Debugging changeddocs/2025-03-26/tools/debugging
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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/2025-03-26/basic/transports#streamable-http),
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4848For all [transports](/specification/2025-03-26/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/2025-03-26/server/utilities/logging#log-levels)
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190188hover over the **Connectors** menu to see connected servers and available
191189tools.
192190
193<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" />
191
194192
195193### Viewing logs
196194
from line 197
199197* macOS: `~/Library/Logs/Claude`
200198* Windows: `%APPDATA%\Claude\logs`
201199
202<CodeGroup>
203 ```bash macOS theme={null}
204 tail -n 20 -F ~/Library/Logs/Claude/mcp*.log
205 ```
200```bash macOS theme={null}
201tail -n 20 -F ~/Library/Logs/Claude/mcp*.log
202```
206203
207 ```powershell Windows theme={null}
208 type "$env:AppData\Claude\logs\mcp*.log"
209 ```
210</CodeGroup>
204```powershell Windows theme={null}
205type "$env:AppData\Claude\logs\mcp*.log"
206```
211207
212208The logs capture:
213209
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223219
2242201. Create a `developer_settings.json` file with `allowDevTools` set to true:
225221
226<CodeGroup>
227 ```bash macOS theme={null}
228 echo '{"allowDevTools": true}' > ~/Library/Application\ Support/Claude/developer_settings.json
229 ```
222```bash macOS theme={null}
223echo '{"allowDevTools": true}' > ~/Library/Application\ Support/Claude/developer_settings.json
224```
230225
231 ```powershell Windows theme={null}
232 '{"allowDevTools": true}' | Set-Content "$env:AppData\Claude\developer_settings.json"
233 ```
234</CodeGroup>
226```powershell Windows theme={null}
227'{"allowDevTools": true}' | Set-Content "$env:AppData\Claude\developer_settings.json"
228```
235229
2362302. Open DevTools: `Command-Option-I` (macOS) or `Ctrl+Alt+I` (Windows)
237231
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332326
333327## Next steps
334328
335<CardGroup cols={2}>
336 <Card title="MCP Inspector" icon="magnifying-glass" href="/docs/2025-03-26/tools/inspector">
337 Learn to use the MCP Inspector
338 </Card>
329> **[MCP Inspector](/docs/2025-03-26/tools/inspector)**
330>
331> Learn to use the MCP Inspector
339332
340 <Card title="Build an MCP server" icon="code" href="/docs/2025-03-26/develop/build-server">
341 Walk through building a server from scratch
342 </Card>
333> **[Build an MCP server](/docs/2025-03-26/develop/build-server)**
334>
335> Walk through building a server from scratch
343336
344 <Card title="Connect local servers" icon="plug" href="/docs/2025-03-26/develop/connect-local-servers">
345 Full claude\_desktop\_config.json reference and troubleshooting
346 </Card>
347</CardGroup>
337> **[Connect local servers](/docs/2025-03-26/develop/connect-local-servers)**
338>
339> Full claude\_desktop\_config.json reference and troubleshooting
348340
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