP hosts.
251
252 Let's now test your server from an existing MCP host, Claude for Desktop.
253
254 ## Testing your server with Claude for Desktop
255
256 First, make sure you have Claude for Desktop installed. [You can install the latest version
257 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
258
259 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
260
261 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
262
263 <CodeGroup>
264 ```bash Linux theme={null}
265 code ~/.config/Claude/claude_desktop_config.json
266 ```
267
268 ```bash macOS theme={null}
269 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
270 ```
271
272 ```powershell Windows theme={null}
273 code $env:AppData\Claude\claude_desktop_config.json
274 ```
275 </CodeGroup>
276
277 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
278
279 In this case, we'll add our single weather server like so:
280
281 <CodeGroup>
282 ```json macOS/Linux theme={null}
283 {
284 "mcpServers": {
285 "weather": {
286 "command": "uv",
287 "args": [
288 "--directory",
289 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather",
290 "run",
291 "weather.py"
292 ]
293 }
1234 ${period.name}:
1235 Temperature: ${period.temperature}°${period.temperatureUnit}
1236 Wind: ${period.windSpeed} ${period.windDirection}
1237 ${period.shortForecast}
1238 """.trimIndent()
1239 }
1240}
1241
1242@Serializable
1243data class PointsResponse(val properties: PointsProperties)
1244
1245@Serializable
1246data class PointsProperties(val forecast: String? = null)
1247
1248@Serializable
1249data class ForecastResponse(val properties: ForecastProperties)
1250
1251@Serializable
1252data class ForecastProperties(val periods: List<ForecastPeriod> = emptyList())
1253
1254@Serializable
1255data class ForecastPeriod(
1256 val name: String? = null,
1257 val temperature: Int? = null,
1258 val temperatureUnit: String? = null,
1259 val windSpeed: String? = null,
1260 val windDirection: String? = null,
1261 val shortForecast: String? = null,
1262)
1263
1264@Serializable
1265data class AlertsResponse(val features: List<AlertFeature> = emptyList())
1266
1267@Serializable
1268data class AlertFeature(val properties: AlertProperties)
1269
1270@Serializable
1271data class AlertProperties(
1272 val event: String? = null,
1273 val areaDesc: String? = null,
1274 val severity: String? = null,
1275 val status: String? = null,
1276 val headline: String? = null,
1277)
1278```
1279
1280### Implementing tool execution
1281
1282The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
1283
1284```kotlin theme={null}
1285// Register weather tools
1286
1287server.addTool(
1288 name = "get_alerts",
1289 description = "Get weather alerts for a US state. Input is a two-letter US state code (e.g. CA, NY)",
1290 inputSchema = ToolSchema(
1291 properties = buildJsonObject {
1292 putJsonObject("state") {
1293 put("type", "string")
1294 put("description", "Two-letter US state code (e.g. CA, NY)")
1295 }
1296 },
1297 required = listOf("state"),
1298 ),
1299) { request ->
1300 val state = request.arguments?.get("state")?.jsonPrimitive?.content
1301 ?: return@addTool CallToolResult(
1302 content = listOf(TextContent("The 'state' parameter is required.")),
1303 )
1304
1305 val alerts = httpClient.getAlerts(state)
1306 CallToolResult(content = alerts.map { TextContent(it) })
1307}
1308
1309server.addTool(
1310 name = "get_forecast",
1311 description = "Get weather forecast for a location. Note: only US locations are supported by the NWS API.",
1312 inputSchema = ToolSchema(
1313 properties = buildJsonObject {
1314 putJsonObject("latitude") {
1315 put("type", "number")
1316 put("description", "Latitude of the location")
1317 }
1318 putJsonObject("longitude") {
1319 put("type", "number")
1320 put("description", "Longitude of the location")
1321 }
1322 },
1323 required = listOf("latitude", "longitude"),
1324 ),
1325) { request ->
1326 val latitude = request.arguments?.get("latitude")?.jsonPrimitive?.doubleOrNull
1327 val longitude = request.arguments?.get("longitude")?.jsonPrimitive?.doubleOrNull
1328 if (latitude == null || longitude == null) {
1329 return@addTool CallToolResult(
1330 content = listOf(TextContent("The 'latitude' and 'longitude' parameters are required.")),
1331 )
1332 }
1333
1334 val forecast = httpClient.getForecast(latitude, longitude)
1335 CallToolResult(content = forecast.map { TextContent(it) })
1336}
1337```
1338
1339### Running the server
1340
1341Finally, implement the main function to run the server:
1342
1343```kotlin theme={null}
1344fun main() = runMcpServer()
1345```
1346
1347You can run the server directly during development:
1348
1349```bash theme={null}
1350./gradlew run
1351```
1352
1353For production use, build the shadow JAR:
1354
1355```bash theme={null}
1356./gradlew build
1357java -jar build/libs/weather-0.1.0-all.jar
1358```
1359
1360Let's now test your server from an existing MCP host, Claude for Desktop.
1361
1362## Testing your server with Claude for Desktop
1363
1364First, make sure you have Claude for Desktop installed. [You can install the latest version
1365here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1366
1367We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
1368To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
1369Make sure to create the file if it doesn't exist.
1370
1371For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1372
1373```bash Linux theme={null}
1374code ~/.config/Claude/claude_desktop_config.json
1375```
1376
1377```bash macOS theme={null}
1378code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1379```
1380
1381```powershell Windows theme={null}
1382code $env:AppData\Claude\claude_desktop_config.json
1383```
1384
1385You'll then add your servers in the `mcpServers` key.
1386The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1387
1388In this case, we'll add our single weather server like so:
1389
1390```json macOS/Linux theme={null}
1391{
1392 "mcpServers": {
1393 "weather": {
1394 "command": "java",
1395 "args": [
1396 "-jar",
1397 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar"
1398 ]
1399 }
1400 }
1401}
1402```
1403
1404```json Windows theme={null}
1405{
1406 "mcpServers": {
1407 "weather": {
1408 "command": "java",
1409 "args": [
1410 "-jar",
1411 "C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\libs\\weather-0.1.0-all.jar"
1412 ]
1413 }
1414 }
1415}
1416```
1417
1418This tells Claude for Desktop:
1419
14201. There's an MCP server named "weather"
14212. Launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar`
1422
1423Save the file, and restart **Claude for Desktop**.
1424
1425**C#**
1426
1427Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartWeatherServer)
1428
1429### Prerequisite knowledge
1430
1431This quickstart assumes you have familiarity with:
1432
1433* C#
1434* LLMs like Claude
1435* .NET 8 or higher
1436
1437### Logging in MCP Servers
1438
1439When implementing MCP servers, be careful about how you handle logging:
1440
1441**For STDIO-based servers:** Never use `Console.WriteLine()` or `Console.Write()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
1442
1443**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1444
1445### Best Practices
1446
1447* Use a logging library that writes to stderr or files.
1448
1449### System requirements
1450
1451* [.NET 8 SDK](https://dotnet.microsoft.com/download/dotnet/8.0) or higher installed.
1452
1453### Set up your environment
1454
1455First, let's install `dotnet` if you haven't already. You can download `dotnet` from [official Microsoft .NET website](https://dotnet.microsoft.com/download/). Verify your `dotnet` installation:
1456
1457```bash theme={null}
1458dotnet --version
1459```
1460
1461Now, let's create and set up your project:
1462
1463```bash macOS/Linux theme={null}
1464# Create a new directory for our project
1465mkdir weather
1466cd weather
1467# Initialize a new C# project
1468dotnet new console
1469```
1470
1471```powershell Windows theme={null}
1472# Create a new directory for our project
1473mkdir weather
1474cd weather
1475# Initialize a new C# project
1476dotnet new console
1477```
1478
1479After running `dotnet new console`, you will be presented with a new C# project.
1480You can open the project in your favorite IDE, such as [Visual Studio](https://visualstudio.microsoft.com/) or [Rider](https://www.jetbrains.com/rider/).
1481Alternatively, you can create a C# application using the [Visual Studio project wizard](https://learn.microsoft.com/en-us/visualstudio/get-started/csharp/tutorial-console?view=vs-2022).
1482After creating the project, add NuGet package for the Model Context Protocol SDK and hosting:
1483
1484```bash theme={null}
1485# Add the Model Context Protocol SDK NuGet package
1486dotnet add package ModelContextProtocol --prerelease
1487# Add the .NET Hosting NuGet package
1488dotnet add package Microsoft.Extensions.Hosting
1489```
1490
1491Now let’s dive into building your server.
1492
1493## Building your server
1494
1495Open the `Program.cs` file in your project and replace its contents with the following code:
1496
1497```csharp theme={null}
1498using Microsoft.Extensions.DependencyInjection;
1499using Microsoft.Extensions.Hosting;
1500using ModelContextProtocol;
1501using System.Net.Http.Headers;
1502
1503var builder = Host.CreateEmptyApplicationBuilder(settings: null);
1504
1505builder.Services.AddMcpServer()
1506 .WithStdioServerTransport()
1507 .WithToolsFromAssembly();
1508
1509builder.Services.AddSingleton(_ =>
1510{
1511 var client = new HttpClient() { BaseAddress = new Uri("https://api.weather.gov") };
1512 client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("weather-tool", "1.0"));
1513 return client;
1514});
1515
1516var app = builder.Build();
1517
1518await app.RunAsync();
1519```
1520
1521> [!NOTE]
1522>
1523> When creating the `ApplicationHostBuilder`, ensure you use `CreateEmptyApplicationBuilder` instead of `CreateDefaultBuilder`. This ensures that the server does not write any additional messages to the console. This is only necessary for servers using STDIO transport.
1524
1525This code sets up a basic console application that uses the Model Context Protocol SDK to create an MCP server with standard I/O transport.
1526
1527### Weather API helper functions
1528
1529Create an extension class for `HttpClient` which helps simplify JSON request handling:
1530
1531```csharp theme={null}
1532using System.Text.Json;
1533
1534internal static class HttpClientExt
1535{
1536 public static async Task<JsonDocument> ReadJsonDocumentAsync(this HttpClient client, string requestUri)
1537 {
1538 using var response = await client.GetAsync(requestUri);
1539 response.EnsureSuccessStatusCode();
1540 return await JsonDocument.ParseAsync(await response.Content.ReadAsStreamAsync());
1541 }
1542}
1543```
1544
1545Next, define a class with the tool execution handlers for querying and converting responses from the National Weather Service API:
1546
1547```csharp theme={null}
1548using ModelContextProtocol.Server;
1549using System.ComponentModel;
1550using System.Globalization;
1551using System.Text.Json;
1552
1553namespace QuickstartWeatherServer.Tools;
1554
1555[McpServerToolType]
1556public static class WeatherTools
1557{
1558 [McpServerTool, Description("Get weather alerts for a US state code.")]
1559 public static async Task<string> GetAlerts(
1560 HttpClient client,
1561 [Description("The US state code to get alerts for.")] string state)
1562 {
1563 using var jsonDocument = await client.ReadJsonDocumentAsync($"/alerts/active/area/{state}");
1564 var jsonElement = jsonDocument.RootElement;
1565 var alerts = jsonElement.GetProperty("features").EnumerateArray();
1566
1567 if (!alerts.Any())
1568 {
1569 return "No active alerts for this state.";
2941570 }
1571
1572 return string.Join("\n--\n", alerts.Select(alert =>
1573 {
1574 JsonElement properties = alert.GetProperty("properties");
1575 return $"""
1576 Event: {properties.GetProperty("event").GetString()}
1577 Area: {properties.GetProperty("areaDesc").GetString()}
1578 Severity: {properties.GetProperty("severity").GetString()}
1579 Description: {properties.GetProperty("description").GetString()}
1580 Instruction: {properties.GetProperty("instruction").GetString()}
1581 """;
1582 }));
1583 }
1584
1585 [McpServerTool, Description("Get weather forecast for a location.")]
1586 public static async Task<string> GetForecast(
1587 HttpClient client,
1588 [Description("Latitude of the location.")] double latitude,
1589 [Description("Longitude of the location.")] double longitude)
1590 {
1591 var pointUrl = string.Create(CultureInfo.InvariantCulture, $"/points/{latitude},{longitude}");
1592 using var jsonDocument = await client.ReadJsonDocumentAsync(pointUrl);
1593 var forecastUrl = jsonDocument.RootElement.GetProperty("properties").GetProperty("forecast").GetString()
1594 ?? throw new Exception($"No forecast URL provided by {client.BaseAddress}points/{latitude},{longitude}");
1595
1596 using var forecastDocument = await client.ReadJsonDocumentAsync(forecastUrl);
1597 var periods = forecastDocument.RootElement.GetProperty("properties").GetProperty("periods").EnumerateArray();
1598
1599 return string.Join("\n---\n", periods.Select(period => $"""
1600 {period.GetProperty("name").GetString()}
1601 Temperature: {period.GetProperty("temperature").GetInt32()}°F
1602 Wind: {period.GetProperty("windSpeed").GetString()} {period.GetProperty("windDirection").GetString()}
1603 Forecast: {period.GetProperty("detailedForecast").GetString()}
1604 """));
1605 }
1606}
1607```
1608
1609### Running the server
1610
1611Finally, run the server using the following command:
1612
1613```bash theme={null}
1614dotnet run
1615```
1616
1617This will start the server and listen for incoming requests on standard input/output.
1618
1619## Testing your server with Claude for Desktop
1620
1621First, make sure you have Claude for Desktop installed. [You can install the latest version
1622here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1623We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1624For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1625
1626```bash Linux theme={null}
1627code ~/.config/Claude/claude_desktop_config.json
1628```
1629
1630```bash macOS theme={null}
1631code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1632```
1633
1634```powershell Windows theme={null}
1635code $env:AppData\Claude\claude_desktop_config.json
1636```
1637
1638You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1639In this case, we'll add our single weather server like so:
1640
1641```json macOS/Linux theme={null}
1642{
1643 "mcpServers": {
1644 "weather": {
1645 "command": "dotnet",
1646 "args": ["run", "--project", "/ABSOLUTE/PATH/TO/PROJECT", "--no-build"]
1647 }
1648 }
1649}
1650```
1651
1652```json Windows theme={null}
1653{
1654 "mcpServers": {
1655 "weather": {
1656 "command": "dotnet",
1657 "args": [
1658 "run",
1659 "--project",
1660 "C:\\ABSOLUTE\\PATH\\TO\\PROJECT",
1661 "--no-build"
1662 ]
1663 }
1664 }
1665}
1666```
1667
1668This tells Claude for Desktop:
1669
16701. There's an MCP server named "weather"
16712. Launch it by running `dotnet run /ABSOLUTE/PATH/TO/PROJECT`
1672 Save the file, and restart **Claude for Desktop**.
1673
1674**Ruby**
1675
1676Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby)
1677
1678### Prerequisite knowledge
1679
1680This quickstart assumes you have familiarity with:
1681
1682* Ruby
1683* LLMs like Claude
1684
1685### Logging in MCP Servers
1686
1687When implementing MCP servers, be careful about how you handle logging:
1688
1689**For STDIO-based servers:** Never use `puts` or `print`, as they write to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1690
1691**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1692
1693### Best Practices
1694
1695* Use a logging library that writes to stderr or files.
1696
1697### Quick Examples
1698
1699```ruby theme={null}
1700# ❌ Bad (STDIO)
1701puts "Processing request"
1702
1703# ✅ Good (STDIO)
1704require "logger"
1705logger = Logger.new($stderr)
1706logger.info("Processing request")
1707```
1708
1709### System requirements
1710
1711* Ruby 2.7 or higher installed.
1712
1713### Set up your environment
1714
1715First, let's make sure you have Ruby installed. You can check by running:
1716
1717```bash theme={null}
1718ruby --version
1719```
1720
1721Now, let's create and set up our project:
1722
1723```bash macOS/Linux theme={null}
1724# Create a new directory for our project
1725mkdir weather
1726cd weather
1727
1728# Create a Gemfile
1729bundle init
1730
1731# Add the MCP SDK dependency
1732bundle add mcp
1733
1734# Create our server file
1735touch weather.rb
1736```
1737
1738```powershell Windows theme={null}
1739# Create a new directory for our project
1740mkdir weather
1741cd weather
1742
1743# Create a Gemfile
1744bundle init
1745
1746# Add the MCP SDK dependency
1747bundle add mcp
1748
1749# Create our server file
1750new-item weather.rb
1751```
1752
1753Now let's dive into building your server.
1754
1755## Building your server
1756
1757### Importing packages and setting up constants
1758
1759Open `weather.rb` and add these requires and constants at the top:
1760
1761```ruby theme={null}
1762require "json"
1763require "mcp"
1764require "net/http"
1765require "uri"
1766
1767NWS_API_BASE = "https://api.weather.gov"
1768USER_AGENT = "weather-app/1.0"
1769```
1770
1771The `mcp` gem provides the Model Context Protocol SDK for Ruby, with classes for server implementation and stdio transport.
1772
1773### Helper methods
1774
1775Next, let's add helper methods for querying and formatting data from the National Weather Service API:
1776
1777```ruby theme={null}
1778module HelperMethods
1779 def make_nws_request(url)
1780 uri = URI(url)
1781 request = Net::HTTP::Get.new(uri)
1782 request["User-Agent"] = USER_AGENT
1783 request["Accept"] = "application/geo+json"
1784
1785 response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
1786 http.request(request)
1787 end
1788
1789 raise "HTTP #{response.code}: #{response.message}" unless response.is_a?(Net::HTTPSuccess)
1790
1791 JSON.parse(response.body)
1792 end
1793
1794 def format_alert(feature)
1795 properties = feature["properties"]
1796
1797 <<~ALERT
1798 Event: #{properties["event"] || "Unknown"}
1799 Area: #{properties["areaDesc"] || "Unknown"}
1800 Severity: #{properties["severity"] || "Unknown"}
1801 Description: #{properties["description"] || "No description available"}
1802 Instructions: #{properties["instruction"] || "No specific instructions provided"}
1803 ALERT
1804 end
1805end
1806```
1807
1808### Implementing tool execution
1809
1810Now let's define our tool classes. Each tool subclasses `MCP::Tool` and implements the tool logic:
1811
1812```ruby theme={null}
1813class GetAlerts < MCP::Tool
1814 extend HelperMethods
1815
1816 tool_name "get_alerts"
1817 description "Get weather alerts for a US state"
1818 input_schema(
1819 properties: {
1820 state: {
1821 type: "string",
1822 description: "Two-letter US state code (e.g. CA, NY)"
2951823 }
296 ```
297
298 ```json Windows theme={null}
299 {
300 "mcpServers": {
301 "weather": {
302 "command": "uv",
303 "args": [
304 "--directory",
305 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather",
306 "run",
307 "weather.py"
308 ]
309 }
310 }
1824 },
1825 required: ["state"]
1826 )
1827
1828 def self.call(state:)
1829 url = "#{NWS_API_BASE}/alerts/active/area/#{state.upcase}"
1830 data = make_nws_request(url)
1831
1832 if data["features"].empty?
1833 return MCP::Tool::Response.new([{
1834 type: "text",
1835 text: "No active alerts for this state."
1836 }])
1837 end
1838
1839 alerts = data["features"].map { |feature| format_alert(feature) }
1840 MCP::Tool::Response.new([{
1841 type: "text",
1842 text: alerts.join("\n---\n")
1843 }])
1844 end
1845end
1846
1847class GetForecast < MCP::Tool
1848 extend HelperMethods
1849
1850 tool_name "get_forecast"
1851 description "Get weather forecast for a location"
1852 input_schema(
1853 properties: {
1854 latitude: {
1855 type: "number",
1856 description: "Latitude of the location"
1857 },
1858 longitude: {
1859 type: "number",
1860 description: "Longitude of the location"
3111861 }
312 ```
313 </CodeGroup>
314
315 <Warning>
316 You may need to put the full path to the `uv` executable in the `command` field. You can get this by running `which uv` on macOS/Linux or `where uv` on Windows.
