762 pages for error.

Protocol eras Model Context Protocol · in the page docs/2026-07-28/tools/inspector/protocol-eras …lect_elicitation` pattern (a server calling `server.elicitInput`) **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 …-form"]` | `data-app-status` | `ready` (on failure, `data-app-error` carries the reason) | | `[data-testid="connection-status"]` | `data-statu… TUI client Model Context Protocol · in the page docs/2026-07-28/tools/inspector/tui …client) mcp-inspector --tui --config mcp.json # read-only session, errors if absent ``` With neither `--catalog` nor `--config`, and no [ad-hoc target](/docs/2026-07-28/tools/inspector/configurati… Web client Model Context Protocol · in the page docs/2026-07-28/tools/inspector/web …mirrored `Mcp-Param-*` headers, excluded tools, and distinct `-32602` error panels, all covered in [Protocol eras](/docs/2026-07-28/tools/inspector/protocol-eras#tools-mirrored-headers-and-excluded-to… Understanding Authorization in MCP Model Context Protocol · in the page docs/2026-07-28/tutorials/security/authorization …a.introspection_endpoint; if (!endpoint) { console.error("[auth] no introspection endpoint in metadata"); throw new Error("No token verification endpoint available in meta… 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 …"): 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 …tr, 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.AsyncC… 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: <CardGroup cols={2}> <Card title="MCP Inspector" icon="magnifying-glass" href="/docs/draft/… 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: <CodeGroup> ```bash macOS/Linux theme={null} npx -y @modelcontextprotocol/server-filesystem /Users/userna… 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 Discov… Versioning Model Context Protocol · in the page docs/draft/learn/versioning …he requested version, it responds with an [`UnsupportedProtocolVersionError`](/specification/draft/basic/versioning#protocol-version-negotiation) listing the versions it does support. The client can t… Debugging Model Context Protocol · in the page docs/draft/tools/debugging …raft/basic/transports/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 stdout (s… 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; `--… 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. <Note> `tools/list --app-info` always emits NDJ… Configuration and flags Model Context Protocol · in the page docs/draft/tools/inspector/configuration …seeded (see below). | **Errors.** | | **Default** | `~/.mcp-inspector/mcp.json`, or the `MCP_C… Protocol eras Model Context Protocol · in the page docs/draft/tools/inspector/protocol-eras …lect_elicitation` pattern (a server calling `server.elicitInput`) **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 …-form"]` | `data-app-status` | `ready` (on failure, `data-app-error` carries the reason) | | `[data-testid="connection-status"]` | `data-statu… TUI client Model Context Protocol · in the page docs/draft/tools/inspector/tui …client) mcp-inspector --tui --config mcp.json # read-only session, errors if absent ``` With neither `--catalog` nor `--config`, and no [ad-hoc target](/docs/draft/tools/inspector/configuration#ad… Web client Model Context Protocol · in the page docs/draft/tools/inspector/web …mirrored `Mcp-Param-*` headers, excluded tools, and distinct `-32602` error panels, all covered in [Protocol eras](/docs/draft/tools/inspector/protocol-eras#tools-mirrored-headers-and-excluded-tools).… Understanding Authorization in MCP Model Context Protocol · in the page docs/draft/tutorials/security/authorization …a.introspection_endpoint; if (!endpoint) { console.error("[auth] no introspection endpoint in metadata"); throw new Error("No token verification endpoint available in meta… 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,… Skills Model Context Protocol · in the page extensions/skills/overview …ost->>Server: skills/get (URI) Server-->>Host: Skill entry or error end break Lookup failed Note over Host,Server: Stop loading (unknown skill: -32602) end Note over Ho… Tasks Model Context Protocol · in the page extensions/tasks/overview …s the current status and, for terminal states, the final result or error. 4. **Mid-flight input.** If the task moves to `input_required`, the `tasks/get` response includes an `inputRequests` ma… How to Automate Publishing with GitHub Actions Model Context Protocol · in the page registry/github-actions …m, and publish the server to the MCP Registry. ## Troubleshooting | Error Message | Action… Quickstart: Publish an MCP Server to the MCP Registry Model Context Protocol · in the page registry/quickstart …e":"io.github.my-username/weather" ... }]} ``` ## Troubleshooting | Error Message | Action… Versioning Published MCP Servers Model Context Protocol · in the page registry/versioning …wise be sorted before the semantic version strings. </Warning> As an error prevention mechanism, the MCP Registry prohibits version strings that appear to refer to ranges of versions. | Example… SEP-1036: URL Mode Elicitation for secure out-of-band interactions Model Context Protocol · in the page seps/1036-url-mode-elicitation-for-secure-out-of-band-intera …automatically retry requests that received a URL elicitation required error, update the user interface, or otherwise continue an interaction. However, because delivery