936 pages for error.

Key Changes Model Context Protocol · in the page specification/2026-07-28/changelog …ol/serverInfo`). Version mismatches return `UnsupportedProtocolVersionError` ([SEP-2575](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2575)). 3. Add `server/discover`: servers MU… Elicitation Model Context Protocol · in the page specification/2026-07-28/client/elicitation …ations with third-party services that require user authorization. ## Error Handling Servers **SHOULD NOT** assume that elicitation requests will always succeed, and **MUST** handle cases where the u… Roots Model Context Protocol · in the page specification/2026-07-28/client/roots …e/user/repos/backend", "name": "Backend Repository" } ] ``` ## Error Handling If an error occurs, the client does not need to replay the initial call with an error message as the server is not… Sampling Model Context Protocol · in the page specification/2026-07-28/client/sampling …ached. * `"toolUse"`: The model wants to use one or more tools. ## Error Handling If an error occurs or the user declines the sampling request, the client does not need to replay the initial call… Specification Model Context Protocol · in the page specification/2026-07-28/index …ional Utilities * Configuration * Progress tracking * Cancellation * Error reporting ### Extensions Beyond the core protocol, MCP defines optional [extensions](https://modelcontextprotocol.io/exten… Schema Reference Model Context Protocol · in the page specification/2026-07-28/schema …="schema-reference" /> ## JSON-RPC <div class="type"> ### `JSONRPCErrorResponse` <div class="tsd-signature"><span class="tsd-signature-keyword">interface</span> <span class="tsd-kind-interface"… Discovery Model Context Protocol · in the page specification/2026-07-28/server/discover …ient may invoke any RPC inline and handle [`UnsupportedProtocolVersionError`](https://modelcontextprotocol.io/specification/2026-07-28/schema#unsupportedprotocolversionerror) if the server does not su… Prompts Model Context Protocol · in the page specification/2026-07-28/server/prompts …or other reference materials directly into the conversation flow. ## Error Handling Servers **SHOULD** return standard JSON-RPC errors for common failure cases: * Invalid prompt name: `-32602` (Inv… Resources Model Context Protocol · in the page specification/2026-07-28/server/resources …f.org/doc/html/rfc3986), taking the above guidance in to account. ## Error Handling If the requested resource does not exist, servers **MUST** return a JSON-RPC error with code `-32602` (Invalid Par… Tools Model Context Protocol · in the page specification/2026-07-28/server/tools …\nTemperature: 72°F\nConditions: Partly cloudy" } ], "isError": false } } ``` ### Input Required Tool Results Servers **MAY** respond to `tools/call` with an [`InputRequiredResult`](… Caching Model Context Protocol · in the page specification/2026-07-28/server/utilities/caching …reason to believe the data has changed (e.g., receiving an unexpected error on a tool call indicating the method was not found or the parameters were invalid). Clients **MAY** serve stale responses i… Completion Model Context Protocol · in the page specification/2026-07-28/server/utilities/completion …l`: Optional total matches * `hasMore`: Additional results flag ## Error Handling Servers **SHOULD** return standard JSON-RPC errors for common failure cases: * Method not found: `-32601` (Capabi… Logging Model Context Protocol · in the page specification/2026-07-28/server/utilities/logging …anges | | warning | Warning conditions | Deprecated feature usage | | error | Error conditions | Operation failures | | critical | Critical conditions | System component failures | | alert | Action mu… Pagination Model Context Protocol · in the page specification/2026-07-28/server/utilities/pagination …rsor and thus **MUST NOT** be treated as the end of results) ## Error Handling Invalid cursors **SHOULD** result in an error with code -32602 (Invalid params). Client Registration Model Context Protocol · in the page specification/draft/basic/authorization/client-registration …ent: MCP responses else Validation Failure Server->>User: Error response<br/>error=invalid_client or invalid_request end Note over Server: Cache metadata for future requests<br/>(… Authorization Model Context Protocol · in the page specification/draft/basic/authorization/index …D** include the `iss` parameter in authorization responses, including error responses, as defined in [RFC9207 Section 2](https://datatracker.ietf.org/doc/html/rfc9207#section-2). Authorization servers… Overview Model Context Protocol · in the page specification/draft/basic/index …ponses are sent in reply to requests, containing either the result or error of the operation. #### Result Responses [Result responses](https://modelcontextprotocol.io/specification/draft/schema.md#j… Cancellation Model Context Protocol · in the page specification/draft/basic/patterns/cancellation …d resource exhaustion. When the request has not received a success or error response within the timeout period, the sender **SHOULD** cancel the request and stop