317 </Warning>
318
319 <Note>
320 Make sure you pass in the absolute path to your server. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
321 </Note>
322
323 This tells Claude for Desktop:
324
325 1. There's an MCP server named "weather"
326 2. To launch it by running `uv --directory /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather run weather.py`
327
328 Save the file, and restart **Claude for Desktop**.
329 </Tab>
330
331 <Tab title="TypeScript">
332 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-typescript)
333
334 ### Prerequisite knowledge
335
336 This quickstart assumes you have familiarity with:
337
338 * TypeScript
339 * LLMs like Claude
340
341 ### Logging in MCP Servers
342
343 When implementing MCP servers, be careful about how you handle logging:
344
345 **For STDIO-based servers:** Never use `console.log()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
346
347 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
348
349 ### Best Practices
350
351 * Use `console.error()` which writes to stderr, or use a logging library that writes to stderr or files.
352
353 ### Quick Examples
354
355 ```javascript theme={null}
356 // ❌ Bad (STDIO)
357 console.log("Server started");
358
359 // ✅ Good (STDIO)
360 console.error("Server started"); // stderr is safe
361 ```
362
363 ### System requirements
364
365 For TypeScript, make sure you have the latest version of Node installed.
366
367 ### Set up your environment
368
369 First, let's install Node.js and npm if you haven't already. You can download them from [nodejs.org](https://nodejs.org/).
370 Verify your Node.js installation:
371
372 ```bash theme={null}
373 node --version
374 npm --version
375 ```
376
377 For this tutorial, you'll need Node.js version 20 or higher.
378
379 Now, let's create and set up our project:
380
381 <CodeGroup>
382 ```bash macOS/Linux theme={null}
383 # Create a new directory for our project
384 mkdir weather
385 cd weather
386
387 # Initialize a new npm project
388 npm init -y
389
390 # Install dependencies
391 npm install @modelcontextprotocol/server zod
392 npm install -D @types/node typescript
393
394 # Create our files
395 mkdir src
396 touch src/index.ts
397 ```
398
399 ```powershell Windows theme={null}
400 # Create a new directory for our project
401 md weather
402 cd weather
403
404 # Initialize a new npm project
405 npm init -y
406
407 # Install dependencies
408 npm install @modelcontextprotocol/server zod
409 npm install -D @types/node typescript
410
411 # Create our files
412 md src
413 new-item src\index.ts
414 ```
415 </CodeGroup>
416
417 Update your package.json to add type: "module" and a build script:
418
419 ```json package.json theme={null}
420 {
421 "type": "module",
422 "bin": {
423 "weather": "./build/index.js"
424 },
425 "scripts": {
426 "build": "tsc && chmod 755 build/index.js"
427 },
428 "files": ["build"]
1862 },
1863 required: ["latitude", "longitude"]
1864 )
1865
1866 def self.call(latitude:, longitude:)
1867 # First get the forecast grid endpoint.
1868 points_url = "#{NWS_API_BASE}/points/#{latitude},#{longitude}"
1869 points_data = make_nws_request(points_url)
1870
1871 # Get the forecast URL from the points response.
1872 forecast_url = points_data["properties"]["forecast"]
1873 forecast_data = make_nws_request(forecast_url)
1874
1875 # Format the periods into a readable forecast.
1876 periods = forecast_data["properties"]["periods"]
1877 forecasts = periods.first(5).map do |period|
1878 <<~FORECAST
1879 #{period["name"]}:
1880 Temperature: #{period["temperature"]}°#{period["temperatureUnit"]}
1881 Wind: #{period["windSpeed"]} #{period["windDirection"]}
1882 Forecast: #{period["detailedForecast"]}
1883 FORECAST
1884 end
1885
1886 MCP::Tool::Response.new([{
1887 type: "text",
1888 text: forecasts.join("\n---\n")
1889 }])
1890 end
1891end
1892```
1893
1894### Running the server
1895
1896Finally, initialize and run the server:
1897
1898```ruby theme={null}
1899server = MCP::Server.new(
1900 name: "weather",
1901 version: "1.0.0",
1902 tools: [GetAlerts, GetForecast]
1903)
1904
1905transport = MCP::Server::Transports::StdioTransport.new(server)
1906transport.open
1907```
1908
1909Your server is complete! Run `bundle exec ruby weather.rb` to start the MCP server, which will listen for messages from MCP hosts.
1910
1911Let's now test your server from an existing MCP host, Claude for Desktop.
1912
1913## Testing your server with Claude for Desktop
1914
1915First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1916
1917We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1918
1919For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1920
1921```bash Linux theme={null}
1922code ~/.config/Claude/claude_desktop_config.json
1923```
1924
1925```bash macOS theme={null}
1926code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1927```
1928
1929```powershell Windows theme={null}
1930code $env:AppData\Claude\claude_desktop_config.json
1931```
1932
1933You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1934
1935In this case, we'll add our single weather server like so:
1936
1937```json macOS/Linux theme={null}
1938{
1939 "mcpServers": {
1940 "weather": {
1941 "command": "bundle",
1942 "args": ["exec", "ruby", "weather.rb"],
1943 "cwd": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather"
4291944 }
430 ```
431
432 Create a `tsconfig.json` in the root of your project:
433
434 ```json tsconfig.json theme={null}
435 {
436 "compilerOptions": {
437 "target": "ES2022",
438 "module": "Node16",
439 "moduleResolution": "Node16",
440 "types": ["node"],
441 "outDir": "./build",
442 "rootDir": "./src",
443 "strict": true,
444 "esModuleInterop": true,
445 "skipLibCheck": true,
446 "forceConsistentCasingInFileNames": true
447 },
448 "include": ["src/**/*"],
449 "exclude": ["node_modules"]
1945 }
1946}
1947```
1948
1949```json Windows theme={null}
1950{
1951 "mcpServers": {
1952 "weather": {
1953 "command": "bundle",
1954 "args": ["exec", "ruby", "weather.rb"],
1955 "cwd": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather"
4501956 }
451 ```
452
453 Now let's dive into building your server.
454
455 ## Building your server
456
457 ### Importing packages and setting up constants
458
459 Add these to the top of your `src/index.ts`:
460
461 ```typescript theme={null}
462 import { McpServer } from "@modelcontextprotocol/server";
463 import { serveStdio } from "@modelcontextprotocol/server/stdio";
464 import { z } from "zod";
465
466 const NWS_API_BASE = "https://api.weather.gov";
467 const USER_AGENT = "weather-app/1.0";
468 ```
469
470 ### Helper functions
471
472 Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
473
474 ```typescript theme={null}
475 // Helper function for making NWS API requests
476 async function makeNWSRequest<T>(url: string): Promise<T | null> {
477 const headers = {
478 "User-Agent": USER_AGENT,
479 Accept: "application/geo+json",
480 };
481
482 try {
483 const response = await fetch(url, { headers });
484 if (!response.ok) {
485 throw new Error(`HTTP error! status: ${response.status}`);
486 }
487 return (await response.json()) as T;
488 } catch (error) {
489 console.error("Error making NWS request:", error);
490 return null;
491 }
492 }
493
494 interface AlertFeature {
495 properties: {
496 event?: string;
497 areaDesc?: string;
498 severity?: string;
499 status?: string;
500 headline?: string;
501 };
502 }
503
504 // Format alert data
505 function formatAlert(feature: AlertFeature): string {
506 const props = feature.properties;
507 return [
508 `Event: ${props.event || "Unknown"}`,
509 `Area: ${props.areaDesc || "Unknown"}`,
510 `Severity: ${props.severity || "Unknown"}`,
511 `Status: ${props.status || "Unknown"}`,
512 `Headline: ${props.headline || "No headline"}`,
513 "---",
514 ].join("\n");
515 }
516
517 interface ForecastPeriod {
518 name?: string;
519 temperature?: number;
520 temperatureUnit?: string;
521 windSpeed?: string;
522 windDirection?: string;
523 shortForecast?: string;
524 }
525
526 interface AlertsResponse {
527 features: AlertFeature[];
528 }
529
530 interface PointsResponse {
531 properties: {
532 forecast?: string;
533 };
534 }
535
536 interface ForecastResponse {
537 properties: {
538 periods: ForecastPeriod[];
539 };
540 }
541 ```
542
543 ### Implementing tool execution
544
545 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it, inside a `createServer()` function that builds the server instance and registers both tools on it:
546
547 ```typescript theme={null}
548 // Build a server instance and register its tools. serveStdio calls this
549 // whenever it needs an instance, so every call must return a fresh one.
550 function createServer() {
551 const server = new McpServer({
552 name: "weather",
553 version: "1.0.0",
554 });
555
556 server.registerTool(
557 "get_alerts",
558 {
559 description: "Get weather alerts for a state",
560 inputSchema: z.object({
561 state: z
562 .string()
563 .length(2)
564 .describe("Two-letter state code (e.g. CA, NY)"),
565 }),
566 },
567 async ({ state }) => {
568 const stateCode = state.toUpperCase();
569 const alertsUrl = `${NWS_API_BASE}/alerts?area=${stateCode}`;
570 const alertsData = await makeNWSRequest<AlertsResponse>(alertsUrl);
571
572 if (!alertsData) {
573 return {
574 content: [
575 {
576 type: "text",
577 text: "Failed to retrieve alerts data",
578 },
579 ],
580 };
581 }
582
583 const features = alertsData.features || [];
584 if (!features.length) {
585 return {
586 content: [
587 {
588 type: "text",
589 text: `No active alerts for ${stateCode}`,
590 },
591 ],
592 };
593 }
594
595 const formattedAlerts = features.map(formatAlert);
596 const alertsText = `Active alerts for ${stateCode}:\n\n${formattedAlerts.join("\n")}`;
597
598 return {
599 content: [
600 {
601 type: "text",
602 text: alertsText,
603 },
604 ],
605 };
606 },
607 );
608
609 server.registerTool(
610 "get_forecast",
611 {
612 description: "Get weather forecast for a location",
613 inputSchema: z.object({
614 latitude: z
615 .number()
616 .min(-90)
617 .max(90)
618 .describe("Latitude of the location"),
619 longitude: z
620 .number()
621 .min(-180)
622 .max(180)
623 .describe("Longitude of the location"),
624 }),
625 },
626 async ({ latitude, longitude }) => {
627 // Get grid point data
628 const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`;
629 const pointsData = await makeNWSRequest<PointsResponse>(pointsUrl);
630
631 if (!pointsData) {
632 return {
633 content: [
634 {
635 type: "text",
636 text: `Failed to retrieve grid point data for coordinates: ${latitude}, ${longitude}. This location may not be supported by the NWS API (only US locations are supported).`,
637 },
638 ],
639 };
640 }
641
642 const forecastUrl = pointsData.properties?.forecast;
643 if (!forecastUrl) {
644 return {
645 content: [
646 {
647 type: "text",
648 text: "Failed to get forecast URL from grid point data",
649 },
650 ],
651 };
652 }
653
654 // Get forecast data
655 const forecastData = await makeNWSRequest<ForecastResponse>(forecastUrl);
656 if (!forecastData) {
657 return {
658 content: [
659 {
660 type: "text",
661 text: "Failed to retrieve forecast data",
662 },
663 ],
664 };
665 }
666
667 const periods = forecastData.properties?.periods || [];
668 if (periods.length === 0) {
669 return {
670 content: [
671 {
672 type: "text",
673 text: "No forecast periods available",
674 },
675 ],
676 };
677 }
678
679 // Format forecast periods
680 const formattedForecast = periods.map((period: ForecastPeriod) =>
681 [
682 `${period.name || "Unknown"}:`,
683 `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
684 `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
685 `${period.shortForecast || "No forecast available"}`,
686 "---",
687 ].join("\n"),
688 );
689
690 const forecastText = `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join("\n")}`;
691
692 return {
693 content: [
694 {
695 type: "text",
696 text: forecastText,
697 },
698 ],
699 };
700 },
701 );
702
703 return server;
704 }
705 ```
706
707 ### Running the server
708
709 Finally, serve the server over stdio:
710
711 ```typescript theme={null}
712 serveStdio(createServer, {
713 onerror: (error) => console.error("Weather MCP Server error:", error),
714 });
715 console.error("Weather MCP Server running on stdio");
716 ```
717
718 `serveStdio` negotiates the protocol revision with each client, so the same server answers both 2026-07-28 clients and clients that still open with the 2025-era `initialize` handshake. It calls `createServer()` whenever it needs an instance, including once for a `server/discover` probe that is discarded if the client falls back to `initialize`, which is why the factory returns a new `McpServer` on every call. Wiring the server by hand with `server.connect(new StdioServerTransport())` still compiles, but a server started that way only serves 2025-era clients.
719
720 Make sure to run `npm run build` to build your server! This is a very important step in getting your server to connect.
721
722 To check that the server answers 2026-07-28 clients, list its tools with the [Inspector CLI](/docs/2026-07-28/tools/inspector/cli) in the `modern` [protocol era](/docs/2026-07-28/tools/inspector/protocol-eras):
723
724 ```bash theme={null}
725 npx @modelcontextprotocol/inspector --cli node build/index.js --protocol-era modern --method tools/list
726 ```
727
728 The Inspector defaults to the `legacy` era, which only exercises the 2025-era handshake, so run the same command once more with `--protocol-era legacy`. Both runs list `get_alerts` and `get_forecast`.
729
730 Let's now test your server from an existing MCP host, Claude for Desktop.
731
732 ## Testing your server with Claude for Desktop
733
734 First, make sure you have Claude for Desktop installed. [You can install the latest version
735 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
736
737 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
738
739 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
740
741 <CodeGroup>
742 ```bash Linux theme={null}
743 code ~/.config/Claude/claude_desktop_config.json
744 ```
745
746 ```bash macOS theme={null}
747 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
748 ```
749
750 ```powershell Windows theme={null}
751 code $env:AppData\Claude\claude_desktop_config.json
752 ```
753 </CodeGroup>
754
755 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
756
757 In this case, we'll add our single weather server like so:
758
759 <CodeGroup>
760 ```json macOS/Linux theme={null}
761 {
762 "mcpServers": {
763 "weather": {
764 "command": "node",
765 "args": ["/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js"]
766 }
767 }
768 }
769 ```
770
771 ```json Windows theme={null}
772 {
773 "mcpServers": {
774 "weather": {
775 "command": "node",
776 "args": ["C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\index.js"]
777 }
778 }
779 }
780 ```
781 </CodeGroup>
782
783 This tells Claude for Desktop:
784
785 1. There's an MCP server named "weather"
786 2. Launch it by running `node /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/index.js`
787
788 Save the file, and restart **Claude for Desktop**.
789 </Tab>
790
791 <Tab title="Java">
792 <Note>
793 This is a quickstart demo based on Spring AI MCP auto-configuration and boot starters.
794 To learn how to create sync and async MCP Servers, manually, consult the [Java SDK Server](https://java.sdk.modelcontextprotocol.io/) documentation.
795 </Note>
796
797 Let's get started with building our weather server!
798 [You can find the complete code for what we'll be building here.](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-stdio-server)
799
800 For more information, see the [MCP Server Boot Starter](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html) reference documentation.
801 For manual MCP Server implementation, refer to the [MCP Server Java SDK documentation](https://java.sdk.modelcontextprotocol.io/).
802
803 ### Logging in MCP Servers
804
805 When implementing MCP servers, be careful about how you handle logging:
806
807 **For STDIO-based servers:** Never use `System.out.println()` or `System.out.print()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
808
809 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
810
811 ### Best Practices
812
813 * Use a logging library that writes to stderr or files.
814 * Ensure any configured logging library will not write to stdout.
815
816 ### System requirements
817
818 * Java 17 or higher installed.
819 * [Spring Boot 3.3.x](https://docs.spring.io/spring-boot/installing.html) or higher
820
821 ### Set up your environment
822
823 Use the [Spring Initializer](https://start.spring.io/) to bootstrap the project.
824
825 You will need to add the following dependencies:
826
827 <CodeGroup>
828 ```xml Maven theme={null}
829 <dependencies>
830 <dependency>
831 <groupId>org.springframework.ai</groupId>
832 <artifactId>spring-ai-starter-mcp-server</artifactId>
833 </dependency>
834
835 <dependency>
836 <groupId>org.springframework</groupId>
837 <artifactId>spring-web</artifactId>
838 </dependency>
839 </dependencies>
840 ```
841
842 ```groovy Gradle theme={null}
843 dependencies {
844 implementation platform("org.springframework.ai:spring-ai-starter-mcp-server")
845 implementation platform("org.springframework:spring-web")
846 }
847 ```
848 </CodeGroup>
849
850 Then configure your application by setting the application properties:
851
852 <CodeGroup>
853 ```bash application.properties theme={null}
854 spring.main.bannerMode=off
855 logging.pattern.console=
856 ```
857
858 ```yaml application.yml theme={null}
859 logging:
860 pattern:
861 console:
862 spring:
863 main:
864 banner-mode: off
865 ```
866 </CodeGroup>
867
868 The [Server Configuration Properties](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-server-boot-starter-docs.html#_configuration_properties) documents all available properties.
869
870 Now let's dive into building your server.
871
872 ## Building your server
873
874 ### Weather Service
875
876 Let's implement a [WeatherService.java](https://github.com/spring-projects/spring-ai-examples/blob/main/model-context-protocol/weather/starter-stdio-server/src/main/java/org/springframework/ai/mcp/sample/server/WeatherService.java) that uses a REST client to query the data from the National Weather Service API:
877
878 ```java theme={null}
879 @Service
880 public class WeatherService {
881
882 private final RestClient restClient;
883
884 public WeatherService() {
885 this.restClient = RestClient.builder()
886 .baseUrl("https://api.weather.gov")
887 .defaultHeader("Accept", "application/geo+json")
888 .defaultHeader("User-Agent", "WeatherApiClient/1.0 ([email protected])")
889 .build();
890 }
891
892 @Tool(description = "Get weather forecast for a specific latitude/longitude")
893 public String getWeatherForecastByLocation(
894 double latitude, // Latitude coordinate
895 double longitude // Longitude coordinate
896 ) {
897 // Returns detailed forecast including:
898 // - Temperature and unit
899 // - Wind speed and direction
900 // - Detailed forecast description
901 }
902
903 @Tool(description = "Get weather alerts for a US state")
904 public String getAlerts(
905 @ToolParam(description = "Two-letter US state code (e.g. CA, NY)") String state
906 ) {
907 // Returns active alerts including:
908 // - Event type
909 // - Affected area
910 // - Severity
911 // - Description
912 // - Safety instructions
913 }
914
915 // ......
916 }
917 ```
918
919 The `@Service` annotation will auto-register the service in your application context.
920 The Spring AI `@Tool` annotation makes it easy to create and maintain MCP tools.
921
922 The auto-configuration will automatically register these tools with the MCP server.
923
924 ### Create your Boot Application
925
926 ```java theme={null}
927 @SpringBootApplication
928 public class McpServerApplication {
929
930 public static void main(String[] args) {
931 SpringApplication.run(McpServerApplication.class, args);
932 }
933
934 @Bean
935 public ToolCallbackProvider weatherTools(WeatherService weatherService) {
936 return MethodToolCallbackProvider.builder().toolObjects(weatherService).build();
937 }
938 }
939 ```
940
941 Uses the `MethodToolCallbackProvider` utils to convert the `@Tools` into actionable callbacks used by the MCP server.
