936 pages for error.
Titles and paths first, then pages whose text carries it. Each row opens that page as this site last read it.
Connect to local MCP servers
Model Context Protocol · in the page
docs/2025-11-25/develop/connect-local-servers
…me` as you did in `claude_desktop_config.json`) to see if you get any errors: > > ```bash macOS/Linux theme={null} > npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /Users/usern…
Architecture overview
Model Context Protocol · in the page
docs/2025-11-25/learn/architecture
…r 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 conne…
Versioning
Model Context Protocol · in the page
docs/2025-11-25/learn/versioning
…le version to use for the session. The protocol provides appropriate error handling if version negotiation fails, allowing clients to gracefully terminate connections when they cannot find a version…
Debugging
Model Context Protocol · in the page
docs/2025-11-25/tools/debugging
…5/basic/transports.md#stdio), all messages logged to stderr (standard error) will be captured by the host application automatically. > [!WARNING] > > Local MCP servers should not log messages to stdo…
MCP Inspector
Model Context Protocol · in the page
docs/2025-11-25/tools/inspector
…* Missing prompt arguments * Concurrent operations * Verify error handling and error responses ## Next steps > [card] [Inspector Repository](https://github.com/modelcontextprotocol/inspect…
Understanding Authorization in MCP
Model Context Protocol · in the page
docs/2025-11-25/tutorials/security/authorization
…data.introspection_endpoint; > > if (!endpoint) { > console.error("[auth] no introspection endpoint in metadata"); > throw new Error("No token verification endpoint available in metada…
Security Best Practices
Model Context Protocol · in the page
docs/2025-11-25/tutorials/security/security_best_practices
…Internal-->>Client: Cloud credentials/metadata Note over Client: Error or response details leak to attacker Client->>MCP: Subsequent request with error details ``` #### Risks * **Credential…
Build an MCP client
Model Context Protocol · in the page
docs/2026-07-28/develop/build-client
…h(".js"): > command = "node" > else: > raise ValueError("Server script must be a .py or .js file") > > return StdioServerParameters(command=command, args=[server_script_path])…
Build an MCP server
Model Context Protocol · in the page
docs/2026-07-28/develop/build-server
…[str, Any] | None: > """Make a request to the NWS API with proper error handling.""" > headers = {"User-Agent": USER_AGENT, "Accept": "application/geo+json"} > async with httpx2.AsyncClien…
Build with Agent Skills
Model Context Protocol · in the page
docs/2026-07-28/develop/build-with-agent-skills
…nce your agent scaffolds the server, iterate on tool descriptions and error handling, then test and ship: > [card] [MCP Inspector](https://modelcontextprotocol.io/docs/2026-07-28/tools/inspector.md)…
Client Best Practices
Model Context Protocol · in the page
docs/2026-07-28/develop/clients/client-best-practices
…ring; level: string; } function logging_getLogs(input: { level: "error" | "warn" | "info"; since: number; }): Promise<{ entries: LogEntry[] }> { return mcp.callTool<{ entries: LogEntry[] }>("…
Connect to local MCP servers
Model Context Protocol · in the page
docs/2026-07-28/develop/connect-local-servers
…me` as you did in `claude_desktop_config.json`) to see if you get any errors: > > ```bash macOS/Linux theme={null} > npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /Users/usern…
Architecture overview
Model Context Protocol · in the page
docs/2026-07-28/learn/architecture
…ed version, it rejects the request with an `UnsupportedProtocolVersionError` listing the versions it does support, and the client retries with a mutually supported version. 2. **Capability Discovery*…
Versioning
Model Context Protocol · in the page
docs/2026-07-28/learn/versioning
…he requested version, it responds with an [`UnsupportedProtocolVersionError`](https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning#protocol-version-negotiation) listing the versio…
Debugging
Model Context Protocol · in the page
docs/2026-07-28/tools/debugging
…8/basic/transports/stdio.md), all messages logged to stderr (standard error) will be captured by the host application automatically. > [!WARNING] > > Local MCP servers should not log messages to stdo…
MCP Inspector
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector
…g:** `--web` (default), `--cli`, or `--tui`. At most one; passing two errors with `Specify at most one of --web, --cli, or --tui.` 2. **`-h` / `--help`.** Everything else (`--catalog`, `--config`, `-…
Authorization
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/authorization