waiting for a response. As described i… Overview Model Context Protocol · in the page specification/draft/basic/patterns/index …rver** answers each request with a JSON-RPC *response* (a result or error), optionally preceded by *notifications* scoped to that request. Servers **MUST NOT** initiate JSON-RPC requests, and clien… Multi Round-Trip Requests Model Context Protocol · in the page specification/draft/basic/patterns/mrtr …or any other request that the client may be sending in parallel. ### Error Handling Servers **SHOULD** validate that the data provided by the client is a valid `InputResponses` object and that the i… stdio Model Context Protocol · in the page specification/draft/basic/transports/stdio …tderr` for any logging purposes including informational, debug, and error messages. * The client **MAY** capture, forward, or ignore the server's `stderr` output and **SHOULD NOT** assume `stderr`… Streamable HTTP Model Context Protocol · in the page specification/draft/basic/transports/streamable-http …3 Forbidden. The HTTP response body **MAY** comprise a JSON-RPC *error response* that has no `id`. 2. When running locally, servers **SHOULD** bind only to localhost (127.0.0.1) rather than al… Versioning and Compatibility Model Context Protocol · in the page specification/draft/basic/versioning …rsion unsupported Server-->>Client: UnsupportedProtocolVersionError Note over Client,Server: Client retries with a mutually supported version end ``` ## Terminology This page use… Elicitation Model Context Protocol · in the page specification/draft/client/elicitation …ations with third-party services that require user authorization. ## Error Handling Servers **SHOULD NOT** assume that elicitation requests will always succeed, and **MUST** handle cases where the u… Roots Model Context Protocol · in the page specification/draft/client/roots …e/user/repos/backend", "name": "Backend Repository" } ] ``` ## Error Handling If an error occurs, the client does not need to replay the initial call with an error message as the server is not… Sampling Model Context Protocol · in the page specification/draft/client/sampling …ached. * `"toolUse"`: The model wants to use one or more tools. ## Error Handling If an error occurs or the user declines the sampling request, the client does not need to replay the initial call… Specification Model Context Protocol · in the page specification/draft/index …ional Utilities * Configuration * Progress tracking * Cancellation * Error reporting ### Extensions Beyond the core protocol, MCP defines optional [extensions](https://modelcontextprotocol.io/exten… Schema Reference Model Context Protocol · in the page specification/draft/schema …="schema-reference" /> ## JSON-RPC <div class="type"> ### `JSONRPCErrorResponse` <div class="tsd-signature"><span class="tsd-signature-keyword">interface</span> <span class="tsd-kind-interface"… Discovery Model Context Protocol · in the page specification/draft/server/discover …ient may invoke any RPC inline and handle [`UnsupportedProtocolVersionError`](https://modelcontextprotocol.io/specification/draft/schema#unsupportedprotocolversionerror) if the server does not support… Prompts Model Context Protocol · in the page specification/draft/server/prompts …or other reference materials directly into the conversation flow. ## Error Handling Servers **SHOULD** return standard JSON-RPC errors for common failure cases: * Invalid prompt name: `-32602` (Inv… Resources Model Context Protocol · in the page specification/draft/server/resources …f.org/doc/html/rfc3986), taking the above guidance in to account. ## Error Handling If the requested resource does not exist, servers **MUST** return a JSON-RPC error with code `-32602` (Invalid Par… Tools Model Context Protocol · in the page specification/draft/server/tools …\nTemperature: 72°F\nConditions: Partly cloudy" } ], "isError": false } } ``` ### Input Required Tool Results Servers **MAY** respond to `tools/call` with an [`InputRequiredResult`](… Caching Model Context Protocol · in the page specification/draft/server/utilities/caching …reason to believe the data has changed (e.g., receiving an unexpected error on a tool call indicating the method was not found or the parameters were invalid). Clients **MAY** serve stale responses i… Completion Model Context Protocol · in the page specification/draft/server/utilities/completion …l`: Optional total matches * `hasMore`: Additional results flag ## Error Handling Servers **SHOULD** return standard JSON-RPC errors for common failure cases: * Method not found: `-32601` (Capabi… Logging Model Context Protocol · in the page specification/draft/server/utilities/logging …anges | | warning | Warning conditions | Deprecated feature usage | | error | Error conditions | Operation failures | | critical | Critical conditions | System component failures | | alert | Action mu… Pagination Model Context Protocol · in the page specification/draft/server/utilities/pagination …rsor and thus **MUST NOT** be treated as the end of results) ## Error Handling Invalid cursors **SHOULD** result in an error with code -32602 (Invalid params).