942
943 ### Running the server
944
945 Finally, let's build the server:
946
947 ```bash theme={null}
948 ./mvnw clean install
949 ```
950
951 This will generate an `mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar` file within the `target` folder.
952
953 Let's now test your server from an existing MCP host, Claude for Desktop.
954
955 ## Testing your server with Claude for Desktop
956
957 First, make sure you have Claude for Desktop installed.
958 [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
959
960 We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
961 To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
962 Make sure to create the file if it doesn't exist.
963
964 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
965
966 <CodeGroup>
967 ```bash Linux theme={null}
968 code ~/.config/Claude/claude_desktop_config.json
969 ```
970
971 ```bash macOS theme={null}
972 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
973 ```
974
975 ```powershell Windows theme={null}
976 code $env:AppData\Claude\claude_desktop_config.json
977 ```
978 </CodeGroup>
979
980 You'll then add your servers in the `mcpServers` key.
981 The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
982
983 In this case, we'll add our single weather server like so:
984
985 <CodeGroup>
986 ```json macOS/Linux theme={null}
987 {
988 "mcpServers": {
989 "spring-ai-mcp-weather": {
990 "command": "java",
991 "args": [
992 "-Dspring.ai.mcp.server.stdio=true",
993 "-jar",
994 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
995 ]
996 }
997 }
998 }
999 ```
1000
1001 ```json Windows theme={null}
1002 {
1003 "mcpServers": {
1004 "spring-ai-mcp-weather": {
1005 "command": "java",
1006 "args": [
1007 "-Dspring.ai.mcp.server.transport=STDIO",
1008 "-jar",
1009 "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar"
1010 ]
1011 }
1012 }
1013 }
1014 ```
1015 </CodeGroup>
1016
1017 <Note>
1018 Make sure you pass in the absolute path to your server.
1019 </Note>
1020
1021 This tells Claude for Desktop:
1022
1023 1. There's an MCP server named "my-weather-server"
1024 2. To launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar`
1025
1026 Save the file, and restart **Claude for Desktop**.
1027
1028 ## Testing your server with Java client
1029
1030 ### Create an MCP Client manually
1031
1032 Use the `McpClient` to connect to the server:
1033
1034 ```java theme={null}
1035 var stdioParams = ServerParameters.builder("java")
1036 .args("-jar", "/ABSOLUTE/PATH/TO/PARENT/FOLDER/mcp-weather-stdio-server-0.0.1-SNAPSHOT.jar")
1037 .build();
1038
1039 var stdioTransport = new StdioClientTransport(stdioParams);
1040
1041 var mcpClient = McpClient.sync(stdioTransport).build();
1042
1043 mcpClient.initialize();
1044
1045 ListToolsResult toolsList = mcpClient.listTools();
1046
1047 CallToolResult weather = mcpClient.callTool(
1048 new CallToolRequest("getWeatherForecastByLocation",
1049 Map.of("latitude", "47.6062", "longitude", "-122.3321")));
1050
1051 CallToolResult alert = mcpClient.callTool(
1052 new CallToolRequest("getAlerts", Map.of("state", "NY")));
1053
1054 mcpClient.closeGracefully();
1055 ```
1056
1057 ### Use MCP Client Boot Starter
1058
1059 Create a new boot starter application using the `spring-ai-starter-mcp-client` dependency:
1060
1061 ```xml theme={null}
1062 <dependency>
1063 <groupId>org.springframework.ai</groupId>
1064 <artifactId>spring-ai-starter-mcp-client</artifactId>
1065 </dependency>
1066 ```
1067
1068 and set the `spring.ai.mcp.client.stdio.servers-configuration` property to point to your `claude_desktop_config.json`.
1069 You can reuse the existing Anthropic Desktop configuration:
1070
1071 ```properties theme={null}
1072 spring.ai.mcp.client.stdio.servers-configuration=file:PATH/TO/claude_desktop_config.json
1073 ```
1074
1075 When you start your client application, the auto-configuration will automatically create MCP clients from the claude\_desktop\_config.json.
1076
1077 For more information, see the [MCP Client Boot Starters](https://docs.spring.io/spring-ai/reference/api/mcp/mcp-client-boot-starter-docs.html) reference documentation.
1078
1079 ## More Java MCP Server examples
1080
1081 The [starter-webflux-server](https://github.com/spring-projects/spring-ai-examples/tree/main/model-context-protocol/weather/starter-webflux-server) demonstrates how to create an HTTP-based MCP server with the WebFlux starter.
1082 Set the `spring.ai.mcp.server.protocol=STREAMABLE` property to serve it over Streamable HTTP.
1083 It showcases how to define and register MCP Tools, Resources, and Prompts, using the Spring Boot's auto-configuration capabilities.
1084 </Tab>
1085
1086 <Tab title="Kotlin">
1087 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/kotlin-sdk/tree/main/samples/weather-stdio-server)
1088
1089 ### Prerequisite knowledge
1090
1091 This quickstart assumes you have familiarity with:
1092
1093 * Kotlin
1094 * LLMs like Claude
1095
1096 ### Logging in MCP Servers
1097
1098 When implementing MCP servers, be careful about how you handle logging:
1099
1100 **For STDIO-based servers:** Never use `println()`, as it writes to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1101
1102 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1103
1104 ### Best Practices
1105
1106 * Use a logging library that writes to stderr or files.
1107
1108 ### System requirements
1109
1110 * JDK 11 or higher installed.
1111
1112 ### Set up your environment
1113
1114 First, let's install `java` and `gradle` if you haven't already.
1115 You can download `java` from [official Oracle JDK website](https://www.oracle.com/java/technologies/downloads/).
1116 Verify your `java` installation:
1117
1118 ```bash theme={null}
1119 java --version
1120 ```
1121
1122 Now, let's create and set up your project:
1123
1124 <CodeGroup>
1125 ```bash macOS/Linux theme={null}
1126 # Create a new directory for our project
1127 mkdir weather
1128 cd weather
1129
1130 # Initialize a new kotlin project
1131 gradle init
1132 ```
1133
1134 ```powershell Windows theme={null}
1135 # Create a new directory for our project
1136 md weather
1137 cd weather
1138
1139 # Initialize a new kotlin project
1140 gradle init
1141 ```
1142 </CodeGroup>
1143
1144 After running `gradle init`, select **Application** as the project type, **Kotlin** as the programming language.
1145
1146 Alternatively, you can create a Kotlin application using the [IntelliJ IDEA project wizard](https://kotlinlang.org/docs/jvm-get-started.html).
1147
1148 After creating the project, replace the contents of your `build.gradle.kts` with:
1149
1150 ```kotlin build.gradle.kts theme={null}
1151 // Check latest versions at https://github.com/modelcontextprotocol/kotlin-sdk/releases
1152 val mcpVersion = "0.9.0"
1153 val ktorVersion = "3.2.3"
1154 val slf4jVersion = "2.0.17"
1155
1156 plugins {
1157 kotlin("jvm") version "2.3.20"
1158 kotlin("plugin.serialization") version "2.3.20"
1159 id("com.gradleup.shadow") version "8.3.9"
1160 application
1161 }
1162
1163 application {
1164 mainClass.set("MainKt")
1165 }
1166
1167 dependencies {
1168 implementation("io.modelcontextprotocol:kotlin-sdk:$mcpVersion")
1169 implementation("io.ktor:ktor-client-content-negotiation:$ktorVersion")
1170 implementation("io.ktor:ktor-serialization-kotlinx-json:$ktorVersion")
1171 implementation("io.ktor:ktor-client-cio:$ktorVersion")
1172 implementation("org.slf4j:slf4j-simple:$slf4jVersion")
1173 }
1174 ```
1175
1176 Verify that everything is set up correctly:
1177
1178 ```bash theme={null}
1179 ./gradlew build
1180 ```
1181
1182 Now let's dive into building your server.
1183
1184 ## Building your server
1185
1186 ### Setting up the instance
1187
1188 Add a server initialization function:
1189
1190 ```kotlin theme={null}
1191 fun runMcpServer() {
1192 val server = Server(
1193 Implementation(
1194 name = "weather",
1195 version = "1.0.0",
1196 ),
1197 ServerOptions(
1198 capabilities = ServerCapabilities(tools = ServerCapabilities.Tools(listChanged = true)),
1199 ),
1200 )
1201
1202 // register tools on server here
1203
1204 val transport = StdioServerTransport(
1205 System.`in`.asInput(),
1206 System.out.asSink().buffered(),
1207 )
1208
1209 runBlocking {
1210 val session = server.createSession(transport)
1211 val done = Job()
1212 session.onClose {
1213 done.complete()
1214 }
1215 done.join()
1957 }
1958}
1959```
1960
1961> [!NOTE]
1962>
1963> Make sure you pass in the absolute path to your project directory in the `cwd` field. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
1964
1965This tells Claude for Desktop:
1966
19671. There's an MCP server named "weather"
19682. Launch it by running `bundle exec ruby weather.rb` in the specified directory
1969
1970Save the file, and restart **Claude for Desktop**.
1971
1972**Rust**
1973
1974Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust)
1975
1976### Prerequisite knowledge
1977
1978This quickstart assumes you have familiarity with:
1979
1980* Rust programming language
1981* Async/await in Rust
1982* LLMs like Claude
1983
1984### Logging in MCP Servers
1985
1986When implementing MCP servers, be careful about how you handle logging:
1987
1988**For STDIO-based servers:** Never use `println!()` or `print!()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
1989
1990**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1991
1992### Best Practices
1993
1994* Use a logging library that writes to stderr or files, such as `tracing` or `log` in Rust.
1995* Configure your logging framework to avoid stdout output.
1996
1997### Quick Examples
1998
1999```rust theme={null}
2000// ❌ Bad (STDIO)
2001println!("Processing request");
2002
2003// ✅ Good (STDIO)
2004eprintln!("Processing request"); // writes to stderr
2005```
2006
2007### System requirements
2008
2009* Rust 1.70 or higher installed.
2010* Cargo (comes with Rust installation).
2011
2012### Set up your environment
2013
2014First, let's install Rust if you haven't already. You can install Rust from [rust-lang.org](https://www.rust-lang.org/tools/install):
2015
2016```bash macOS/Linux theme={null}
2017curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
2018```
2019
2020```powershell Windows theme={null}
2021# Download and run rustup-init.exe from https://rustup.rs/
2022```
2023
2024Verify your Rust installation:
2025
2026```bash theme={null}
2027rustc --version
2028cargo --version
2029```
2030
2031Now, let's create and set up our project:
2032
2033```bash macOS/Linux theme={null}
2034# Create a new Rust project
2035cargo new weather
2036cd weather
2037```
2038
2039```powershell Windows theme={null}
2040# Create a new Rust project
2041cargo new weather
2042cd weather
2043```
2044
2045Update your `Cargo.toml` to add the required dependencies:
2046
2047```toml Cargo.toml theme={null}
2048[package]
2049name = "weather"
2050version = "0.1.0"
2051edition = "2024"
2052
2053[dependencies]
2054rmcp = { version = "0.3", features = ["server", "macros", "transport-io"] }
2055tokio = { version = "1.46", features = ["full"] }
2056reqwest = { version = "0.12", features = ["json"] }
2057serde = { version = "1.0", features = ["derive"] }
2058serde_json = "1.0"
2059anyhow = "1.0"
2060tracing = "0.1"
2061tracing-subscriber = { version = "0.3", features = ["env-filter", "std", "fmt"] }
2062```
2063
2064Now let's dive into building your server.
2065
2066## Building your server
2067
2068### Importing packages and constants
2069
2070Open `src/main.rs` and add these imports and constants at the top:
2071
2072```rust theme={null}
2073use anyhow::Result;
2074use rmcp::{
2075 ServerHandler, ServiceExt,
2076 handler::server::{router::tool::ToolRouter, tool::Parameters},
2077 model::*,
2078 schemars, tool, tool_handler, tool_router,
2079};
2080use serde::Deserialize;
2081use serde::de::DeserializeOwned;
2082
2083const NWS_API_BASE: &str = "https://api.weather.gov";
2084const USER_AGENT: &str = "weather-app/1.0";
2085```
2086
2087The `rmcp` crate provides the Model Context Protocol SDK for Rust, with features for server implementation, procedural macros, and stdio transport.
2088
2089### Data structures
2090
2091Next, let's define the data structures for deserializing responses from the National Weather Service API:
2092
2093```rust theme={null}
2094#[derive(Debug, Deserialize)]
2095struct AlertsResponse {
2096 features: Vec<AlertFeature>,
2097}
2098
2099#[derive(Debug, Deserialize)]
2100struct AlertFeature {
2101 properties: AlertProperties,
2102}
2103
2104#[derive(Debug, Deserialize)]
2105struct AlertProperties {
2106 event: Option<String>,
2107 #[serde(rename = "areaDesc")]
2108 area_desc: Option<String>,
2109 severity: Option<String>,
2110 description: Option<String>,
2111 instruction: Option<String>,
2112}
2113
2114#[derive(Debug, Deserialize)]
2115struct PointsResponse {
2116 properties: PointsProperties,
2117}
2118
2119#[derive(Debug, Deserialize)]
2120struct PointsProperties {
2121 forecast: String,
2122}
2123
2124#[derive(Debug, Deserialize)]
2125struct ForecastResponse {
2126 properties: ForecastProperties,
2127}
2128
2129#[derive(Debug, Deserialize)]
2130struct ForecastProperties {
2131 periods: Vec<ForecastPeriod>,
2132}
2133
2134#[derive(Debug, Deserialize)]
2135struct ForecastPeriod {
2136 name: String,
2137 temperature: i32,
2138 #[serde(rename = "temperatureUnit")]
2139 temperature_unit: String,
2140 #[serde(rename = "windSpeed")]
2141 wind_speed: String,
2142 #[serde(rename = "windDirection")]
2143 wind_direction: String,
2144 #[serde(rename = "detailedForecast")]
2145 detailed_forecast: String,
2146}
2147```
2148
2149Now define the request types that MCP clients will send:
2150
2151```rust theme={null}
2152#[derive(serde::Deserialize, schemars::JsonSchema)]
2153pub struct MCPForecastRequest {
2154 latitude: f32,
2155 longitude: f32,
2156}
2157
2158#[derive(serde::Deserialize, schemars::JsonSchema)]
2159pub struct MCPAlertRequest {
2160 state: String,
2161}
2162```
2163
2164### Helper functions
2165
2166Add helper functions for making API requests and formatting responses:
2167
2168```rust theme={null}
2169async fn make_nws_request<T: DeserializeOwned>(url: &str) -> Result<T> {
2170 let client = reqwest::Client::new();
2171 let rsp = client
2172 .get(url)
2173 .header(reqwest::header::USER_AGENT, USER_AGENT)
2174 .header(reqwest::header::ACCEPT, "application/geo+json")
2175 .send()
2176 .await?
2177 .error_for_status()?;
2178 Ok(rsp.json::<T>().await?)
2179}
2180
2181fn format_alert(feature: &AlertFeature) -> String {
2182 let props = &feature.properties;
2183 format!(
2184 "Event: {}\nArea: {}\nSeverity: {}\nDescription: {}\nInstructions: {}",
2185 props.event.as_deref().unwrap_or("Unknown"),
2186 props.area_desc.as_deref().unwrap_or("Unknown"),
2187 props.severity.as_deref().unwrap_or("Unknown"),
2188 props
2189 .description
2190 .as_deref()
2191 .unwrap_or("No description available"),
2192 props
2193 .instruction
2194 .as_deref()
2195 .unwrap_or("No specific instructions provided")
2196 )
2197}
2198
2199fn format_period(period: &ForecastPeriod) -> String {
2200 format!(
2201 "{}:\nTemperature: {}°{}\nWind: {} {}\nForecast: {}",
2202 period.name,
2203 period.temperature,
2204 period.temperature_unit,
2205 period.wind_speed,
2206 period.wind_direction,
2207 period.detailed_forecast
2208 )
2209}
2210```
2211
2212### Implementing the Weather server and tools
2213
2214Now let's implement the main Weather server struct with the tool handlers:
2215
2216```rust theme={null}
2217pub struct Weather {
2218 tool_router: ToolRouter<Weather>,
2219}
2220
2221#[tool_router]
2222impl Weather {
2223 fn new() -> Self {
2224 Self {
2225 tool_router: Self::tool_router(),
12162226 }
12172227 }
1218 ```
1219
1220 ### Weather API helper functions
1221
1222 Next, let's add functions and data classes for querying and converting responses from the National Weather Service API:
1223
1224 ```kotlin theme={null}
1225 val httpClient = HttpClient(CIO) {
1226 defaultRequest {
1227 url("https://api.weather.gov")
1228 headers {
1229 append("Accept", "application/geo+json")
1230 append("User-Agent", "WeatherApiClient/1.0")
2228
2229 #[tool(description = "Get weather alerts for a US state.")]
2230 async fn get_alerts(
2231 &self,
2232 Parameters(MCPAlertRequest { state }): Parameters<MCPAlertRequest>,
2233 ) -> String {
2234 let url = format!(
2235 "{}/alerts/active/area/{}",
2236 NWS_API_BASE,
2237 state.to_uppercase()
2238 );
2239
2240 match make_nws_request::<AlertsResponse>(&url).await {
2241 Ok(data) => {
2242 if data.features.is_empty() {
2243 "No active alerts for this state.".to_string()
2244 } else {
2245 data.features
2246 .iter()
2247 .map(format_alert)
2248 .collect::<Vec<_>>()
2249 .join("\n---\n")
2250 }
12312251 }
1232 contentType(ContentType.Application.Json)
1233 }
1234 install(ContentNegotiation) {
1235 json(Json { ignoreUnknownKeys = true })
2252 Err(_) => "Unable to fetch alerts or no alerts found.".to_string(),
12362253 }
12372254 }
12382255
1239 // Extension function to fetch weather alerts for a given state
1240 suspend fun HttpClient.getAlerts(state: String): List<String> {
1241 val alerts = this.get("/alerts/active/area/$state").body<AlertsResponse>()
1242 return alerts.features.map { feature ->
1243 """
1244 Event: ${feature.properties.event}
1245 Area: ${feature.properties.areaDesc}
1246 Severity: ${feature.properties.severity}
1247 Status: ${feature.properties.status}
1248 Headline: ${feature.properties.headline}
1249 """.trimIndent()
2256 #[tool(description = "Get weather forecast for a location.")]
2257 async fn get_forecast(
2258 &self,
2259 Parameters(MCPForecastRequest {
2260 latitude,
2261 longitude,
2262 }): Parameters<MCPForecastRequest>,
2263 ) -> String {
2264 let points_url = format!("{NWS_API_BASE}/points/{latitude},{longitude}");
2265 let Ok(points_data) = make_nws_request::<PointsResponse>(&points_url).await else {
2266 return "Unable to fetch forecast data for this location.".to_string();
2267 };
2268
2269 let forecast_url = points_data.properties.forecast;
2270
2271 let Ok(forecast_data) = make_nws_request::<ForecastResponse>(&forecast_url).await else {
2272 return "Unable to fetch forecast data for this location.".to_string();
2273 };
2274
2275 let periods = &forecast_data.properties.periods;
2276 let forecast_summary: String = periods
2277 .iter()
2278 .take(5) // Next 5 periods only
2279 .map(format_period)
2280 .collect::<Vec<String>>()
2281 .join("\n---\n");
2282 forecast_summary
2283 }
2284}
2285```
2286
2287The `#[tool_router]` macro automatically generates the routing logic, and the `#[tool]` attribute marks methods as MCP tools.
2288
2289### Implementing the ServerHandler
2290
2291Implement the `ServerHandler` trait to define server capabilities:
2292
2293```rust theme={null}
2294#[tool_handler]
2295impl ServerHandler for Weather {
2296 fn get_info(&self) -> ServerInfo {
2297 ServerInfo {
2298 capabilities: ServerCapabilities::builder().enable_tools().build(),
2299 ..Default::default()
12502300 }
12512301 }
1252
1253 // Extension function to fetch forecast information for given latitude and longitude
1254 suspend fun HttpClient.getForecast(latitude: Double, longitude: Double): List<String> {
1255 val points = this.get("/points/$latitude,$longitude").body<PointsResponse>()
1256 val forecastUrl = points.properties.forecast ?: error("No forecast URL available")
1257 val forecast = this.get(forecastUrl).body<ForecastResponse>()
1258 return forecast.properties.periods.map { period ->
1259 """
1260 ${period.name}:
1261 Temperature: ${period.temperature}°${period.temperatureUnit}
1262 Wind: ${period.windSpeed} ${period.windDirection}
1263 ${period.shortForecast}
1264 """.trimIndent()
1265 }
2302}
2303```
2304
2305### Running the server
2306
2307Finally, implement the main function to run the server with stdio transport:
2308
2309```rust theme={null}
2310#[tokio::main]
2311async fn main() -> Result<()> {
2312 let transport = (tokio::io::stdin(), tokio::io::stdout());
2313 let service = Weather::new().serve(transport).await?;
2314 service.waiting().await?;
2315 Ok(())
2316}
2317```
2318
2319Build your server with:
2320
2321```bash theme={null}
2322cargo build --release
2323```
2324
2325The compiled binary will be in `target/release/weather`.
2326
2327Let's now test your server from an existing MCP host, Claude for Desktop.