…e over plaintext `http`, > so a non-loopback host is rejected with an error and there is no flag to > override that. If your browser runs on a different machine, forward the > callback port to it, or…
CLI client
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/cli
…dable UI resource, malformed `resourceUri`) is reported in a `resourceError` field rather than aborting, so one bad tool never kills a whole listing. The CLI can't render an App, so by default it doe…
Configuration and flags
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/configuration
…migrated. | | **Missing file?** | Created and seeded (see below). | **Errors.** | | **Default** | `~/.mcp-inspector/mcp.json`, or the `MCP_CATALOG_PATH` environment variable. | None; you must pass it.…
mcpdo connection client
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/mcpdo
…t or an agent, where stdin is not a TTY, an unqualified command is an error, so that a background job never acts on whichever server you last used. Set `MCP_ALLOW_DEFAULT_CONNECTION=1` to allow the fa…
Protocol eras
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/protocol-eras
…ver.elicitInput` (the test servers' > `collect_elicitation` preset) **errors** on a 2026-07-28 connection, because > server-to-client requests aren't allowed there. MRTR is its modern > replacement.…
Recipes
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/recipes
…orm"]` | `data-app-status` | `idle`, then `loading`, then `ready` or `error` (on `error`, `data-app-error` carries the reason) | | `[data-testid="connection-status"]` | `data-status` | `disconnected`,…
Security
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/security
…(about 104 bytes on macOS, 108 on Linux) is refused up front with an error naming the variable to shorten. ### How it authenticates commands Every request must carry a bearer token. There is no una…
TUI client
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/tui
…missing mcp-inspector --tui --config mcp.json # read-only session, errors if absent ``` With neither `--catalog` nor `--config`, and no [ad-hoc target](https://modelcontextprotocol.io/docs/2026-07…
Web client
Model Context Protocol · in the page
docs/2026-07-28/tools/inspector/web
…pector/authorization.md#mid-session-re-authorization) or surfaces the error. * **Fetch Lists One Page at a Time**: when off, list results are auto-aggregated across pages on connect; when on, each lis…
Understanding Authorization in MCP
Model Context Protocol · in the page
docs/2026-07-28/tutorials/security/authorization
…must reject a response that leaves it out. The same check applies to error responses. If it fails, the client must not act on the error or display it. The client should also discard a response whose…
Security Best Practices
Model Context Protocol · in the page
docs/2026-07-28/tutorials/security/security_best_practices
…Internal-->>Client: Cloud credentials/metadata Note over Client: Error or response details leak to attacker Client->>MCP: Subsequent request with error details ``` #### Risks * **Credential…
Build an MCP client
Model Context Protocol · in the page
docs/draft/develop/build-client
…h(".js"): > command = "node" > else: > raise ValueError("Server script must be a .py or .js file") > > return StdioServerParameters(command=command, args=[server_script_path])…
Build an MCP server
Model Context Protocol · in the page
docs/draft/develop/build-server
…[str, Any] | None: > """Make a request to the NWS API with proper error handling.""" > headers = {"User-Agent": USER_AGENT, "Accept": "application/geo+json"} > async with httpx2.AsyncClien…
Build with Agent Skills
Model Context Protocol · in the page
docs/draft/develop/build-with-agent-skills
…nce your agent scaffolds the server, iterate on tool descriptions and error handling, then test and ship: > [card] [MCP Inspector](https://modelcontextprotocol.io/docs/draft/tools/inspector.md) > > T…
Client Best Practices
Model Context Protocol · in the page
docs/draft/develop/clients/client-best-practices
…ring; level: string; } function logging_getLogs(input: { level: "error" | "warn" | "info"; since: number; }): Promise<{ entries: LogEntry[] }> { return mcp.callTool<{ entries: LogEntry[] }>("…
Connect to local MCP servers
Model Context Protocol · in the page
docs/draft/develop/connect-local-servers
…me` as you did in `claude_desktop_config.json`) to see if you get any errors: > > ```bash macOS/Linux theme={null} > npx -y @modelcontextprotocol/server-filesystem /Users/username/Desktop /Users/usern…
Architecture overview
Model Context Protocol · in the page
docs/draft/learn/architecture
…ed version, it rejects the request with an `UnsupportedProtocolVersionError` listing the versions it does support, and the client retries with a mutually supported version. 2. **Capability Discovery*…
Versioning
Model Context Protocol · in the page
docs/draft/learn/versioning
