762 pages for error.
Titles and paths first, then pages whose text carries it. Each row opens that page as this site last read it.
Lifecycle
Model Context Protocol · in the page
specification/2025-11-25/basic/lifecycle
…d resource exhaustion. When the request has not received a success or error response within the timeout period, the sender **SHOULD** issue a [cancellation notification](/specification/2025-11-25/basi…
Transports
Model Context Protocol · in the page
specification/2025-11-25/basic/transports
…ed newlines. * The server **MAY** write UTF-8 strings to its standard error (`stderr`) for any logging purposes including informational, debug, and error messages. * The client **MAY** capture, forw…
Cancellation
Model Context Protocol · in the page
specification/2025-11-25/basic/utilities/cancellation
…pplication UIs **SHOULD** indicate when cancellation is requested ## Error Handling Invalid cancellation notifications **SHOULD** be ignored: * Unknown request IDs * Already completed requests * Ma…
Ping
Model Context Protocol · in the page
specification/2025-11-25/basic/utilities/ping
…xcessive pinging **SHOULD** be avoided to reduce network overhead ## Error Handling * Timeouts **SHOULD** be treated as connection failures * Multiple failed pings **MAY** trigger connection reset *…
Tasks
Model Context Protocol · in the page
specification/2025-11-25/basic/utilities/tasks
…ol as a task. Servers **SHOULD** return a `-32601` (Method not found) error if a client attempts to do so. This is the default behavior. 2. If `execution.taskSupport` is `"optional"`, clients **MAY…
Key Changes
Model Context Protocol · in the page
specification/2025-11-25/changelog
…ing stdio transport may use stderr for all types of logging, not just error messages (PR [#670](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/670)). 2. Add optional `description` f…
Elicitation
Model Context Protocol · in the page
specification/2025-11-25/client/elicitation
…o automatically retry requests that received a [URLElicitationRequiredError](#error-handling), update the user interface, or otherwise continue an interaction. * **SHOULD** still provide manual contro…
Roots
Model Context Protocol · in the page
specification/2025-11-25/client/roots
…e/user/repos/backend", "name": "Backend Repository" } ] ``` ## Error Handling Clients **SHOULD** return standard JSON-RPC errors for common failure cases: * Client does not support roots: `-3…
Sampling
Model Context Protocol · in the page
specification/2025-11-25/client/sampling
…he sonnet hint to `gemini-1.5-pro` based on similar capabilities. ## Error Handling Clients **SHOULD** return errors for common failure cases: * User rejected sampling request: `-1` * Tool result m…
Specification
Model Context Protocol · in the page
specification/2025-11-25/index
…ional Utilities * Configuration * Progress tracking * Cancellation * Error reporting * Logging ## Security and Trust & Safety The Model Context Protocol enables powerful capabilities through arbitr…
Schema Reference
Model Context Protocol · in the page
specification/2025-11-25/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"…
Prompts
Model Context Protocol · in the page
specification/2025-11-25/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/2025-11-25/server/resources
…f.org/doc/html/rfc3986), taking the above guidance in to account. ## Error Handling Servers **SHOULD** return standard JSON-RPC errors for common failure cases: * Resource not found: `-32002` * Int…
Tools
Model Context Protocol · in the page
specification/2025-11-25/server/tools
…\nTemperature: 72°F\nConditions: Partly cloudy" } ], "isError": false } } ``` ### List Changed Notification When the list of available tools changes, servers that declared the `listC…
Completion
Model Context Protocol · in the page
specification/2025-11-25/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/2025-11-25/server/utilities/logging
…| Warning conditions | Deprecated feature usage | | error | Error conditions | Operation failures | | critical | Critical conditions | Syste…
Pagination
Model Context Protocol · in the page
specification/2025-11-25/server/utilities/pagination
…arse or modify cursors * Don't persist cursors across sessions ## Error Handling Invalid cursors **SHOULD** result in an error with code -32602 (Invalid params).
Client Registration
Model Context Protocol · in the page
specification/2026-07-28/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/2026-07-28/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/2026-07-28/basic/index
…ponses are sent in reply to requests, containing either the result or error of the operation. #### Result Responses [Result responses](/specification/2026-07-28/schema#jsonrpcresultresponse) are sen…
Cancellation
Model Context Protocol · in the page
specification/2026-07-28/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/2026-07-28/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/2026-07-28/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/2026-07-28/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/2026-07-28/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/2026-07-28/basic/versioning
…rsion unsupported Server-->>Client: UnsupportedProtocolVersionError Note over Client,Server: Client retries with a mutually supported version end ``` ## Terminology This page use…
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](/extensions/overview) that add modula…
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`](/specification/2026-07-28/schema#unsupportedprotocolversionerror) if the server does not support the requested version. Ho…
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
…| Warning conditions | Deprecated feature usage | | error | Error conditions | Operation failures | | critical | Critical conditions | Syste…
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](/specification/draft/schema#jsonrpcresultresponse) are sent whe…
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…