2328
2329## Testing your server with Claude for Desktop
2330
2331First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2332
2333We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2334
2335For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2336
2337```bash Linux theme={null}
2338code ~/.config/Claude/claude_desktop_config.json
2339```
2340
2341```bash macOS theme={null}
2342code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2343```
2344
2345```powershell Windows theme={null}
2346code $env:AppData\Claude\claude_desktop_config.json
2347```
2348
2349You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2350
2351In this case, we'll add our single weather server like so:
2352
2353```json macOS/Linux theme={null}
2354{
2355 "mcpServers": {
2356 "weather": {
2357 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/target/release/weather"
12662358 }
1267
1268 @Serializable
1269 data class PointsResponse(val properties: PointsProperties)
1270
1271 @Serializable
1272 data class PointsProperties(val forecast: String? = null)
1273
1274 @Serializable
1275 data class ForecastResponse(val properties: ForecastProperties)
1276
1277 @Serializable
1278 data class ForecastProperties(val periods: List<ForecastPeriod> = emptyList())
1279
1280 @Serializable
1281 data class ForecastPeriod(
1282 val name: String? = null,
1283 val temperature: Int? = null,
1284 val temperatureUnit: String? = null,
1285 val windSpeed: String? = null,
1286 val windDirection: String? = null,
1287 val shortForecast: String? = null,
1288 )
1289
1290 @Serializable
1291 data class AlertsResponse(val features: List<AlertFeature> = emptyList())
1292
1293 @Serializable
1294 data class AlertFeature(val properties: AlertProperties)
1295
1296 @Serializable
1297 data class AlertProperties(
1298 val event: String? = null,
1299 val areaDesc: String? = null,
1300 val severity: String? = null,
1301 val status: String? = null,
1302 val headline: String? = null,
1303 )
1304 ```
1305
1306 ### Implementing tool execution
1307
1308 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
1309
1310 ```kotlin theme={null}
1311 // Register weather tools
1312
1313 server.addTool(
1314 name = "get_alerts",
1315 description = "Get weather alerts for a US state. Input is a two-letter US state code (e.g. CA, NY)",
1316 inputSchema = ToolSchema(
1317 properties = buildJsonObject {
1318 putJsonObject("state") {
1319 put("type", "string")
1320 put("description", "Two-letter US state code (e.g. CA, NY)")
1321 }
1322 },
1323 required = listOf("state"),
1324 ),
1325 ) { request ->
1326 val state = request.arguments?.get("state")?.jsonPrimitive?.content
1327 ?: return@addTool CallToolResult(
1328 content = listOf(TextContent("The 'state' parameter is required.")),
1329 )
1330
1331 val alerts = httpClient.getAlerts(state)
1332 CallToolResult(content = alerts.map { TextContent(it) })
2359 }
2360}
2361```
2362
2363```json Windows theme={null}
2364{
2365 "mcpServers": {
2366 "weather": {
2367 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\target\\release\\weather.exe"
13332368 }
1334
1335 server.addTool(
1336 name = "get_forecast",
1337 description = "Get weather forecast for a location. Note: only US locations are supported by the NWS API.",
1338 inputSchema = ToolSchema(
1339 properties = buildJsonObject {
1340 putJsonObject("latitude") {
1341 put("type", "number")
1342 put("description", "Latitude of the location")
1343 }
1344 putJsonObject("longitude") {
1345 put("type", "number")
1346 put("description", "Longitude of the location")
1347 }
1348 },
1349 required = listOf("latitude", "longitude"),
1350 ),
1351 ) { request ->
1352 val latitude = request.arguments?.get("latitude")?.jsonPrimitive?.doubleOrNull
1353 val longitude = request.arguments?.get("longitude")?.jsonPrimitive?.doubleOrNull
1354 if (latitude == null || longitude == null) {
1355 return@addTool CallToolResult(
1356 content = listOf(TextContent("The 'latitude' and 'longitude' parameters are required.")),
1357 )
1358 }
1359
1360 val forecast = httpClient.getForecast(latitude, longitude)
1361 CallToolResult(content = forecast.map { TextContent(it) })
2369 }
2370}
2371```
2372
2373> [!NOTE]
2374>
2375> Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2376
2377This tells Claude for Desktop:
2378
23791. There's an MCP server named "weather"
23802. Launch it by running the compiled binary at the specified path
2381
2382Save the file, and restart **Claude for Desktop**.
2383
2384**Go**
2385
2386Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-go)
2387
2388### Prerequisite knowledge
2389
2390This quickstart assumes you have familiarity with:
2391
2392* Go
2393* LLMs like Claude
2394
2395### Logging in MCP Servers
2396
2397When implementing MCP servers, be careful about how you handle logging:
2398
2399**For STDIO-based servers:** Never use `fmt.Println()` or `fmt.Printf()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
2400
2401**For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
2402
2403### Best Practices
2404
2405* Use `log.Println()` (which defaults to stderr) or a logging library that writes to stderr or files.
2406* Use `fmt.Fprintf(os.Stderr, ...)` to write to stderr explicitly.
2407
2408### Quick Examples
2409
2410```go theme={null}
2411// ❌ Bad (STDIO)
2412fmt.Println("Processing request")
2413
2414// ✅ Good (STDIO)
2415log.Println("Processing request") // defaults to stderr
2416
2417// ✅ Good (STDIO)
2418fmt.Fprintln(os.Stderr, "Processing request")
2419```
2420
2421### System requirements
2422
2423* Go 1.24 or higher installed.
2424
2425### Set up your environment
2426
2427First, let's install Go if you haven't already. You can download and install Go from [go.dev](https://go.dev/dl/).
2428
2429Verify your Go installation:
2430
2431```bash theme={null}
2432go version
2433```
2434
2435Now, let's create and set up our project:
2436
2437```bash macOS/Linux theme={null}
2438# Create a new directory for our project
2439mkdir weather
2440cd weather
2441
2442# Initialize Go module
2443go mod init weather
2444
2445# Install dependencies
2446go get github.com/modelcontextprotocol/go-sdk/mcp
2447
2448# Create our server file
2449touch main.go
2450```
2451
2452```powershell Windows theme={null}
2453# Create a new directory for our project
2454md weather
2455cd weather
2456
2457# Initialize Go module
2458go mod init weather
2459
2460# Install dependencies
2461go get github.com/modelcontextprotocol/go-sdk/mcp
2462
2463# Create our server file
2464new-item main.go
2465```
2466
2467Now let's dive into building your server.
2468
2469## Building your server
2470
2471### Importing packages and constants
2472
2473Add these to the top of your `main.go`:
2474
2475```go theme={null}
2476package main
2477
2478import (
2479 "cmp"
2480 "context"
2481 "encoding/json"
2482 "fmt"
2483 "io"
2484 "log"
2485 "net/http"
2486 "strings"
2487
2488 "github.com/modelcontextprotocol/go-sdk/mcp"
2489)
2490
2491const (
2492 NWSAPIBase = "https://api.weather.gov"
2493 UserAgent = "weather-app/1.0"
2494)
2495```
2496
2497### Data structures
2498
2499Next, let's define the data structures used by our tools:
2500
2501```go theme={null}
2502type PointsResponse struct {
2503 Properties struct {
2504 Forecast string `json:"forecast"`
2505 } `json:"properties"`
2506}
2507
2508type ForecastResponse struct {
2509 Properties struct {
2510 Periods []ForecastPeriod `json:"periods"`
2511 } `json:"properties"`
2512}
2513
2514type ForecastPeriod struct {
2515 Name string `json:"name"`
2516 Temperature int `json:"temperature"`
2517 TemperatureUnit string `json:"temperatureUnit"`
2518 WindSpeed string `json:"windSpeed"`
2519 WindDirection string `json:"windDirection"`
2520 DetailedForecast string `json:"detailedForecast"`
2521}
2522
2523type AlertsResponse struct {
2524 Features []AlertFeature `json:"features"`
2525}
2526
2527type AlertFeature struct {
2528 Properties AlertProperties `json:"properties"`
2529}
2530
2531type AlertProperties struct {
2532 Event string `json:"event"`
2533 AreaDesc string `json:"areaDesc"`
2534 Severity string `json:"severity"`
2535 Description string `json:"description"`
2536 Instruction string `json:"instruction"`
2537}
2538
2539type ForecastInput struct {
2540 Latitude float64 `json:"latitude" jsonschema:"Latitude of the location"`
2541 Longitude float64 `json:"longitude" jsonschema:"Longitude of the location"`
2542}
2543
2544type AlertsInput struct {
2545 State string `json:"state" jsonschema:"Two-letter US state code (e.g. CA, NY)"`
2546}
2547```
2548
2549### Helper functions
2550
2551Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
2552
2553```go theme={null}
2554func makeNWSRequest[T any](ctx context.Context, url string) (*T, error) {
2555 req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
2556 if err != nil {
2557 return nil, fmt.Errorf("failed to create request: %w", err)
2558 }
2559
2560 req.Header.Set("User-Agent", UserAgent)
2561 req.Header.Set("Accept", "application/geo+json")
2562
2563 client := http.DefaultClient
2564 resp, err := client.Do(req)
2565 if err != nil {
2566 return nil, fmt.Errorf("failed to make request to %s: %w", url, err)
2567 }
2568 defer resp.Body.Close()
2569
2570 if resp.StatusCode != http.StatusOK {
2571 body, _ := io.ReadAll(resp.Body)
2572 return nil, fmt.Errorf("HTTP error %d: %s", resp.StatusCode, string(body))
2573 }
2574
2575 var result T
2576 if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
2577 return nil, fmt.Errorf("failed to decode response: %w", err)
2578 }
2579
2580 return &result, nil
2581}
2582
2583func formatAlert(alert AlertFeature) string {
2584 props := alert.Properties
2585 event := cmp.Or(props.Event, "Unknown")
2586 areaDesc := cmp.Or(props.AreaDesc, "Unknown")
2587 severity := cmp.Or(props.Severity, "Unknown")
2588 description := cmp.Or(props.Description, "No description available")
2589 instruction := cmp.Or(props.Instruction, "No specific instructions provided")
2590
2591 return fmt.Sprintf(`
2592Event: %s
2593Area: %s
2594Severity: %s
2595Description: %s
2596Instructions: %s
2597`, event, areaDesc, severity, description, instruction)
2598}
2599
2600func formatPeriod(period ForecastPeriod) string {
2601 return fmt.Sprintf(`
2602%s:
2603Temperature: %d°%s
2604Wind: %s %s
2605Forecast: %s
2606`, period.Name, period.Temperature, period.TemperatureUnit,
2607 period.WindSpeed, period.WindDirection, period.DetailedForecast)
2608}
2609```
2610
2611### Implementing tool execution
2612
2613The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
2614
2615```go theme={null}
2616func getForecast(ctx context.Context, req *mcp.CallToolRequest, input ForecastInput) (
2617 *mcp.CallToolResult, any, error,
2618) {
2619 // Get points data
2620 pointsURL := fmt.Sprintf("%s/points/%f,%f", NWSAPIBase, input.Latitude, input.Longitude)
2621 pointsData, err := makeNWSRequest[PointsResponse](ctx, pointsURL)
2622 if err != nil {
2623 return &mcp.CallToolResult{
2624 Content: []mcp.Content{
2625 &mcp.TextContent{Text: "Unable to fetch forecast data for this location."},
2626 },
2627 }, nil, nil
2628 }
2629
2630 // Get forecast data
2631 forecastURL := pointsData.Properties.Forecast
2632 if forecastURL == "" {
2633 return &mcp.CallToolResult{
2634 Content: []mcp.Content{
2635 &mcp.TextContent{Text: "Unable to fetch forecast URL."},
2636 },
2637 }, nil, nil
2638 }
2639
2640 forecastData, err := makeNWSRequest[ForecastResponse](ctx, forecastURL)
2641 if err != nil {
2642 return &mcp.CallToolResult{
2643 Content: []mcp.Content{
2644 &mcp.TextContent{Text: "Unable to fetch detailed forecast."},
2645 },
2646 }, nil, nil
2647 }
2648
2649 // Format the periods
2650 periods := forecastData.Properties.Periods
2651 if len(periods) == 0 {
2652 return &mcp.CallToolResult{
2653 Content: []mcp.Content{
2654 &mcp.TextContent{Text: "No forecast periods available."},
2655 },
2656 }, nil, nil
2657 }
2658
2659 // Show next 5 periods
2660 var forecasts []string
2661 for i := range min(5, len(periods)) {
2662 forecasts = append(forecasts, formatPeriod(periods[i]))
2663 }
2664
2665 result := strings.Join(forecasts, "\n---\n")
2666
2667 return &mcp.CallToolResult{
2668 Content: []mcp.Content{
2669 &mcp.TextContent{Text: result},
2670 },
2671 }, nil, nil
2672}
2673
2674func getAlerts(ctx context.Context, req *mcp.CallToolRequest, input AlertsInput) (
2675 *mcp.CallToolResult, any, error,
2676) {
2677 // Build alerts URL
2678 stateCode := strings.ToUpper(input.State)
2679 alertsURL := fmt.Sprintf("%s/alerts/active/area/%s", NWSAPIBase, stateCode)
2680
2681 alertsData, err := makeNWSRequest[AlertsResponse](ctx, alertsURL)
2682 if err != nil {
2683 return &mcp.CallToolResult{
2684 Content: []mcp.Content{
2685 &mcp.TextContent{Text: "Unable to fetch alerts or no alerts found."},
2686 },
2687 }, nil, nil
2688 }
2689
2690 // Check if there are any alerts
2691 if len(alertsData.Features) == 0 {
2692 return &mcp.CallToolResult{
2693 Content: []mcp.Content{
2694 &mcp.TextContent{Text: "No active alerts for this state."},
2695 },
2696 }, nil, nil
2697 }
2698
2699 // Format alerts
2700 var alerts []string
2701 for _, feature := range alertsData.Features {
2702 alerts = append(alerts, formatAlert(feature))
2703 }
2704
2705 result := strings.Join(alerts, "\n---\n")
2706
2707 return &mcp.CallToolResult{
2708 Content: []mcp.Content{
2709 &mcp.TextContent{Text: result},
2710 },
2711 }, nil, nil
2712}
2713```
2714
2715### Running the server
2716
2717Finally, implement the main function to run the server:
2718
2719```go theme={null}
2720func main() {
2721 // Create MCP server
2722 server := mcp.NewServer(&mcp.Implementation{
2723 Name: "weather",
2724 Version: "1.0.0",
2725 }, nil)
2726
2727 // Add get_forecast tool
2728 mcp.AddTool(server, &mcp.Tool{
2729 Name: "get_forecast",
2730 Description: "Get weather forecast for a location",
2731 }, getForecast)
2732
2733 // Add get_alerts tool
2734 mcp.AddTool(server, &mcp.Tool{
2735 Name: "get_alerts",
2736 Description: "Get weather alerts for a US state",
2737 }, getAlerts)
2738
2739 // Run server on stdio transport
2740 if err := server.Run(context.Background(), &mcp.StdioTransport{}); err != nil {
2741 log.Fatal(err)
2742 }
2743}
2744```
2745
2746Build your server with:
2747
2748```bash theme={null}
2749go build -o weather .
2750```
2751
2752The compiled binary will be in `./weather`.
2753
2754Let's now test your server from an existing MCP host, Claude for Desktop.
2755
2756## Testing your server with Claude for Desktop
2757
2758First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2759
2760We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2761
2762For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2763
2764```bash Linux theme={null}
2765code ~/.config/Claude/claude_desktop_config.json
2766```
2767
2768```bash macOS theme={null}
2769code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2770```
2771
2772```powershell Windows theme={null}
2773code $env:AppData\Claude\claude_desktop_config.json
2774```
2775
2776You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2777
2778In this case, we'll add our single weather server like so:
2779
2780```json macOS/Linux theme={null}
2781{
2782 "mcpServers": {
2783 "weather": {
2784 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/weather"
13622785 }
1363 ```
1364
1365 ### Running the server
1366
1367 Finally, implement the main function to run the server:
1368
1369 ```kotlin theme={null}
1370 fun main() = runMcpServer()
1371 ```
1372
1373 You can run the server directly during development:
1374
1375 ```bash theme={null}
1376 ./gradlew run
1377 ```
1378
1379 For production use, build the shadow JAR:
1380
1381 ```bash theme={null}
1382 ./gradlew build
1383 java -jar build/libs/weather-0.1.0-all.jar
1384 ```
1385
1386 Let's now test your server from an existing MCP host, Claude for Desktop.
1387
1388 ## Testing your server with Claude for Desktop
1389
1390 First, make sure you have Claude for Desktop installed. [You can install the latest version
1391 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1392
1393 We'll need to configure Claude for Desktop for whichever MCP servers you want to use.
1394 To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor.
1395 Make sure to create the file if it doesn't exist.
1396
1397 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1398
1399 <CodeGroup>
1400 ```bash Linux theme={null}
1401 code ~/.config/Claude/claude_desktop_config.json
1402 ```
1403
1404 ```bash macOS theme={null}
1405 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1406 ```
1407
1408 ```powershell Windows theme={null}
1409 code $env:AppData\Claude\claude_desktop_config.json
1410 ```
1411 </CodeGroup>
1412
1413 You'll then add your servers in the `mcpServers` key.
1414 The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1415
1416 In this case, we'll add our single weather server like so:
1417
1418 <CodeGroup>
1419 ```json macOS/Linux theme={null}
1420 {
1421 "mcpServers": {
1422 "weather": {
1423 "command": "java",
1424 "args": [
1425 "-jar",
1426 "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar"
1427 ]
1428 }
1429 }
1430 }
1431 ```
1432
1433 ```json Windows theme={null}
1434 {
1435 "mcpServers": {
1436 "weather": {
1437 "command": "java",
1438 "args": [
1439 "-jar",
1440 "C:\\PATH\\TO\\PARENT\\FOLDER\\weather\\build\\libs\\weather-0.1.0-all.jar"
1441 ]
1442 }
1443 }
1444 }
1445 ```
1446 </CodeGroup>
1447
1448 This tells Claude for Desktop:
1449
1450 1. There's an MCP server named "weather"
1451 2. Launch it by running `java -jar /ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/build/libs/weather-0.1.0-all.jar`
1452
1453 Save the file, and restart **Claude for Desktop**.
1454 </Tab>
1455
1456 <Tab title="C#">
1457 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/csharp-sdk/tree/main/samples/QuickstartWeatherServer)
1458
1459 ### Prerequisite knowledge
1460
1461 This quickstart assumes you have familiarity with:
1462
1463 * C#
1464 * LLMs like Claude
1465 * .NET 8 or higher
1466
1467 ### Logging in MCP Servers
1468
1469 When implementing MCP servers, be careful about how you handle logging:
1470
1471 **For STDIO-based servers:** Never use `Console.WriteLine()` or `Console.Write()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
1472
1473 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1474
1475 ### Best Practices
1476
1477 * Use a logging library that writes to stderr or files.
1478
1479 ### System requirements
1480
1481 * [.NET 8 SDK](https://dotnet.microsoft.com/download/dotnet/8.0) or higher installed.
1482
1483 ### Set up your environment
1484
1485 First, let's install `dotnet` if you haven't already. You can download `dotnet` from [official Microsoft .NET website](https://dotnet.microsoft.com/download/). Verify your `dotnet` installation:
1486
1487 ```bash theme={null}
1488 dotnet --version
1489 ```
1490
1491 Now, let's create and set up your project:
1492
1493 <CodeGroup>
1494 ```bash macOS/Linux theme={null}
1495 # Create a new directory for our project
1496 mkdir weather
1497 cd weather
1498 # Initialize a new C# project
1499 dotnet new console
1500 ```
1501
1502 ```powershell Windows theme={null}
1503 # Create a new directory for our project
1504 mkdir weather
1505 cd weather
1506 # Initialize a new C# project
1507 dotnet new console
1508 ```
1509 </CodeGroup>
1510
1511 After running `dotnet new console`, you will be presented with a new C# project.
1512 You can open the project in your favorite IDE, such as [Visual Studio](https://visualstudio.microsoft.com/) or [Rider](https://www.jetbrains.com/rider/).