…he requested version, it responds with an [`UnsupportedProtocolVersionError`](https://modelcontextprotocol.io/specification/draft/basic/versioning#protocol-version-negotiation) listing the versions it…
Debugging
Model Context Protocol · in the page
docs/draft/tools/debugging
…t/basic/transports/stdio.md), all messages logged to stderr (standard error) will be captured by the host application automatically. > [!WARNING] > > Local MCP servers should not log messages to stdo…
MCP Inspector
Model Context Protocol · in the page
docs/draft/tools/inspector
…g:** `--web` (default), `--cli`, or `--tui`. At most one; passing two errors with `Specify at most one of --web, --cli, or --tui.` 2. **`-h` / `--help`.** Everything else (`--catalog`, `--config`, `-…
Authorization
Model Context Protocol · in the page
docs/draft/tools/inspector/authorization
…e over plaintext `http`, > so a non-loopback host is rejected with an error and there is no flag to > override that. If your browser runs on a different machine, forward the > callback port to it, or…
CLI client
Model Context Protocol · in the page
docs/draft/tools/inspector/cli
…dable UI resource, malformed `resourceUri`) is reported in a `resourceError` field rather than aborting, so one bad tool never kills a whole listing. The CLI can't render an App, so by default it doe…
Configuration and flags
Model Context Protocol · in the page
docs/draft/tools/inspector/configuration
…migrated. | | **Missing file?** | Created and seeded (see below). | **Errors.** | | **Default** | `~/.mcp-inspector/mcp.json`, or the `MCP_CATALOG_PATH` environment variable. | None; you must pass it.…
mcpdo connection client
Model Context Protocol · in the page
docs/draft/tools/inspector/mcpdo
…t or an agent, where stdin is not a TTY, an unqualified command is an error, so that a background job never acts on whichever server you last used. Set `MCP_ALLOW_DEFAULT_CONNECTION=1` to allow the fa…
Protocol eras
Model Context Protocol · in the page
docs/draft/tools/inspector/protocol-eras
…ver.elicitInput` (the test servers' > `collect_elicitation` preset) **errors** on a 2026-07-28 connection, because > server-to-client requests aren't allowed there. MRTR is its modern > replacement.…
Recipes
Model Context Protocol · in the page
docs/draft/tools/inspector/recipes
…orm"]` | `data-app-status` | `idle`, then `loading`, then `ready` or `error` (on `error`, `data-app-error` carries the reason) | | `[data-testid="connection-status"]` | `data-status` | `disconnected`,…
Security
Model Context Protocol · in the page
docs/draft/tools/inspector/security
…(about 104 bytes on macOS, 108 on Linux) is refused up front with an error naming the variable to shorten. ### How it authenticates commands Every request must carry a bearer token. There is no una…
TUI client
Model Context Protocol · in the page
docs/draft/tools/inspector/tui
…missing mcp-inspector --tui --config mcp.json # read-only session, errors if absent ``` With neither `--catalog` nor `--config`, and no [ad-hoc target](https://modelcontextprotocol.io/docs/draft/t…
Web client
Model Context Protocol · in the page
docs/draft/tools/inspector/web
…pector/authorization.md#mid-session-re-authorization) or surfaces the error. * **Fetch Lists One Page at a Time**: when off, list results are auto-aggregated across pages on connect; when on, each lis…
Understanding Authorization in MCP
Model Context Protocol · in the page
docs/draft/tutorials/security/authorization
…must reject a response that leaves it out. The same check applies to error responses. If it fails, the client must not act on the error or display it. The client should also discard a response whose…
Security Best Practices
Model Context Protocol · in the page
docs/draft/tutorials/security/security_best_practices
…Internal-->>Client: Cloud credentials/metadata Note over Client: Error or response details leak to attacker Client->>MCP: Subsequent request with error details ``` #### Risks * **Credential…
Build an MCP App
Model Context Protocol · in the page
extensions/apps/build
…dy); }); expressApp.listen(3001, (err) => { if (err) { console.error("Error starting server:", err); process.exit(1); } console.log("Server listening on http://localhost:3001/mcp"); });…
Enterprise-Managed Authorization
Model Context Protocol · in the page
extensions/auth/enterprise-managed-authorization
…suing tokens. Employees who lack authorization receive an appropriate error — the MCP client never receives a token for unauthorized servers. 4. **Centralized revocation**: Revoking an employee's acc…
Extensions Overview
Model Context Protocol · in the page
extensions/overview
…k to core protocol behavior or reject the request with an appropriate error if the extension is mandatory. It's a good practice to document expected fallback behavior in your extension. For example,…