of the notification is not guara… SEP-1319: Decouple Request Payload from RPC Methods Definition Model Context Protocol · in the page seps/1319-decouple-request-payload-from-rpc-methods-definiti …redundancy and making future updates to the protocol more complex and error-prone. * **Tightly Coupled to JSON-RPC:** Most critically, this tight coupling to JSON-RPC is the primary blocker for defini… SEP-1577: Sampling With Tools Model Context Protocol · in the page seps/1577--sampling-with-tools …### Protocol changes * `sampling/createMessage` * ~~MUST throw an error when `includeContext is “thisServer” | “allServers”` but `clientCapabilities.sampling.context` is missing~~ * MUST throw a… SEP-1686: Tasks Model Context Protocol · in the page seps/1686-tasks …not happen across many tools in a large toolset is time-consuming and error-prone. ***Ideal:*** Support natively polling tool state at the data layer to support pushing a tool to the background and av… SEP-1865: MCP Apps - Interactive User Interfaces for MCP Model Context Protocol · in the page seps/1865-mcp-apps-interactive-user-interfaces-for-mcp …itions, SDKs, etc.). JSON-RPC offers advanced capabilities (timeouts, errors, etc.). **Alternatives considered:** * **Custom message protocol:** Current MCP-UI approach with message types like tool,… SEP-2106: Tools `inputSchema` & `outputSchema` Conform to JSON Schema 2020-12 Model Context Protocol · in the page seps/2106-json-schema-2020-12 …n SDKs for MCP, has implemented extensive workarounds: 1. **Explicit error messages** acknowledge the limitation: ```python theme={null} raise ValueError( f"Output schemas must represen… SEP-2133: Extensions Model Context Protocol · in the page seps/2133-extensions …t to core protocol behavior or reject the request with an appropriate error if the extension is mandatory. Extensions SHOULD document their expected fallback behavior. For example, a server offering U… SEP-2243: HTTP Header Standardization for Streamable HTTP Transport Model Context Protocol · in the page seps/2243-http-standardization …e**: This requirement prevents potential security vulnerabilities and error conditions that could arise when different components in the network rely on different sources of truth. For example, a load… SEP-2260: Require Server requests to be associated with a Client request. Model Context Protocol · in the page seps/2260-Require-Server-requests-to-be-associated-with-Client-requests …outbound request **SHOULD** respond with a `-32602` (Invalid Params) error. ### For Transport Implementers Future transport implementations can rely on the guarantee that: * Sampling/elicitation r… SEP-2322: Multi Round-Trip Requests Model Context Protocol · in the page seps/2322-MRTR …erature: 72°F\nConditions: Partly cloudy" } ], "isError": false } } ``` </details> #### Real-World Example for Ephemeral Workflow This example demonstrates how `requestSt… SEP-2468: Recommend Issuer (iss) Parameter in MCP Auth Responses Model Context Protocol · in the page seps/2468-recommend-issuer-claim-for-auth …ude an issuer (*iss*) parameter in authorization responses, including error responses, as defined in [RFC9207](https://datatracker.ietf.org/doc/html/rfc9207#section-2). Authorization servers that do s… SEP-2549: TTL for List Results Model Context Protocol · in the page seps/2549-TTL-for-list-results …the TTL has not yet expired. Examples include receiving an unexpected error on a tool call indicating that the the method was not found or the parameters were invalid. Clients MAY serve stale respons… SEP-2567: Sessionless MCP via Explicit State Handles Model Context Protocol · in the page seps/2567-sessionless-mcp …ents and recommends — in the same way it might document pagination or error-message conventions — not something it implements. The normative content of this SEP is the removal in (1); (2) follows from… SEP-2575: Make MCP Stateless Model Context Protocol · in the page seps/2575-stateless-mcp …such as an experimental or draft version), it MUST return a JSON-RPC error response. For HTTP, the response status code MUST be `400 Bad Request`. The error MUST conform to the following structure:… SEP-2577: Deprecate Roots, Sampling, and Logging Model Context Protocol · in the page seps/2577-deprecate-roots-sampling-and-logging …— especially across multiple protocol versions — would be complex and error-prone. Deprecation followed by removal is less disruptive: implementations can continue using the features as-is during the… SEP-2640: Skills Extension Model Context Protocol · in the page seps/2640-skills-extension …a-skillsget) confirms, the server answering for a skill it serves and erroring otherwise. This holds for every scheme, `skill://` included. A host MUST NOT conclude that a resource is a skill merely b… SEP-2663: Tasks Extension Model Context Protocol · in the page seps/2663-tasks-extension …status, in-progress server-to-client requests, and a final result or error. Task creation is server-directed: the client signals support by including the extension in its per-request capabilities, an… SEP-986: Specify Format for Tool Names Model Context Protocol · in the page seps/986-specify-format-for-tool-names …casing, and character sets. This inconsistency can lead to confusion, errors in tool invocation, and difficulties in documentation and automation. Standardizing the allowed characters and length will:…