1513 Alternatively, you can create a C# application using the [Visual Studio project wizard](https://learn.microsoft.com/en-us/visualstudio/get-started/csharp/tutorial-console?view=vs-2022).
1514 After creating the project, add NuGet package for the Model Context Protocol SDK and hosting:
1515
1516 ```bash theme={null}
1517 # Add the Model Context Protocol SDK NuGet package
1518 dotnet add package ModelContextProtocol --prerelease
1519 # Add the .NET Hosting NuGet package
1520 dotnet add package Microsoft.Extensions.Hosting
1521 ```
1522
1523 Now let’s dive into building your server.
1524
1525 ## Building your server
1526
1527 Open the `Program.cs` file in your project and replace its contents with the following code:
1528
1529 ```csharp theme={null}
1530 using Microsoft.Extensions.DependencyInjection;
1531 using Microsoft.Extensions.Hosting;
1532 using ModelContextProtocol;
1533 using System.Net.Http.Headers;
1534
1535 var builder = Host.CreateEmptyApplicationBuilder(settings: null);
1536
1537 builder.Services.AddMcpServer()
1538 .WithStdioServerTransport()
1539 .WithToolsFromAssembly();
1540
1541 builder.Services.AddSingleton(_ =>
1542 {
1543 var client = new HttpClient() { BaseAddress = new Uri("https://api.weather.gov") };
1544 client.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("weather-tool", "1.0"));
1545 return client;
1546 });
1547
1548 var app = builder.Build();
1549
1550 await app.RunAsync();
1551 ```
1552
1553 <Note>
1554 When creating the `ApplicationHostBuilder`, ensure you use `CreateEmptyApplicationBuilder` instead of `CreateDefaultBuilder`. This ensures that the server does not write any additional messages to the console. This is only necessary for servers using STDIO transport.
1555 </Note>
1556
1557 This code sets up a basic console application that uses the Model Context Protocol SDK to create an MCP server with standard I/O transport.
1558
1559 ### Weather API helper functions
1560
1561 Create an extension class for `HttpClient` which helps simplify JSON request handling:
1562
1563 ```csharp theme={null}
1564 using System.Text.Json;
1565
1566 internal static class HttpClientExt
1567 {
1568 public static async Task<JsonDocument> ReadJsonDocumentAsync(this HttpClient client, string requestUri)
1569 {
1570 using var response = await client.GetAsync(requestUri);
1571 response.EnsureSuccessStatusCode();
1572 return await JsonDocument.ParseAsync(await response.Content.ReadAsStreamAsync());
1573 }
2786 }
2787}
2788```
2789
2790```json Windows theme={null}
2791{
2792 "mcpServers": {
2793 "weather": {
2794 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\weather.exe"
15742795 }
1575 ```
1576
1577 Next, define a class with the tool execution handlers for querying and converting responses from the National Weather Service API:
1578
1579 ```csharp theme={null}
1580 using ModelContextProtocol.Server;
1581 using System.ComponentModel;
1582 using System.Globalization;
1583 using System.Text.Json;
1584
1585 namespace QuickstartWeatherServer.Tools;
1586
1587 [McpServerToolType]
1588 public static class WeatherTools
1589 {
1590 [McpServerTool, Description("Get weather alerts for a US state code.")]
1591 public static async Task<string> GetAlerts(
1592 HttpClient client,
1593 [Description("The US state code to get alerts for.")] string state)
1594 {
1595 using var jsonDocument = await client.ReadJsonDocumentAsync($"/alerts/active/area/{state}");
1596 var jsonElement = jsonDocument.RootElement;
1597 var alerts = jsonElement.GetProperty("features").EnumerateArray();
1598
1599 if (!alerts.Any())
1600 {
1601 return "No active alerts for this state.";
1602 }
1603
1604 return string.Join("\n--\n", alerts.Select(alert =>
1605 {
1606 JsonElement properties = alert.GetProperty("properties");
1607 return $"""
1608 Event: {properties.GetProperty("event").GetString()}
1609 Area: {properties.GetProperty("areaDesc").GetString()}
1610 Severity: {properties.GetProperty("severity").GetString()}
1611 Description: {properties.GetProperty("description").GetString()}
1612 Instruction: {properties.GetProperty("instruction").GetString()}
1613 """;
1614 }));
1615 }
1616
1617 [McpServerTool, Description("Get weather forecast for a location.")]
1618 public static async Task<string> GetForecast(
1619 HttpClient client,
1620 [Description("Latitude of the location.")] double latitude,
1621 [Description("Longitude of the location.")] double longitude)
1622 {
1623 var pointUrl = string.Create(CultureInfo.InvariantCulture, $"/points/{latitude},{longitude}");
1624 using var jsonDocument = await client.ReadJsonDocumentAsync(pointUrl);
1625 var forecastUrl = jsonDocument.RootElement.GetProperty("properties").GetProperty("forecast").GetString()
1626 ?? throw new Exception($"No forecast URL provided by {client.BaseAddress}points/{latitude},{longitude}");
1627
1628 using var forecastDocument = await client.ReadJsonDocumentAsync(forecastUrl);
1629 var periods = forecastDocument.RootElement.GetProperty("properties").GetProperty("periods").EnumerateArray();
1630
1631 return string.Join("\n---\n", periods.Select(period => $"""
1632 {period.GetProperty("name").GetString()}
1633 Temperature: {period.GetProperty("temperature").GetInt32()}°F
1634 Wind: {period.GetProperty("windSpeed").GetString()} {period.GetProperty("windDirection").GetString()}
1635 Forecast: {period.GetProperty("detailedForecast").GetString()}
1636 """));
1637 }
1638 }
1639 ```
1640
1641 ### Running the server
1642
1643 Finally, run the server using the following command:
1644
1645 ```bash theme={null}
1646 dotnet run
1647 ```
1648
1649 This will start the server and listen for incoming requests on standard input/output.
1650
1651 ## Testing your server with Claude for Desktop
1652
1653 First, make sure you have Claude for Desktop installed. [You can install the latest version
1654 here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1655 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1656 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1657
1658 <CodeGroup>
1659 ```bash Linux theme={null}
1660 code ~/.config/Claude/claude_desktop_config.json
1661 ```
1662
1663 ```bash macOS theme={null}
1664 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1665 ```
1666
1667 ```powershell Windows theme={null}
1668 code $env:AppData\Claude\claude_desktop_config.json
1669 ```
1670 </CodeGroup>
1671
1672 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1673 In this case, we'll add our single weather server like so:
1674
1675 <CodeGroup>
1676 ```json macOS/Linux theme={null}
1677 {
1678 "mcpServers": {
1679 "weather": {
1680 "command": "dotnet",
1681 "args": ["run", "--project", "/ABSOLUTE/PATH/TO/PROJECT", "--no-build"]
1682 }
1683 }
1684 }
1685 ```
1686
1687 ```json Windows theme={null}
1688 {
1689 "mcpServers": {
1690 "weather": {
1691 "command": "dotnet",
1692 "args": [
1693 "run",
1694 "--project",
1695 "C:\\ABSOLUTE\\PATH\\TO\\PROJECT",
1696 "--no-build"
1697 ]
1698 }
1699 }
1700 }
1701 ```
1702 </CodeGroup>
1703
1704 This tells Claude for Desktop:
1705
1706 1. There's an MCP server named "weather"
1707 2. Launch it by running `dotnet run /ABSOLUTE/PATH/TO/PROJECT`
1708 Save the file, and restart **Claude for Desktop**.
1709 </Tab>
1710
1711 <Tab title="Ruby">
1712 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-ruby)
1713
1714 ### Prerequisite knowledge
1715
1716 This quickstart assumes you have familiarity with:
1717
1718 * Ruby
1719 * LLMs like Claude
1720
1721 ### Logging in MCP Servers
1722
1723 When implementing MCP servers, be careful about how you handle logging:
1724
1725 **For STDIO-based servers:** Never use `puts` or `print`, as they write to standard output (stdout) by default. Writing to stdout will corrupt the JSON-RPC messages and break your server.
1726
1727 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
1728
1729 ### Best Practices
1730
1731 * Use a logging library that writes to stderr or files.
1732
1733 ### Quick Examples
1734
1735 ```ruby theme={null}
1736 # ❌ Bad (STDIO)
1737 puts "Processing request"
1738
1739 # ✅ Good (STDIO)
1740 require "logger"
1741 logger = Logger.new($stderr)
1742 logger.info("Processing request")
1743 ```
1744
1745 ### System requirements
1746
1747 * Ruby 2.7 or higher installed.
1748
1749 ### Set up your environment
1750
1751 First, let's make sure you have Ruby installed. You can check by running:
1752
1753 ```bash theme={null}
1754 ruby --version
1755 ```
1756
1757 Now, let's create and set up our project:
1758
1759 <CodeGroup>
1760 ```bash macOS/Linux theme={null}
1761 # Create a new directory for our project
1762 mkdir weather
1763 cd weather
1764
1765 # Create a Gemfile
1766 bundle init
1767
1768 # Add the MCP SDK dependency
1769 bundle add mcp
1770
1771 # Create our server file
1772 touch weather.rb
1773 ```
1774
1775 ```powershell Windows theme={null}
1776 # Create a new directory for our project
1777 mkdir weather
1778 cd weather
1779
1780 # Create a Gemfile
1781 bundle init
1782
1783 # Add the MCP SDK dependency
1784 bundle add mcp
1785
1786 # Create our server file
1787 new-item weather.rb
1788 ```
1789 </CodeGroup>
1790
1791 Now let's dive into building your server.
1792
1793 ## Building your server
1794
1795 ### Importing packages and setting up constants
1796
1797 Open `weather.rb` and add these requires and constants at the top:
1798
1799 ```ruby theme={null}
1800 require "json"
1801 require "mcp"
1802 require "net/http"
1803 require "uri"
1804
1805 NWS_API_BASE = "https://api.weather.gov"
1806 USER_AGENT = "weather-app/1.0"
1807 ```
1808
1809 The `mcp` gem provides the Model Context Protocol SDK for Ruby, with classes for server implementation and stdio transport.
1810
1811 ### Helper methods
1812
1813 Next, let's add helper methods for querying and formatting data from the National Weather Service API:
1814
1815 ```ruby theme={null}
1816 module HelperMethods
1817 def make_nws_request(url)
1818 uri = URI(url)
1819 request = Net::HTTP::Get.new(uri)
1820 request["User-Agent"] = USER_AGENT
1821 request["Accept"] = "application/geo+json"
1822
1823 response = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
1824 http.request(request)
1825 end
1826
1827 raise "HTTP #{response.code}: #{response.message}" unless response.is_a?(Net::HTTPSuccess)
1828
1829 JSON.parse(response.body)
1830 end
1831
1832 def format_alert(feature)
1833 properties = feature["properties"]
1834
1835 <<~ALERT
1836 Event: #{properties["event"] || "Unknown"}
1837 Area: #{properties["areaDesc"] || "Unknown"}
1838 Severity: #{properties["severity"] || "Unknown"}
1839 Description: #{properties["description"] || "No description available"}
1840 Instructions: #{properties["instruction"] || "No specific instructions provided"}
1841 ALERT
1842 end
1843 end
1844 ```
1845
1846 ### Implementing tool execution
1847
1848 Now let's define our tool classes. Each tool subclasses `MCP::Tool` and implements the tool logic:
1849
1850 ```ruby theme={null}
1851 class GetAlerts < MCP::Tool
1852 extend HelperMethods
1853
1854 tool_name "get_alerts"
1855 description "Get weather alerts for a US state"
1856 input_schema(
1857 properties: {
1858 state: {
1859 type: "string",
1860 description: "Two-letter US state code (e.g. CA, NY)"
1861 }
1862 },
1863 required: ["state"]
1864 )
1865
1866 def self.call(state:)
1867 url = "#{NWS_API_BASE}/alerts/active/area/#{state.upcase}"
1868 data = make_nws_request(url)
1869
1870 if data["features"].empty?
1871 return MCP::Tool::Response.new([{
1872 type: "text",
1873 text: "No active alerts for this state."
1874 }])
1875 end
1876
1877 alerts = data["features"].map { |feature| format_alert(feature) }
1878 MCP::Tool::Response.new([{
1879 type: "text",
1880 text: alerts.join("\n---\n")
1881 }])
1882 end
1883 end
1884
1885 class GetForecast < MCP::Tool
1886 extend HelperMethods
1887
1888 tool_name "get_forecast"
1889 description "Get weather forecast for a location"
1890 input_schema(
1891 properties: {
1892 latitude: {
1893 type: "number",
1894 description: "Latitude of the location"
1895 },
1896 longitude: {
1897 type: "number",
1898 description: "Longitude of the location"
1899 }
1900 },
1901 required: ["latitude", "longitude"]
1902 )
1903
1904 def self.call(latitude:, longitude:)
1905 # First get the forecast grid endpoint.
1906 points_url = "#{NWS_API_BASE}/points/#{latitude},#{longitude}"
1907 points_data = make_nws_request(points_url)
1908
1909 # Get the forecast URL from the points response.
1910 forecast_url = points_data["properties"]["forecast"]
1911 forecast_data = make_nws_request(forecast_url)
1912
1913 # Format the periods into a readable forecast.
1914 periods = forecast_data["properties"]["periods"]
1915 forecasts = periods.first(5).map do |period|
1916 <<~FORECAST
1917 #{period["name"]}:
1918 Temperature: #{period["temperature"]}°#{period["temperatureUnit"]}
1919 Wind: #{period["windSpeed"]} #{period["windDirection"]}
1920 Forecast: #{period["detailedForecast"]}
1921 FORECAST
1922 end
1923
1924 MCP::Tool::Response.new([{
1925 type: "text",
1926 text: forecasts.join("\n---\n")
1927 }])
1928 end
1929 end
1930 ```
1931
1932 ### Running the server
1933
1934 Finally, initialize and run the server:
1935
1936 ```ruby theme={null}
1937 server = MCP::Server.new(
1938 name: "weather",
1939 version: "1.0.0",
1940 tools: [GetAlerts, GetForecast]
1941 )
1942
1943 transport = MCP::Server::Transports::StdioTransport.new(server)
1944 transport.open
1945 ```
1946
1947 Your server is complete! Run `bundle exec ruby weather.rb` to start the MCP server, which will listen for messages from MCP hosts.
1948
1949 Let's now test your server from an existing MCP host, Claude for Desktop.
1950
1951 ## Testing your server with Claude for Desktop
1952
1953 First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
1954
1955 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
1956
1957 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
1958
1959 <CodeGroup>
1960 ```bash Linux theme={null}
1961 code ~/.config/Claude/claude_desktop_config.json
1962 ```
1963
1964 ```bash macOS theme={null}
1965 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
1966 ```
1967
1968 ```powershell Windows theme={null}
1969 code $env:AppData\Claude\claude_desktop_config.json
1970 ```
1971 </CodeGroup>
1972
1973 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
1974
1975 In this case, we'll add our single weather server like so:
1976
1977 <CodeGroup>
1978 ```json macOS/Linux theme={null}
1979 {
1980 "mcpServers": {
1981 "weather": {
1982 "command": "bundle",
1983 "args": ["exec", "ruby", "weather.rb"],
1984 "cwd": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather"
1985 }
1986 }
1987 }
1988 ```
1989
1990 ```json Windows theme={null}
1991 {
1992 "mcpServers": {
1993 "weather": {
1994 "command": "bundle",
1995 "args": ["exec", "ruby", "weather.rb"],
1996 "cwd": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather"
1997 }
1998 }
1999 }
2000 ```
2001 </CodeGroup>
2002
2003 <Note>
2004 Make sure you pass in the absolute path to your project directory in the `cwd` field. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path.
2005 </Note>
2006
2007 This tells Claude for Desktop:
2008
2009 1. There's an MCP server named "weather"
2010 2. Launch it by running `bundle exec ruby weather.rb` in the specified directory
2011
2012 Save the file, and restart **Claude for Desktop**.
2013 </Tab>
2014
2015 <Tab title="Rust">
2016 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-rust)
2017
2018 ### Prerequisite knowledge
2019
2020 This quickstart assumes you have familiarity with:
2021
2022 * Rust programming language
2023 * Async/await in Rust
2024 * LLMs like Claude
2025
2026 ### Logging in MCP Servers
2027
2028 When implementing MCP servers, be careful about how you handle logging:
2029
2030 **For STDIO-based servers:** Never use `println!()` or `print!()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
2031
2032 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
2033
2034 ### Best Practices
2035
2036 * Use a logging library that writes to stderr or files, such as `tracing` or `log` in Rust.
2037 * Configure your logging framework to avoid stdout output.
2038
2039 ### Quick Examples
2040
2041 ```rust theme={null}
2042 // ❌ Bad (STDIO)
2043 println!("Processing request");
2044
2045 // ✅ Good (STDIO)
2046 eprintln!("Processing request"); // writes to stderr
2047 ```
2048
2049 ### System requirements
2050
2051 * Rust 1.70 or higher installed.
2052 * Cargo (comes with Rust installation).
2053
2054 ### Set up your environment
2055
2056 First, let's install Rust if you haven't already. You can install Rust from [rust-lang.org](https://www.rust-lang.org/tools/install):
2057
2058 <CodeGroup>
2059 ```bash macOS/Linux theme={null}
2060 curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
2061 ```
2062
2063 ```powershell Windows theme={null}
2064 # Download and run rustup-init.exe from https://rustup.rs/
2065 ```
2066 </CodeGroup>
2067
2068 Verify your Rust installation:
2069
2070 ```bash theme={null}
2071 rustc --version
2072 cargo --version
2073 ```
2074
2075 Now, let's create and set up our project:
2076
2077 <CodeGroup>
2078 ```bash macOS/Linux theme={null}
2079 # Create a new Rust project
2080 cargo new weather
2081 cd weather
2082 ```
2083
2084 ```powershell Windows theme={null}
2085 # Create a new Rust project
2086 cargo new weather
2087 cd weather
2088 ```
2089 </CodeGroup>
2090
2091 Update your `Cargo.toml` to add the required dependencies:
2092
2093 ```toml Cargo.toml theme={null}
2094 [package]
2095 name = "weather"
2096 version = "0.1.0"
2097 edition = "2024"
2098
2099 [dependencies]
2100 rmcp = { version = "0.3", features = ["server", "macros", "transport-io"] }
2101 tokio = { version = "1.46", features = ["full"] }
2102 reqwest = { version = "0.12", features = ["json"] }
2103 serde = { version = "1.0", features = ["derive"] }
2104 serde_json = "1.0"
2105 anyhow = "1.0"
2106 tracing = "0.1"
2107 tracing-subscriber = { version = "0.3", features = ["env-filter", "std", "fmt"] }
2108 ```
2109
2110 Now let's dive into building your server.
2111
2112 ## Building your server
2113
2114 ### Importing packages and constants
2115
2116 Open `src/main.rs` and add these imports and constants at the top:
2117
2118 ```rust theme={null}
2119 use anyhow::Result;
2120 use rmcp::{
2121 ServerHandler, ServiceExt,
2122 handler::server::{router::tool::ToolRouter, tool::Parameters},
2123 model::*,
2124 schemars, tool, tool_handler, tool_router,
2125 };
2126 use serde::Deserialize;
2127 use serde::de::DeserializeOwned;
2128
2129 const NWS_API_BASE: &str = "https://api.weather.gov";
2130 const USER_AGENT: &str = "weather-app/1.0";
2131 ```
2132
2133 The `rmcp` crate provides the Model Context Protocol SDK for Rust, with features for server implementation, procedural macros, and stdio transport.
2134
2135 ### Data structures
2136
2137 Next, let's define the data structures for deserializing responses from the National Weather Service API:
2138
2139 ```rust theme={null}
2140 #[derive(Debug, Deserialize)]
2141 struct AlertsResponse {
2142 features: Vec<AlertFeature>,
2143 }
2144
2145 #[derive(Debug, Deserialize)]
2146 struct AlertFeature {
2147 properties: AlertProperties,
2148 }
2149
2150 #[derive(Debug, Deserialize)]
2151 struct AlertProperties {
2152 event: Option<String>,
2153 #[serde(rename = "areaDesc")]
2154 area_desc: Option<String>,
2155 severity: Option<String>,
2156 description: Option<String>,
2157 instruction: Option<String>,
2158 }
2159
2160 #[derive(Debug, Deserialize)]
2161 struct PointsResponse {
2162 properties: PointsProperties,
2163 }
2164
2165 #[derive(Debug, Deserialize)]
2166 struct PointsProperties {
2167 forecast: String,
2168 }
2169
2170 #[derive(Debug, Deserialize)]
2171 struct ForecastResponse {
2172 properties: ForecastProperties,
2173 }
2174
2175 #[derive(Debug, Deserialize)]
2176 struct ForecastProperties {
2177 periods: Vec<ForecastPeriod>,
2178 }
2179
2180 #[derive(Debug, Deserialize)]
2181 struct ForecastPeriod {
2182 name: String,
2183 temperature: i32,
2184 #[serde(rename = "temperatureUnit")]
2185 temperature_unit: String,
2186 #[serde(rename = "windSpeed")]
2187 wind_speed: String,
2188 #[serde(rename = "windDirection")]
2189 wind_direction: String,
2190 #[serde(rename = "detailedForecast")]
2191 detailed_forecast: String,
2192 }
2193 ```
2194
2195 Now define the request types that MCP clients will send:
2196
2197 ```rust theme={null}
2198 #[derive(serde::Deserialize, schemars::JsonSchema)]
2199 pub struct MCPForecastRequest {
2200 latitude: f32,
2201 longitude: f32,
2202 }
2203
2204 #[derive(serde::Deserialize, schemars::JsonSchema)]
2205 pub struct MCPAlertRequest {
2206 state: String,
2207 }
2208 ```
2209
2210 ### Helper functions
2211
2212 Add helper functions for making API requests and formatting responses:
2213
2214 ```rust theme={null}
2215 async fn make_nws_request<T: DeserializeOwned>(url: &str) -> Result<T> {
2216 let client = reqwest::Client::new();
2217 let rsp = client
2218 .get(url)
2219 .header(reqwest::header::USER_AGENT, USER_AGENT)
2220 .header(reqwest::header::ACCEPT, "application/geo+json")
2221 .send()
2222 .await?
2223 .error_for_status()?;
2224 Ok(rsp.json::<T>().await?)
2225 }
2226
2227 fn format_alert(feature: &AlertFeature) -> String {
2228 let props = &feature.properties;
2229 format!(
2230 "Event: {}\nArea: {}\nSeverity: {}\nDescription: {}\nInstructions: {}",
2231 props.event.as_deref().unwrap_or("Unknown"),
2232 props.area_desc.as_deref().unwrap_or("Unknown"),
2233 props.severity.as_deref().unwrap_or("Unknown"),
2234 props
2235 .description
2236 .as_deref()
2237 .unwrap_or("No description available"),
2238 props
2239 .instruction
2240 .as_deref()
2241 .unwrap_or("No specific instructions provided")
2242 )
2243 }
2244
2245 fn format_period(period: &ForecastPeriod) -> String {
2246 format!(
2247 "{}:\nTemperature: {}°{}\nWind: {} {}\nForecast: {}",
2248 period.name,
2249 period.temperature,
2250 period.temperature_unit,
2251 period.wind_speed,
2252 period.wind_direction,
2253 period.detailed_forecast
2254 )
2255 }
2256 ```
2257
2258 ### Implementing the Weather server and tools
2259
2260 Now let's implement the main Weather server struct with the tool handlers:
2261
2262 ```rust theme={null}
2263 pub struct Weather {
2264 tool_router: ToolRouter<Weather>,
2265 }
2266
2267 #[tool_router]
2268 impl Weather {
2269 fn new() -> Self {
2270 Self {
2271 tool_router: Self::tool_router(),
2272 }
2273 }
2274
2275 #[tool(description = "Get weather alerts for a US state.")]
2276 async fn get_alerts(
2277 &self,
2278 Parameters(MCPAlertRequest { state }): Parameters<MCPAlertRequest>,
2279 ) -> String {
2280 let url = format!(
2281 "{}/alerts/active/area/{}",
2282 NWS_API_BASE,
2283 state.to_uppercase()
2284 );
2285
2286 match make_nws_request::<AlertsResponse>(&url).await {
2287 Ok(data) => {
2288 if data.features.is_empty() {
2289 "No active alerts for this state.".to_string()
2290 } else {
2291 data.features
2292 .iter()
2293 .map(format_alert)
2294 .collect::<Vec<_>>()
2295 .join("\n---\n")
2296 }
2297 }
2298 Err(_) => "Unable to fetch alerts or no alerts found.".to_string(),
2299 }
2300 }
2301
2302 #[tool(description = "Get weather forecast for a location.")]
2303 async fn get_forecast(
2304 &self,
2305 Parameters(MCPForecastRequest {
2306 latitude,
2307 longitude,
2308 }): Parameters<MCPForecastRequest>,
2309 ) -> String {
2310 let points_url = format!("{NWS_API_BASE}/points/{latitude},{longitude}");
2311 let Ok(points_data) = make_nws_request::<PointsResponse>(&points_url).await else {
2312 return "Unable to fetch forecast data for this location.".to_string();
2313 };
2314
2315 let forecast_url = points_data.properties.forecast;
2316
2317 let Ok(forecast_data) = make_nws_request::<ForecastResponse>(&forecast_url).await else {
2318 return "Unable to fetch forecast data for this location.".to_string();
2319 };
2320
2321 let periods = &forecast_data.properties.periods;
2322 let forecast_summary: String = periods
2323 .iter()
2324 .take(5) // Next 5 periods only
2325 .map(format_period)
2326 .collect::<Vec<String>>()
2327 .join("\n---\n");
2328 forecast_summary
2329 }
2330 }
2331 ```
2332
2333 The `#[tool_router]` macro automatically generates the routing logic, and the `#[tool]` attribute marks methods as MCP tools.
2334
2335 ### Implementing the ServerHandler
2336
2337 Implement the `ServerHandler` trait to define server capabilities:
2338
2339 ```rust theme={null}
2340 #[tool_handler]
2341 impl ServerHandler for Weather {
2342 fn get_info(&self) -> ServerInfo {
2343 ServerInfo {
2344 capabilities: ServerCapabilities::builder().enable_tools().build(),
2345 ..Default::default()
2346 }
2347 }
2348 }
2349 ```
2350
2351 ### Running the server
2352
2353 Finally, implement the main function to run the server with stdio transport:
2354
2355 ```rust theme={null}
2356 #[tokio::main]
2357 async fn main() -> Result<()> {
2358 let transport = (tokio::io::stdin(), tokio::io::stdout());
2359 let service = Weather::new().serve(transport).await?;
2360 service.waiting().await?;
2361 Ok(())
2362 }
2363 ```
2364
2365 Build your server with:
2366
2367 ```bash theme={null}
2368 cargo build --release
2369 ```
2370
2371 The compiled binary will be in `target/release/weather`.
2372
2373 Let's now test your server from an existing MCP host, Claude for Desktop.
2374
2375 ## Testing your server with Claude for Desktop
2376
2377 First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2378
2379 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2380
2381 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2382
2383 <CodeGroup>
2384 ```bash Linux theme={null}
2385 code ~/.config/Claude/claude_desktop_config.json
2386 ```
2387
2388 ```bash macOS theme={null}
2389 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2390 ```
2391
2392 ```powershell Windows theme={null}
2393 code $env:AppData\Claude\claude_desktop_config.json
2394 ```
2395 </CodeGroup>
2396
2397 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2398
2399 In this case, we'll add our single weather server like so:
2400
2401 <CodeGroup>
2402 ```json macOS/Linux theme={null}
2403 {
2404 "mcpServers": {
2405 "weather": {
2406 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/target/release/weather"
2407 }
2408 }
2409 }
2410 ```
2411
2412 ```json Windows theme={null}
2413 {
2414 "mcpServers": {
2415 "weather": {
2416 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\target\\release\\weather.exe"
2417 }
2418 }
2419 }
2420 ```
2421 </CodeGroup>
2422
2423 <Note>
2424 Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2425 </Note>
2426
2427 This tells Claude for Desktop:
2428
2429 1. There's an MCP server named "weather"
2430 2. Launch it by running the compiled binary at the specified path
2431
2432 Save the file, and restart **Claude for Desktop**.
2433 </Tab>
2434
2435 <Tab title="Go">
2436 Let's get started with building our weather server! [You can find the complete code for what we'll be building here.](https://github.com/modelcontextprotocol/quickstart-resources/tree/main/weather-server-go)
2437
2438 ### Prerequisite knowledge
2439
2440 This quickstart assumes you have familiarity with:
2441
2442 * Go
2443 * LLMs like Claude
2444
2445 ### Logging in MCP Servers
2446
2447 When implementing MCP servers, be careful about how you handle logging:
2448
2449 **For STDIO-based servers:** Never use `fmt.Println()` or `fmt.Printf()`, as they write to standard output (stdout). Writing to stdout will corrupt the JSON-RPC messages and break your server.
2450
2451 **For HTTP-based servers:** Standard output logging is fine since it doesn't interfere with HTTP responses.
2452
2453 ### Best Practices
2454
2455 * Use `log.Println()` (which defaults to stderr) or a logging library that writes to stderr or files.
2456 * Use `fmt.Fprintf(os.Stderr, ...)` to write to stderr explicitly.
2457
2458 ### Quick Examples
2459
2460 ```go theme={null}
2461 // ❌ Bad (STDIO)
2462 fmt.Println("Processing request")
2463
2464 // ✅ Good (STDIO)
2465 log.Println("Processing request") // defaults to stderr
2466
2467 // ✅ Good (STDIO)
2468 fmt.Fprintln(os.Stderr, "Processing request")
2469 ```
2470
2471 ### System requirements
2472
2473 * Go 1.24 or higher installed.
2474
2475 ### Set up your environment
2476
2477 First, let's install Go if you haven't already. You can download and install Go from [go.dev](https://go.dev/dl/).
2478
2479 Verify your Go installation:
2480
2481 ```bash theme={null}
2482 go version
2483 ```
2484
2485 Now, let's create and set up our project:
2486
2487 <CodeGroup>
2488 ```bash macOS/Linux theme={null}
2489 # Create a new directory for our project
2490 mkdir weather
2491 cd weather
2492
2493 # Initialize Go module
2494 go mod init weather
2495
2496 # Install dependencies
2497 go get github.com/modelcontextprotocol/go-sdk/mcp
2498
2499 # Create our server file
2500 touch main.go
2501 ```
2502
2503 ```powershell Windows theme={null}
2504 # Create a new directory for our project
2505 md weather
2506 cd weather
2507
2508 # Initialize Go module
2509 go mod init weather
2510
2511 # Install dependencies
2512 go get github.com/modelcontextprotocol/go-sdk/mcp
2513
2514 # Create our server file
2515 new-item main.go
2516 ```
2517 </CodeGroup>
2518
2519 Now let's dive into building your server.
2520
2521 ## Building your server
2522
2523 ### Importing packages and constants
2524
2525 Add these to the top of your `main.go`:
2526
2527 ```go theme={null}
2528 package main
2529
2530 import (
2531 "cmp"
2532 "context"
2533 "encoding/json"
2534 "fmt"
2535 "io"
2536 "log"
2537 "net/http"
2538 "strings"
2539
2540 "github.com/modelcontextprotocol/go-sdk/mcp"
2541 )
2542
2543 const (
2544 NWSAPIBase = "https://api.weather.gov"
2545 UserAgent = "weather-app/1.0"
2546 )
2547 ```
2548
2549 ### Data structures
2550
2551 Next, let's define the data structures used by our tools:
2552
2553 ```go theme={null}
2554 type PointsResponse struct {
2555 Properties struct {
2556 Forecast string `json:"forecast"`
2557 } `json:"properties"`
2558 }
2559
2560 type ForecastResponse struct {
2561 Properties struct {
2562 Periods []ForecastPeriod `json:"periods"`
2563 } `json:"properties"`
2564 }
2565
2566 type ForecastPeriod struct {
2567 Name string `json:"name"`
2568 Temperature int `json:"temperature"`
2569 TemperatureUnit string `json:"temperatureUnit"`
2570 WindSpeed string `json:"windSpeed"`
2571 WindDirection string `json:"windDirection"`
2572 DetailedForecast string `json:"detailedForecast"`
2573 }
2574
2575 type AlertsResponse struct {
2576 Features []AlertFeature `json:"features"`
2577 }
2578
2579 type AlertFeature struct {
2580 Properties AlertProperties `json:"properties"`
2581 }
2582
2583 type AlertProperties struct {
2584 Event string `json:"event"`
2585 AreaDesc string `json:"areaDesc"`
2586 Severity string `json:"severity"`
2587 Description string `json:"description"`
2588 Instruction string `json:"instruction"`
2589 }
2590
2591 type ForecastInput struct {
2592 Latitude float64 `json:"latitude" jsonschema:"Latitude of the location"`
2593 Longitude float64 `json:"longitude" jsonschema:"Longitude of the location"`
2594 }
2595
2596 type AlertsInput struct {
2597 State string `json:"state" jsonschema:"Two-letter US state code (e.g. CA, NY)"`
2598 }
2599 ```
2600
2601 ### Helper functions
2602
2603 Next, let's add our helper functions for querying and formatting the data from the National Weather Service API:
2604
2605 ```go theme={null}
2606 func makeNWSRequest[T any](ctx context.Context, url string) (*T, error) {
2607 req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
2608 if err != nil {
2609 return nil, fmt.Errorf("failed to create request: %w", err)
2610 }
2611
2612 req.Header.Set("User-Agent", UserAgent)
2613 req.Header.Set("Accept", "application/geo+json")
2614
2615 client := http.DefaultClient
2616 resp, err := client.Do(req)
2617 if err != nil {
2618 return nil, fmt.Errorf("failed to make request to %s: %w", url, err)
2619 }
2620 defer resp.Body.Close()
2621
2622 if resp.StatusCode != http.StatusOK {
2623 body, _ := io.ReadAll(resp.Body)
2624 return nil, fmt.Errorf("HTTP error %d: %s", resp.StatusCode, string(body))
2625 }
2626
2627 var result T
2628 if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
2629 return nil, fmt.Errorf("failed to decode response: %w", err)
2630 }
2631
2632 return &result, nil
2633 }
2634
2635 func formatAlert(alert AlertFeature) string {
2636 props := alert.Properties
2637 event := cmp.Or(props.Event, "Unknown")
2638 areaDesc := cmp.Or(props.AreaDesc, "Unknown")
2639 severity := cmp.Or(props.Severity, "Unknown")
2640 description := cmp.Or(props.Description, "No description available")
2641 instruction := cmp.Or(props.Instruction, "No specific instructions provided")
2642
2643 return fmt.Sprintf(`
2644 Event: %s
2645 Area: %s
2646 Severity: %s
2647 Description: %s
2648 Instructions: %s
2649 `, event, areaDesc, severity, description, instruction)
2650 }
2651
2652 func formatPeriod(period ForecastPeriod) string {
2653 return fmt.Sprintf(`
2654 %s:
2655 Temperature: %d°%s
2656 Wind: %s %s
2657 Forecast: %s
2658 `, period.Name, period.Temperature, period.TemperatureUnit,
2659 period.WindSpeed, period.WindDirection, period.DetailedForecast)
2660 }
2661 ```
2662
2663 ### Implementing tool execution
2664
2665 The tool execution handler is responsible for actually executing the logic of each tool. Let's add it:
2666
2667 ```go theme={null}
2668 func getForecast(ctx context.Context, req *mcp.CallToolRequest, input ForecastInput) (
2669 *mcp.CallToolResult, any, error,
2670 ) {
2671 // Get points data
2672 pointsURL := fmt.Sprintf("%s/points/%f,%f", NWSAPIBase, input.Latitude, input.Longitude)
2673 pointsData, err := makeNWSRequest[PointsResponse](ctx, pointsURL)
2674 if err != nil {
2675 return &mcp.CallToolResult{
2676 Content: []mcp.Content{
2677 &mcp.TextContent{Text: "Unable to fetch forecast data for this location."},
2678 },
2679 }, nil, nil
2680 }
2681
2682 // Get forecast data
2683 forecastURL := pointsData.Properties.Forecast
2684 if forecastURL == "" {
2685 return &mcp.CallToolResult{
2686 Content: []mcp.Content{
2687 &mcp.TextContent{Text: "Unable to fetch forecast URL."},
2688 },
2689 }, nil, nil
2690 }
2691
2692 forecastData, err := makeNWSRequest[ForecastResponse](ctx, forecastURL)
2693 if err != nil {
2694 return &mcp.CallToolResult{
2695 Content: []mcp.Content{
2696 &mcp.TextContent{Text: "Unable to fetch detailed forecast."},
2697 },
2698 }, nil, nil
2699 }
2700
2701 // Format the periods
2702 periods := forecastData.Properties.Periods
2703 if len(periods) == 0 {
2704 return &mcp.CallToolResult{
2705 Content: []mcp.Content{
2706 &mcp.TextContent{Text: "No forecast periods available."},
2707 },
2708 }, nil, nil
2709 }
2710
2711 // Show next 5 periods
2712 var forecasts []string
2713 for i := range min(5, len(periods)) {
2714 forecasts = append(forecasts, formatPeriod(periods[i]))
2715 }
2716
2717 result := strings.Join(forecasts, "\n---\n")
2718
2719 return &mcp.CallToolResult{
2720 Content: []mcp.Content{
2721 &mcp.TextContent{Text: result},
2722 },
2723 }, nil, nil
2724 }
2725
2726 func getAlerts(ctx context.Context, req *mcp.CallToolRequest, input AlertsInput) (
2727 *mcp.CallToolResult, any, error,
2728 ) {
2729 // Build alerts URL
2730 stateCode := strings.ToUpper(input.State)
2731 alertsURL := fmt.Sprintf("%s/alerts/active/area/%s", NWSAPIBase, stateCode)
2732
2733 alertsData, err := makeNWSRequest[AlertsResponse](ctx, alertsURL)
2734 if err != nil {
2735 return &mcp.CallToolResult{
2736 Content: []mcp.Content{
2737 &mcp.TextContent{Text: "Unable to fetch alerts or no alerts found."},
2738 },
2739 }, nil, nil
2740 }
2741
2742 // Check if there are any alerts
2743 if len(alertsData.Features) == 0 {
2744 return &mcp.CallToolResult{
2745 Content: []mcp.Content{
2746 &mcp.TextContent{Text: "No active alerts for this state."},
2747 },
2748 }, nil, nil
2749 }
2750
2751 // Format alerts
2752 var alerts []string
2753 for _, feature := range alertsData.Features {
2754 alerts = append(alerts, formatAlert(feature))
2755 }
2756
2757 result := strings.Join(alerts, "\n---\n")
2758
2759 return &mcp.CallToolResult{
2760 Content: []mcp.Content{
2761 &mcp.TextContent{Text: result},
2762 },
2763 }, nil, nil
2764 }
2765 ```
2766
2767 ### Running the server
2768
2769 Finally, implement the main function to run the server:
2770
2771 ```go theme={null}
2772 func main() {
2773 // Create MCP server
2774 server := mcp.NewServer(&mcp.Implementation{
2775 Name: "weather",
2776 Version: "1.0.0",
2777 }, nil)
2778
2779 // Add get_forecast tool
2780 mcp.AddTool(server, &mcp.Tool{
2781 Name: "get_forecast",
2782 Description: "Get weather forecast for a location",
2783 }, getForecast)
2784
2785 // Add get_alerts tool
2786 mcp.AddTool(server, &mcp.Tool{
2787 Name: "get_alerts",
2788 Description: "Get weather alerts for a US state",
2789 }, getAlerts)
2790
2791 // Run server on stdio transport
2792 if err := server.Run(context.Background(), &mcp.StdioTransport{}); err != nil {
2793 log.Fatal(err)
2794 }
2795 }
2796 ```
2797
2798 Build your server with:
2799
2800 ```bash theme={null}
2801 go build -o weather .
2802 ```
2803
2804 The compiled binary will be in `./weather`.
2805
2806 Let's now test your server from an existing MCP host, Claude for Desktop.
2807
2808 ## Testing your server with Claude for Desktop
2809
2810 First, make sure you have Claude for Desktop installed. [You can install the latest version here.](https://claude.ai/download) If you already have Claude for Desktop, **make sure it's updated to the latest version.**
2811
2812 We'll need to configure Claude for Desktop for whichever MCP servers you want to use. To do this, open your Claude for Desktop App configuration at `~/Library/Application Support/Claude/claude_desktop_config.json` in a text editor. Make sure to create the file if it doesn't exist.
2813
2814 For example, if you have [VS Code](https://code.visualstudio.com/) installed:
2815
2816 <CodeGroup>
2817 ```bash Linux theme={null}
2818 code ~/.config/Claude/claude_desktop_config.json
2819 ```
2820
2821 ```bash macOS theme={null}
2822 code ~/Library/Application\ Support/Claude/claude_desktop_config.json
2823 ```
2824
2825 ```powershell Windows theme={null}
2826 code $env:AppData\Claude\claude_desktop_config.json
2827 ```
2828 </CodeGroup>
2829
2830 You'll then add your servers in the `mcpServers` key. The MCP UI elements will only show up in Claude for Desktop if at least one server is properly configured.
2831
2832 In this case, we'll add our single weather server like so:
2833
2834 <CodeGroup>
2835 ```json macOS/Linux theme={null}
2836 {
2837 "mcpServers": {
2838 "weather": {
2839 "command": "/ABSOLUTE/PATH/TO/PARENT/FOLDER/weather/weather"
2840 }
2841 }
2842 }
2843 ```
2844
2845 ```json Windows theme={null}
2846 {
2847 "mcpServers": {
2848 "weather": {
2849 "command": "C:\\ABSOLUTE\\PATH\\TO\\PARENT\\FOLDER\\weather\\weather.exe"
2850 }
2851 }
2852 }
2853 ```
2854 </CodeGroup>
2855
2856 <Note>
2857 Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2858 </Note>
2859
2860 This tells Claude for Desktop:
2861
2862 1. There's an MCP server named "weather"
2863 2. Launch it by running the compiled binary at the specified path
2864
2865 Save the file, and restart **Claude for Desktop**.
2866 </Tab>
2867</Tabs>
2796 }
2797}
2798```
2799
2800> [!NOTE]
2801>
2802> Make sure you pass in the absolute path to your compiled binary. You can get this by running `pwd` on macOS/Linux or `cd` on Windows Command Prompt from your project directory. On Windows, remember to use double backslashes (`\\`) or forward slashes (`/`) in the JSON path, and add the `.exe` extension.
2803
2804This tells Claude for Desktop:
2805
28061. There's an MCP server named "weather"
28072. Launch it by running the compiled binary at the specified path
2808
2809Save the file, and restart **Claude for Desktop**.
28682810
28692811### Test with commands
28702812
2871Let's make sure Claude for Desktop is picking up the two tools we've exposed in our `weather` server. You can do this by looking for the "Add files, connectors, and more /" <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/claude-add-files-connectors-and-more.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=53acf21f6807dd5323b70b84b5d98d8a" style={{display: 'inline', margin: 0, height: '1.3em', width: 'auto'}} width="33" height="33" data-path="images/claude-add-files-connectors-and-more.png" /> icon:
2872
2873<Frame>
2874 <img src="https://mintcdn.com/mcp/zNouQwo2h8cbxlDS/images/visual-indicator-mcp-tools.png?fit=max&auto=format&n=zNouQwo2h8cbxlDS&q=85&s=1bf23a2cfc5f6dd3dac1c7574cceebc9" width="684" height="133" data-path="images/visual-indicator-mcp-tools.png" />
2875</Frame>
2813Let's make sure Claude for Desktop is picking up the two tools we've exposed in our `weather` server. You can do this by looking for the "Add files, connectors, and more /"  icon:
2814
2815
28762816
28772817After clicking on the plus icon, hover over the "Connectors" menu. You should see the `weather` servers listed:
28782818
2879<Frame>
2880 <img src="https://mintcdn.com/mcp/zNouQwo2h8cbxlDS/images/available-mcp-tools.png?fit=max&auto=format&n=zNouQwo2h8cbxlDS&q=85&s=e2ace1ac88895a5fe30ebd8d01456bc3" width="437" height="244" data-path="images/available-mcp-tools.png" />
2881</Frame>
2819
28822820
28832821If your server isn't being picked up by Claude for Desktop, proceed to the [Troubleshooting](#troubleshooting) section for debugging tips.
28842822
from line 2825
28872825* What's the weather in Sacramento?
28882826* What are the active weather alerts in Texas?
28892827
2890<Frame>
2891 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/current-weather.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=dce7b2f8a06c20ba358e4bd2e75fa4c7" width="2780" height="1849" data-path="images/current-weather.png" />
2892</Frame>
2893
2894<Frame>
2895 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/weather-alerts.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=c4762bf2bd84a8781846d2965af3e4a4" width="2809" height="1850" data-path="images/weather-alerts.png" />
2896</Frame>
2897
2898<Note>
2899 Since this is the US National Weather service, the queries will only work for US locations.
2900</Note>
2828
2829
2830
2831
2832> [!NOTE]
2833>
2834> Since this is the US National Weather service, the queries will only work for US locations.
29012835
29022836## What's happening under the hood
29032837
from line 2846
29122846
29132847## Troubleshooting
29142848
2915<AccordionGroup>
2916 <Accordion title="Claude for Desktop Integration Issues">
2917 **Getting logs from Claude for Desktop**
2918
2919 Claude.app logging related to MCP is written to log files in `~/Library/Logs/Claude` (macOS) or `~/.config/Claude/logs/` (Linux):
2920
2921 * `mcp.log` will contain general logging about MCP connections and connection failures.
2922 * Files named `mcp-server-SERVERNAME.log` will contain the stderr output from the named server. Stdio servers may use stderr for all their logging, so these files are not limited to errors.
2923
2924 You can run the following command to list recent logs and follow along with any new ones:
2925
2926 ```bash macOS theme={null}
2927 # Check Claude's logs for errors
2928 tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
2929 ```
2930
2931 ```bash Linux theme={null}
2932 # Check Claude's logs for errors
2933 tail -n 20 -f ~/.config/Claude/logs/mcp*.log
2934 ```
2935
2936 **Server not showing up in Claude**
2937
2938 1. Check your `claude_desktop_config.json` file syntax
2939 2. Make sure the path to your project is absolute and not relative
2940 3. Restart Claude for Desktop completely
2941
2942 <Warning>
2943 To properly restart Claude for Desktop, you must fully quit the application:
2944
2945 * **Windows**: Right-click the Claude icon in the system tray (which may be hidden in the "hidden icons" menu) and select "Quit" or "Exit".
2946 * **macOS**: Use Cmd+Q or select "Quit Claude" from the menu bar.
2947 * **Linux**: Right-click the Claude icon in the system tray and select "Quit", or run `pkill -f claude-desktop` from a terminal.
2948
2949 Simply closing the window does not fully quit the application, and your MCP server configuration changes will not take effect.
2950 </Warning>
2951
2952 **Tool calls failing silently**
2953
2954 If Claude attempts to use the tools but they fail:
2955
2956 1. Check Claude's logs for errors
2957 2. Verify your server builds and runs without errors
2958 3. Try restarting Claude for Desktop
2959
2960 **None of this is working. What do I do?**
2961
2962 Please refer to our [debugging guide](/docs/2026-07-28/tools/debugging) for better debugging tools and more detailed guidance.
2963 </Accordion>
2964
2965 <Accordion title="Weather API Issues">
2966 **Error: Failed to retrieve grid point data**
2967
2968 This usually means either:
2969
2970 1. The coordinates are outside the US
2971 2. The NWS API is having issues
2972 3. You're being rate limited
2973
2974 Fix:
2975
2976 * Verify you're using US coordinates
2977 * Add a small delay between requests
2978 * Check the NWS API status page
2979
2980 **Error: No active alerts for \[STATE]**
2981
2982 This isn't an error - it just means there are no current weather alerts for that state. Try a different state or check during severe weather.
2983 </Accordion>
2984</AccordionGroup>
2985
2986<Note>
2987 For more advanced troubleshooting, check out our guide on [Debugging MCP](/docs/2026-07-28/tools/debugging)
2988</Note>
2849> **Claude for Desktop Integration Issues**
2850>
2851> **Getting logs from Claude for Desktop**
2852>
2853> Claude.app logging related to MCP is written to log files in `~/Library/Logs/Claude` (macOS) or `~/.config/Claude/logs/` (Linux):
2854>
2855> * `mcp.log` will contain general logging about MCP connections and connection failures.
2856> * Files named `mcp-server-SERVERNAME.log` will contain the stderr output from the named server. Stdio servers may use stderr for all their logging, so these files are not limited to errors.
2857>
2858> You can run the following command to list recent logs and follow along with any new ones:
2859>
2860> ```bash macOS theme={null}
2861> # Check Claude's logs for errors
2862> tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
2863> ```
2864>
2865> ```bash Linux theme={null}
2866> # Check Claude's logs for errors
2867> tail -n 20 -f ~/.config/Claude/logs/mcp*.log
2868> ```
2869>
2870> **Server not showing up in Claude**
2871>
2872> 1. Check your `claude_desktop_config.json` file syntax
2873>
2874> 2. Make sure the path to your project is absolute and not relative
2875>
2876> 3. Restart Claude for Desktop completely
2877>
2878> > [!WARNING]
2879> >
2880> > To properly restart Claude for Desktop, you must fully quit the application:
2881> >
2882> > * **Windows**: Right-click the Claude icon in the system tray (which may be hidden in the "hidden icons" menu) and select "Quit" or "Exit".
2883> > * **macOS**: Use Cmd+Q or select "Quit Claude" from the menu bar.
2884> > * **Linux**: Right-click the Claude icon in the system tray and select "Quit", or run `pkill -f claude-desktop` from a terminal.
2885> >
2886> > Simply closing the window does not fully quit the application, and your MCP server configuration changes will not take effect.
2887>
2888> **Tool calls failing silently**
2889>
2890> If Claude attempts to use the tools but they fail:
2891>
2892> 1. Check Claude's logs for errors
2893> 2. Verify your server builds and runs without errors
2894> 3. Try restarting Claude for Desktop
2895>
2896> **None of this is working. What do I do?**
2897>
2898> Please refer to our [debugging guide](/docs/2026-07-28/tools/debugging) for better debugging tools and more detailed guidance.
2899
2900> **Weather API Issues**
2901>
2902> **Error: Failed to retrieve grid point data**
2903>
2904> This usually means either:
2905>
2906> 1. The coordinates are outside the US
2907> 2. The NWS API is having issues
2908> 3. You're being rate limited
2909>
2910> Fix:
2911>
2912> * Verify you're using US coordinates
2913> * Add a small delay between requests
2914> * Check the NWS API status page
2915>
2916> **Error: No active alerts for \[STATE]**
2917>
2918> This isn't an error - it just means there are no current weather alerts for that state. Try a different state or check during severe weather.
2919
2920> [!NOTE]
2921>
2922> For more advanced troubleshooting, check out our guide on [Debugging MCP](/docs/2026-07-28/tools/debugging)
29892923
29902924## Next steps
29912925
2992<CardGroup cols={2}>
2993 <Card title="Building a client" icon="outlet" href="/docs/2026-07-28/develop/build-client">
2994 Learn how to build your own MCP client that can connect to your server
2995 </Card>
2996
2997 <Card title="Example servers" icon="grid" href="/examples">
2998 Check out our gallery of official MCP servers and implementations
2999 </Card>
3000
3001 <Card title="Debugging Guide" icon="bug" href="/docs/2026-07-28/tools/debugging">
3002 Learn how to effectively debug MCP servers and integrations
3003 </Card>
3004
3005 <Card title="Build with Agent Skills" icon="comments" href="/docs/2026-07-28/develop/build-with-agent-skills">
3006 Use agent skills to guide AI coding assistants through server design
3007 </Card>
3008</CardGroup>
2926> **[Building a client](/docs/2026-07-28/develop/build-client)**
2927>
2928> Learn how to build your own MCP client that can connect to your server
2929
2930> **[Example servers](/examples)**
2931>
2932> Check out our gallery of official MCP servers and implementations
2933
2934> **[Debugging Guide](/docs/2026-07-28/tools/debugging)**
2935>
2936> Learn how to effectively debug MCP servers and integrations
2937
2938> **[Build with Agent Skills](/docs/2026-07-28/develop/build-with-agent-skills)**
2939>
2940> Use agent skills to guide AI coding assistants through server design
30092941
docs/2026-07-28/develop/build-with-agent-skills Changed · +9 / -11 lines
from line 85
8585Once your agent scaffolds the server, iterate on tool descriptions and error
8686handling, then test and ship:
8787
88<CardGroup cols={2}>
89 <Card title="MCP Inspector" icon="magnifying-glass" href="/docs/2026-07-28/tools/inspector">
90 Test your server's tools, resources, and prompts interactively
91 </Card>
88> **[MCP Inspector](/docs/2026-07-28/tools/inspector)**
89>
90> Test your server's tools, resources, and prompts interactively
9291
93 <Card title="Connect to a client" icon="plug" href="/docs/2026-07-28/develop/connect-local-servers">
94 Wire your server into an MCP client via local or remote configuration
95 </Card>
92> **[Connect to a client](/docs/2026-07-28/develop/connect-local-servers)**
93>
94> Wire your server into an MCP client via local or remote configuration
9695
97 <Card title="Publish to the Registry" icon="box" href="/registry/quickstart">
98 Make your server discoverable in the MCP Registry
99 </Card>
100</CardGroup>
96> **[Publish to the Registry](/registry/quickstart)**
97>
98> Make your server discoverable in the MCP Registry
10199
docs/2026-07-28/develop/connect-local-servers Changed · +188 / -212 lines
from line 6
66
77This guide demonstrates how to connect to local MCP servers using Claude Desktop as an example, one of the many clients that support MCP. While we focus on Claude Desktop's implementation, the concepts apply broadly to other MCP-compatible clients. By the end of this tutorial, Claude will be able to interact with files on your computer, create new documents, organize folders, and search through your file system—all with your explicit permission for each action.
88
9<Frame>
10 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-filesystem.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=629d7e754dc358d71a408d6ce970c1b1" alt="Claude Desktop with filesystem integration showing file management capabilities" width="1732" height="2060" data-path="images/quickstart-filesystem.png" />
11</Frame>
9
1210
1311## Prerequisites
1412
from line 43
4543
4644The process involves configuring Claude Desktop to automatically start the Filesystem Server whenever you launch the application. This configuration is done through a JSON file that tells Claude Desktop which servers to run and how to connect to them.
4745
48<Steps>
49 <Step title="Open Claude Desktop Settings">
50 Start by accessing the Claude Desktop settings. Click on the Claude menu in your system's menu bar (not the settings within the Claude window itself) and select "Settings..."
46**1. Open Claude Desktop Settings**
5147
52 On macOS, this appears in the top menu bar:
48Start by accessing the Claude Desktop settings. Click on the Claude menu in your system's menu bar (not the settings within the Claude window itself) and select "Settings..."
5349
54 <Frame style={{ textAlign: "center" }}>
55 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-menu.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=0c8b57e0e17af3624b6762a3ea944c8e" width="400" alt="Claude Desktop menu showing Settings option" data-path="images/quickstart-menu.png" />
56 </Frame>
50On macOS, this appears in the top menu bar:
5751
58 This opens the Claude Desktop configuration window, which is separate from your Claude account settings.
59 </Step>
52
6053
61 <Step title="Access Developer Settings">
62 In the Settings window, navigate to the "Developer" tab in the left sidebar. This section contains options for configuring MCP servers and other developer features.
54This opens the Claude Desktop configuration window, which is separate from your Claude account settings.
6355
64 Click the "Edit Config" button to open the configuration file:
56**2. Access Developer Settings**
6557
66 <Frame>
67 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-developer.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=0fb595490a2f9e15c0301e771a57446c" alt="Developer settings showing Edit Config button" width="1688" height="534" data-path="images/quickstart-developer.png" />
68 </Frame>
58In the Settings window, navigate to the "Developer" tab in the left sidebar. This section contains options for configuring MCP servers and other developer features.
6959
70 This action creates a new configuration file if one doesn't exist, or opens your existing configuration. The file is located at:
60Click the "Edit Config" button to open the configuration file:
7161
72 * **macOS**: `~/Library/Application Support/Claude/claude_desktop_config.json`
73 * **Windows**: `%APPDATA%\Claude\claude_desktop_config.json`
74 </Step>
62
7563
76 <Step title="Configure the Filesystem Server">
77 Replace the contents of the configuration file with the following JSON structure. This configuration tells Claude Desktop to start the Filesystem Server with access to specific directories:
64This action creates a new configuration file if one doesn't exist, or opens your existing configuration. The file is located at:
7865
79 <CodeGroup>
80 ```json macOS theme={null}
81 {
82 "mcpServers": {
83 "filesystem": {
84 "command": "npx",
85 "args": [
86 "-y",
87 "@modelcontextprotocol/server-filesystem",
88 "/Users/username/Desktop",
89 "/Users/username/Downloads"
90 ]
91 }
92 }
93 }
94 ```
66* **macOS**: `~/Library/Application Support/Claude/claude_desktop_config.json`
67* **Windows**: `%APPDATA%\Claude\claude_desktop_config.json`
9568
96 ```json Windows theme={null}
97 {
98 "mcpServers": {
99 "filesystem": {
100 "command": "npx",
101 "args": [
102 "-y",
103 "@modelcontextprotocol/server-filesystem",
104 "C:\\Users\\username\\Desktop",
105 "C:\\Users\\username\\Downloads"
106 ]
107 }
108 }
109 }
110 ```
111 </CodeGroup>
69**3. Configure the Filesystem Server**
11270
113 Replace `username` with your actual computer username. The paths listed in the `args` array specify which directories the Filesystem Server can access. You can modify these paths or add additional directories as needed.
71Replace the contents of the configuration file with the following JSON structure. This configuration tells Claude Desktop to start the Filesystem Server with access to specific directories:
11472
115 <Tip>
116 **Understanding the Configuration**
73```json macOS theme={null}
74{
75 "mcpServers": {
76 "filesystem": {
77 "command": "npx",
78 "args": [
79 "-y",
80 "@modelcontextprotocol/server-filesystem",
81 "/Users/username/Desktop",
82 "/Users/username/Downloads"
83 ]
84 }
85 }
86}
87```
11788
118 * `"filesystem"`: A friendly name for the server that appears in Claude Desktop
119 * `"command": "npx"`: Uses Node.js's npx tool to run the server
120 * `"-y"`: Automatically confirms the installation of the server package
121 * `"@modelcontextprotocol/server-filesystem"`: The package name of the Filesystem Server
122 * The remaining arguments: Directories the server is allowed to access
123 </Tip>
89```json Windows theme={null}
90{
91 "mcpServers": {
92 "filesystem": {
93 "command": "npx",
94 "args": [
95 "-y",
96 "@modelcontextprotocol/server-filesystem",
97 "C:\\Users\\username\\Desktop",
98 "C:\\Users\\username\\Downloads"
99 ]
100 }
101 }
102}
103```
124104
125 <Warning>
126 **Security Consideration**
105Replace `username` with your actual computer username. The paths listed in the `args` array specify which directories the Filesystem Server can access. You can modify these paths or add additional directories as needed.
127106
128 Only grant access to directories you're comfortable with Claude reading and modifying. The server runs with your user account permissions, so it can perform any file operations you can perform manually.
129 </Warning>
130 </Step>
107> [!TIP]
108>
109> **Understanding the Configuration**
110>
111> * `"filesystem"`: A friendly name for the server that appears in Claude Desktop
112> * `"command": "npx"`: Uses Node.js's npx tool to run the server
113> * `"-y"`: Automatically confirms the installation of the server package
114> * `"@modelcontextprotocol/server-filesystem"`: The package name of the Filesystem Server
115> * The remaining arguments: Directories the server is allowed to access
131116
132 <Step title="Restart Claude Desktop">
133 After saving the configuration file, completely quit Claude Desktop and restart it. The application needs to restart to load the new configuration and start the MCP server.
117> [!WARNING]
118>
119> **Security Consideration**
120>
121> Only grant access to directories you're comfortable with Claude reading and modifying. The server runs with your user account permissions, so it can perform any file operations you can perform manually.
134122
135 Upon successful restart, click the "Add files, connectors, and more /" indicator <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/claude-add-files-connectors-and-more.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=53acf21f6807dd5323b70b84b5d98d8a" style={{display: 'inline', margin: 0, height: '1.3em', width: 'auto'}} width="33" height="33" data-path="images/claude-add-files-connectors-and-more.png" /> in the bottom-left corner of the conversation input box:
123**4. Restart Claude Desktop**
136124
137 <Frame>
138 <img src="https://mintcdn.com/mcp/akpggzunDlIcY2im/images/quickstart-slider.png?fit=max&auto=format&n=akpggzunDlIcY2im&q=85&s=a1ebd4259cff2a7472171885f2edc035" alt="Claude Desktop interface showing MCP server indicator" width="1414" height="410" data-path="images/quickstart-slider.png" />
139 </Frame>
125After saving the configuration file, completely quit Claude Desktop and restart it. The application needs to restart to load the new configuration and start the MCP server.
140126
141 Click on this indicator, then move the mouse over "Connectors" and click "Manage connectors". Select "filesystem" from the connector list to view the Filesystem Server's available tools:
127Upon successful restart, click the "Add files, connectors, and more /" indicator  in the bottom-left corner of the conversation input box:
142128
143 <Frame style={{ textAlign: "center" }}>
144 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-tools.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=212a63d76daba170d52db0d2f6f582be" width="400" alt="Available filesystem tools in Claude Desktop" data-path="images/quickstart-tools.png" />
145 </Frame>
129
146130
147 If the Filesystem Server doesn't connect, refer to the [Troubleshooting](#troubleshooting) section for debugging steps.
148 </Step>
149</Steps>
131Click on this indicator, then move the mouse over "Connectors" and click "Manage connectors". Select "filesystem" from the connector list to view the Filesystem Server's available tools:
150132
133
134
135If the Filesystem Server doesn't connect, refer to the [Troubleshooting](#troubleshooting) section for debugging steps.
136
151137## Using the Filesystem Server
152138
153139With the Filesystem Server connected, Claude can now interact with your file system. Try these example requests to explore the capabilities:
from line 148
162148
163149Before executing any file system operation, Claude will request your approval. This ensures you maintain control over all actions:
164150
165<Frame style={{ textAlign: "center" }}>
166 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-approve.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=98cc6e9dfe885fbd6e9bfae40601e494" width="500" alt="Claude requesting approval to perform a file operation" data-path="images/quickstart-approve.png" />
167</Frame>
151
168152
169153Review each request carefully before approving. You can always deny a request if you're not comfortable with the proposed action.
170154
from line 156
172156
173157If you encounter issues setting up or using the Filesystem Server, these solutions address common problems:
174158
175<AccordionGroup>
176 <Accordion title="Server not showing up in Claude / hammer icon missing">
177 1. Restart Claude Desktop completely
178 2. Check your `claude_desktop_config.json` file syntax
179 3. Make sure the file paths included in `claude_desktop_config.json` are valid and that they are absolute and not relative
180 4. Look at [logs](#getting-logs-from-claude-for-desktop) to see why the server is not connecting
181 5. In your command line, try manually running the server (replacing `username` as you did in `claude_desktop_config.json`) to see if you get any errors:
159> **Server not showing up in Claude / hammer icon missing**
160>
161> 1. Restart Claude Desktop completely
162> 2. Check your `claude_desktop_config.json` file syntax
163> 3. Make sure the file paths included in `claude_desktop_config.json` are valid and that they are absolute and not relative
164> 4. Look at [logs](#getting-logs-from-claude-for-desktop) to see why the server is not connecting
165> 5. In your command line, try manually running the server (replacing `username` as you did in `claude_desktop_config.json`) to see if you get any errors:
166>
167> ```bash macOS/Linux theme={null}
168> npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /Users/username/Downloads
169> ```
170>
171> ```powershell Windows theme={null}
172> npx -y @modelcontextprotocol/server-filesystem C:\Users\username\Desktop C:\Users\username\Downloads
173> ```
182174
183 <CodeGroup>
184 ```bash macOS/Linux theme={null}
185 npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /Users/username/Downloads
186 ```
175> **Getting logs from Claude Desktop**
176>
177> Claude.app logging related to MCP is written to log files in:
178>
179> * macOS: `~/Library/Logs/Claude`
180>
181> * Windows: `%APPDATA%\Claude\logs`
182>
183> * `mcp.log` will contain general logging about MCP connections and connection failures.
184>
185> * Files named `mcp-server-SERVERNAME.log` will contain the stderr output from the named server. Stdio servers may use stderr for all their logging, so these files are not limited to errors.
186>
187> You can run the following command to list recent logs and follow along with any new ones (on Windows, it will only show recent logs):
188>
189> ```bash macOS/Linux theme={null}
190> tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
191> ```
192>
193> ```powershell Windows theme={null}
194> type "%APPDATA%\Claude\logs\mcp*.log"
195> ```
187196
188 ```powershell Windows theme={null}
189 npx -y @modelcontextprotocol/server-filesystem C:\Users\username\Desktop C:\Users\username\Downloads
190 ```
191 </CodeGroup>
192 </Accordion>
197> **Tool calls failing silently**
198>
199> If Claude attempts to use the tools but they fail:
200>
201> 1. Check Claude's logs for errors
202> 2. Verify your server builds and runs without errors
203> 3. Try restarting Claude Desktop
193204
194 <Accordion title="Getting logs from Claude Desktop">
195 Claude.app logging related to MCP is written to log files in:
205> **None of this is working. What do I do?**
206>
207> Please refer to our [debugging guide](/docs/2026-07-28/tools/debugging) for better debugging tools and more detailed guidance.
196208
197 * macOS: `~/Library/Logs/Claude`
209> **ENOENT error and `$\{APPDATA\}` in paths on Windows**
210>
211> If your configured server fails to load, and you see within its logs an error referring to `${APPDATA}` within a path, you may need to add the expanded value of `%APPDATA%` to your `env` key in `claude_desktop_config.json`:
212>
213> ```json theme={null}
214> {
215> "brave-search": {
216> "command": "npx",
217> "args": ["-y", "@modelcontextprotocol/server-brave-search"],
218> "env": {
219> "APPDATA": "C:\\Users\\user\\AppData\\Roaming\\",
220> "BRAVE_API_KEY": "..."
221> }
222> }
223> }
224> ```
225>
226> With this change in place, launch Claude Desktop once again.
227>
228> > [!WARNING]
229> >
230> > **npm should be installed globally**
231> >
232> > The `npx` command may continue to fail if you have not installed npm globally. If npm is already installed globally, you will find `%APPDATA%\npm` exists on your system. If not, you can install npm globally by running the following command:
233> >
234> > ```bash theme={null}
235> > npm install -g npm
236> > ```
198237
199 * Windows: `%APPDATA%\Claude\logs`
200
201 * `mcp.log` will contain general logging about MCP connections and connection failures.
202
203 * Files named `mcp-server-SERVERNAME.log` will contain the stderr output from the named server. Stdio servers may use stderr for all their logging, so these files are not limited to errors.
204
205 You can run the following command to list recent logs and follow along with any new ones (on Windows, it will only show recent logs):
206
207 <CodeGroup>
208 ```bash macOS/Linux theme={null}
209 tail -n 20 -f ~/Library/Logs/Claude/mcp*.log
210 ```
211
212 ```powershell Windows theme={null}
213 type "%APPDATA%\Claude\logs\mcp*.log"
214 ```
215 </CodeGroup>
216 </Accordion>
217
218 <Accordion title="Tool calls failing silently">
219 If Claude attempts to use the tools but they fail:
220
221 1. Check Claude's logs for errors
222 2. Verify your server builds and runs without errors
223 3. Try restarting Claude Desktop
224 </Accordion>
225
226 <Accordion title="None of this is working. What do I do?">
227 Please refer to our [debugging guide](/docs/2026-07-28/tools/debugging) for better debugging tools and more detailed guidance.
228 </Accordion>
229
230 <Accordion title="ENOENT error and `${APPDATA}` in paths on Windows">
231 If your configured server fails to load, and you see within its logs an error referring to `${APPDATA}` within a path, you may need to add the expanded value of `%APPDATA%` to your `env` key in `claude_desktop_config.json`:
232
233 ```json theme={null}
234 {
235 "brave-search": {
236 "command": "npx",
237 "args": ["-y", "@modelcontextprotocol/server-brave-search"],
238 "env": {
239 "APPDATA": "C:\\Users\\user\\AppData\\Roaming\\",
240 "BRAVE_API_KEY": "..."
241 }
242 }
243 }
244 ```
245
246 With this change in place, launch Claude Desktop once again.
247
248 <Warning>
249 **npm should be installed globally**
250
251 The `npx` command may continue to fail if you have not installed npm globally. If npm is already installed globally, you will find `%APPDATA%\npm` exists on your system. If not, you can install npm globally by running the following command:
252
253 ```bash theme={null}
254 npm install -g npm
255 ```
256 </Warning>
257 </Accordion>
258</AccordionGroup>
259
260238## Next Steps
261239
262240Now that you've successfully connected Claude Desktop to a local MCP server, explore these options to expand your setup:
263241
264<CardGroup cols={2}>
265 <Card title="Explore other servers" icon="grid" href="https://github.com/modelcontextprotocol/servers">
266 Browse our collection of official and community-created MCP servers for
267 additional capabilities
268 </Card>
242> **[Explore other servers](https://github.com/modelcontextprotocol/servers)**
243>
244> Browse our collection of official and community-created MCP servers for
245> additional capabilities
269246
270 <Card title="Build your own server" icon="code" href="/docs/2026-07-28/develop/build-server">
271 Create custom MCP servers tailored to your specific workflows and
272 integrations
273 </Card>
247> **[Build your own server](/docs/2026-07-28/develop/build-server)**
248>
249> Create custom MCP servers tailored to your specific workflows and
250> integrations
274251
275 <Card title="Connect to remote servers" icon="cloud" href="/docs/2026-07-28/develop/connect-remote-servers">
276 Learn how to connect Claude to remote MCP servers for cloud-based tools and
277 services
278 </Card>
252> **[Connect to remote servers](/docs/2026-07-28/develop/connect-remote-servers)**
253>
254> Learn how to connect Claude to remote MCP servers for cloud-based tools and
255> services
279256
280 <Card title="Understand the protocol" icon="book" href="/docs/2026-07-28/learn/architecture">
281 Dive deeper into how MCP works and its architecture
282 </Card>
283</CardGroup>
257> **[Understand the protocol](/docs/2026-07-28/learn/architecture)**
258>
259> Dive deeper into how MCP works and its architecture
284260
docs/2026-07-28/develop/connect-remote-servers Changed · +46 / -62 lines
from line 25
2525
2626The process of connecting Claude to a remote MCP server involves adding a Custom Connector through the [Claude interface](https://claude.ai/). This establishes a secure connection between Claude and your chosen remote server.
2727
28<Steps>
29 <Step title="Navigate to Connector Settings">
30 Open Claude Desktop or Claude in your browser, then navigate to the settings page:
28**1. Navigate to Connector Settings**
3129
32 * **Desktop**: Either use the keyboard shortcut `Ctrl+Comma` or click the top-left menu icon <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/claude-desktop-hamburger-menu-icon.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=66e498f668362c79f829a07b5ce863c8" style={{display: 'inline', margin: 0, height: '1.3em', width: 'auto'}} width="33" height="33" data-path="images/claude-desktop-hamburger-menu-icon.png" />, hover over "File", and select "Settings"
33 * **Browser**: Either use the keyboard shortcut `⌘⇧,` (*macOS*) or click on your profile icon, and select "Settings" from the menu
30Open Claude Desktop or Claude in your browser, then navigate to the settings page:
3431
35 Once you're in the settings page, click "Connectors" in the sidebar. This displays your currently configured connectors and provides options for adding new ones.
36 </Step>
32* **Desktop**: Either use the keyboard shortcut `Ctrl+Comma` or click the top-left menu icon , hover over "File", and select "Settings"
33* **Browser**: Either use the keyboard shortcut `⌘⇧,` (*macOS*) or click on your profile icon, and select "Settings" from the menu
3734
38 <Step title="Add a Custom Connector">
39 In the Connectors section, click the "Add" button at the top-right of the window, then select "Add custom connector" from the dropdown. This begins the connection process. To follow along, copy/paste the URL below:
35Once you're in the settings page, click "Connectors" in the sidebar. This displays your currently configured connectors and provides options for adding new ones.
4036
41 ```text Example Remote Server theme={null}
42 https://example-server.modelcontextprotocol.io/mcp
43 ```
37**2. Add a Custom Connector**
4438
45 <Frame>
46 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-remote/1-add-connector.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=b5ae9b23164875bbaa3aff4c178cdc64" alt="Add custom connector button in Claude settings" width="1038" height="809" data-path="images/quickstart-remote/1-add-connector.png" />
47 </Frame>
39In the Connectors section, click the "Add" button at the top-right of the window, then select "Add custom connector" from the dropdown. This begins the connection process. To follow along, copy/paste the URL below:
4840
49 A dialog will appear prompting you to enter the remote MCP server URL. This URL should be provided by the server developer or administrator. Enter the complete URL, ensuring it includes the proper protocol (https\://) and any necessary path components.
41```text Example Remote Server theme={null}
42https://example-server.modelcontextprotocol.io/mcp
43```
5044
51 <Frame>
52 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-remote/2-connect.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=0934f16d8e016cade8e560c8f89d011b" alt="Dialog for entering remote MCP server URL" width="1616" height="282" data-path="images/quickstart-remote/2-connect.png" />
53 </Frame>
45
5446
55 After entering the URL, click "Add" to proceed with the connection.
56 </Step>
47A dialog will appear prompting you to enter the remote MCP server URL. This URL should be provided by the server developer or administrator. Enter the complete URL, ensuring it includes the proper protocol (https\://) and any necessary path components.
5748
58 <Step title="Complete Authentication">
59 Most remote MCP servers require authentication to ensure secure access to their resources. The authentication process varies depending on the server implementation but commonly involves OAuth, API keys, or username/password combinations.
49
6050
61 <Frame>
62 <img src="https://mintcdn.com/mcp/4ZXF1PrDkEaJvXpn/images/quickstart-remote/3-auth.png?fit=max&auto=format&n=4ZXF1PrDkEaJvXpn&q=85&s=89af6e1b85718637231388697cc7b015" alt="Authentication screen for remote MCP server" width="490" height="806" data-path="images/quickstart-remote/3-auth.png" />
63 </Frame>
51After entering the URL, click "Add" to proceed with the connection.
6452
65 Follow the authentication prompts provided by the server. This may redirect you to a third-party authentication provider or display a form within Claude. Once authentication is complete, Claude will establish a secure connection to the remote server.
66 </Step>
53**3. Complete Authentication**
6754
68 <Step title="Access Resources and Prompts">
69 After successful connection, the remote server’s resources and prompts become available in your Claude conversations. You can access these by clicking the "Add files, connectors, and more /" indicator <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/claude-add-files-connectors-and-more.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=53acf21f6807dd5323b70b84b5d98d8a" style={{display: 'inline', margin: 0, height: '1.3em', width: 'auto'}} width="33" height="33" data-path="images/claude-add-files-connectors-and-more.png" /> in the bottom-left corner of the message input area. Then hover over "Connectors", move the cursor over "Add to Example Remote Server", where hovering displays the attachment menu.
55Most remote MCP servers require authentication to ensure secure access to their resources. The authentication process varies depending on the server implementation but commonly involves OAuth, API keys, or username/password combinations.
7056
71 <Frame>
72 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-remote/4-select-resources-menu.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=e5fa85174f8acbadbd709bac66f42d5c" alt="Attachment menu showing available resources" width="735" height="378" data-path="images/quickstart-remote/4-select-resources-menu.png" />
73 </Frame>
57
7458
75 The menu displays all available resources and prompts from your connected server. Select the items you want to include in your conversation. These resources provide Claude with context and information from your external tools.
59Follow the authentication prompts provided by the server. This may redirect you to a third-party authentication provider or display a form within Claude. Once authentication is complete, Claude will establish a secure connection to the remote server.
7660
77 <Frame>
78 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-remote/5-select-prompts-resources.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=68722669d9e18252756885c703e4f221" alt="Selecting specific resources and prompts from the menu" width="648" height="529" data-path="images/quickstart-remote/5-select-prompts-resources.png" />
79 </Frame>
80 </Step>
61**4. Access Resources and Prompts**
8162
82 <Step title="Configure Tool Permissions">
83 Remote MCP servers often expose multiple tools with varying capabilities. You can control which tools Claude is allowed to use by configuring permissions in the connector settings. This ensures Claude only performs actions you've explicitly authorized.
63After successful connection, the remote server’s resources and prompts become available in your Claude conversations. You can access these by clicking the "Add files, connectors, and more /" indicator  in the bottom-left corner of the message input area. Then hover over "Connectors", move the cursor over "Add to Example Remote Server", where hovering displays the attachment menu.
8464
85 <Frame>
86 <img src="https://mintcdn.com/mcp/cpXzQjUOzyH0mCNH/images/quickstart-remote/6-configure-tools.png?fit=max&auto=format&n=cpXzQjUOzyH0mCNH&q=85&s=5cfd8b2c5d06e7e3699eac24c68d090e" alt="Tool permission configuration interface" width="604" height="745" data-path="images/quickstart-remote/6-configure-tools.png" />
87 </Frame>
65
8866
89 Navigate back to the Connectors settings and click on your connected server. Here you can enable or disable specific tools, set usage limits, and configure other security parameters according to your needs.
90 </Step>
91</Steps>
67The menu displays all available resources and prompts from your connected server. Select the items you want to include in your conversation. These resources provide Claude with context and information from your external tools.
9268
69
70
71**5. Configure Tool Permissions**
72
73Remote MCP servers often expose multiple tools with varying capabilities. You can control which tools Claude is allowed to use by configuring permissions in the connector settings. This ensures Claude only performs actions you've explicitly authorized.
74
75
76
77Navigate back to the Connectors settings and click on your connected server. Here you can enable or disable specific tools, set usage limits, and configure other security parameters according to your needs.
78
9379## Best Practices for Using Remote MCP Servers
9480
9581When working with remote MCP servers, consider these recommendations to ensure a secure and efficient experience:
from line 88
10288
10389Now that you've connected Claude to a remote MCP server, you can explore its capabilities in your conversations. Try using the connected tools to automate tasks, access external data, or integrate with your existing workflows.
10490
105<CardGroup cols={2}>
106 <Card title="Build your own remote server" icon="cloud" href="/docs/2026-07-28/develop/build-server">
107 Create custom remote MCP servers to integrate with proprietary tools and
108 services
109 </Card>
91> **[Build your own remote server](/docs/2026-07-28/develop/build-server)**
92>
93> Create custom remote MCP servers to integrate with proprietary tools and
94> services
11095
111 <Card title="Explore available servers" icon="grid" href="https://github.com/modelcontextprotocol/servers">
112 Browse our collection of official and community-created MCP servers
113 </Card>
96> **[Explore available servers](https://github.com/modelcontextprotocol/servers)**
97>
98> Browse our collection of official and community-created MCP servers
11499
115 <Card title="Connect local servers" icon="computer" href="/docs/2026-07-28/develop/connect-local-servers">
116 Learn how to connect Claude Desktop to local MCP servers for direct system
117 access
118 </Card>
100> **[Connect local servers](/docs/2026-07-28/develop/connect-local-servers)**
101>
102> Learn how to connect Claude Desktop to local MCP servers for direct system
103> access
119104
120 <Card title="Understand the architecture" icon="book" href="/docs/2026-07-28/learn/architecture">
121 Dive deeper into how MCP works and its architecture
122 </Card>
123</CardGroup>
105> **[Understand the architecture](/docs/2026-07-28/learn/architecture)**
106>
107> Dive deeper into how MCP works and its architecture
124108
125109Remote MCP servers unlock powerful possibilities for extending Claude's capabilities. As you become familiar with these integrations, you'll discover new ways to streamline your workflows and accomplish complex tasks more efficiently.
126110