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Architecture Model Context Protocol · in the page specification/2025-06-18/architecture/index …n-numbers" /> The Model Context Protocol (MCP) follows a client-host-server architecture where each host can run multiple client instances. This architecture enables users to integrate AI capabilitie… Authorization Model Context Protocol · in the page specification/2025-06-18/basic/authorization …nsport level, enabling MCP clients to make requests to restricted MCP servers on behalf of resource owners. This specification defines the authorization flow for HTTP-based transports. ### Protocol R… Overview Model Context Protocol · in the page specification/2025-06-18/basic/index …hentication and authorization framework for HTTP-based transports * **Server Features**: Resources, prompts, and tools exposed by servers * **Client Features**: Sampling and root directory lists provi… Lifecycle Model Context Protocol · in the page specification/2025-06-18/basic/lifecycle …Model Context Protocol (MCP) defines a rigorous lifecycle for client-server connections that ensures proper capability negotiation and state management. 1. **Initialization**: Capability negotiation… Transports Model Context Protocol · in the page specification/2025-06-18/basic/transports …otocol currently defines two standard transport mechanisms for client-server communication: 1. [stdio](#stdio), communication over standard in and standard out 2. [Streamable HTTP](#streamable-http)… Cancellation Model Context Protocol · in the page specification/2025-06-18/basic/utilities/cancellation …aid theme={null} sequenceDiagram participant Client participant Server Client->>Server: Request (ID: 123) Note over Server: Processing starts Client--)Server: notifications/cancelled (… Ping Model Context Protocol · in the page specification/2025-06-18/basic/utilities/ping …ented through a simple request/response pattern. Either the client or server can initiate a ping by sending a `ping` request. ## Message Format A ping request is a standard JSON-RPC request with no… Key Changes Model Context Protocol · in the page specification/2025-06-18/changelog …2. Add support for [structured tool output](/specification/2025-06-18/server/tools#structured-content) (PR [#371](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/371)) 3. Classify… Elicitation Model Context Protocol · in the page specification/2025-06-18/client/elicitation …te> The Model Context Protocol (MCP) provides a standardized way for servers to request additional information from users through the client during interactions. This flow allows clients to maintain… Roots Model Context Protocol · in the page specification/2025-06-18/client/roots …ovides a standardized way for clients to expose filesystem "roots" to servers. Roots define the boundaries of where servers can operate within the filesystem, allowing them to understand which directo… Sampling Model Context Protocol · in the page specification/2025-06-18/client/sampling …/> The Model Context Protocol (MCP) provides a standardized way for servers to request LLM sampling ("completions" or "generations") from language models via clients. This flow allows clients to mai… Specification Model Context Protocol · in the page specification/2025-06-18/index …connections * **Clients**: Connectors within the host application * **Servers**: Services that provide context and capabilities MCP takes some inspiration from the [Language Server Protocol](https://… Schema Reference Model Context Protocol · in the page specification/2025-06-18/schema …typography"><p>Describes how important this data is for operating the server.</p> <p>A value of 1 means "most important," and indicates that the data is effectively required, while 0 means "least im… Architecture Model Context Protocol · in the page specification/2025-11-25/architecture/index …n-numbers" /> The Model Context Protocol (MCP) follows a client-host-server architecture where each host can run multiple client instances. This architecture enables users to integrate AI capabilitie… Authorization Model Context Protocol · in the page specification/2025-11-25/basic/authorization …nsport level, enabling MCP clients to make requests to restricted MCP servers on behalf of resource owners. This specification defines the authorization flow for HTTP-based transports. ### Protocol R… Overview Model Context Protocol · in the page specification/2025-11-25/basic/index …hentication and authorization framework for HTTP-based transports * **Server Features**: Resources, prompts, and tools exposed by servers * **Client Features**: Sampling and root directory lists provi… Lifecycle Model Context Protocol · in the page specification/2025-11-25/basic/lifecycle …Model Context Protocol (MCP) defines a rigorous lifecycle for client-server connections that ensures proper capability negotiation and state management. 1. **Initialization**: Capability negotiation… Transports Model Context Protocol · in the page specification/2025-11-25/basic/transports …otocol currently defines two standard transport mechanisms for client-server communication: 1. [stdio](#stdio), communication over standard in and standard out 2. [Streamable HTTP](#streamable-http)… Cancellation Model Context Protocol · in the page specification/2025-11-25/basic/utilities/cancellation …aid theme={null} sequenceDiagram participant Client participant Server Client->>Server: Request (ID: 123) Note over Server: Processing starts Client--)Server: notifications/cancelled (… Ping Model Context Protocol · in the page specification/2025-11-25/basic/utilities/ping …ented through a simple request/response pattern. Either the client or server can initiate a ping by sending a `ping` request. ## Message Format A ping request is a standard JSON-RPC request with no… Tasks Model Context Protocol · in the page specification/2025-11-25/basic/utilities/tasks …ext Protocol (MCP) allows requestors — which can be either clients or servers, depending on the direction of communication — to augment their requests with **tasks**. Tasks are durable state machines… Key Changes Model Context Protocol · in the page specification/2025-11-25/changelog …pecification/2025-06-18). ## Major changes 1. Enhance authorization server discovery with support for [OpenID Connect Discovery 1.0](https://openid.net/specs/openid-connect-discovery-1_0.html). (PR… Elicitation Model Context Protocol · in the page specification/2025-11-25/client/elicitation …/> The Model Context Protocol (MCP) provides a standardized way for servers to request additional information from users through the client during interactions. This flow allows clients to maintain… Roots Model Context Protocol · in the page specification/2025-11-25/client/roots …ovides a standardized way for clients to expose filesystem "roots" to servers. Roots define the boundaries of where servers can operate within the filesystem, allowing them to understand which directo… Sampling Model Context Protocol · in the page specification/2025-11-25/client/sampling …/> The Model Context Protocol (MCP) provides a standardized way for servers to request LLM sampling ("completions" or "generations") from language models via clients. This flow allows clients to mai… Specification Model Context Protocol · in the page specification/2025-11-25/index …connections * **Clients**: Connectors within the host application * **Servers**: Services that provide context and capabilities MCP takes some inspiration from the [Language Server Protocol](https://… Schema Reference Model Context Protocol · in the page specification/2025-11-25/schema …typography"><p>Describes how important this data is for operating the server.</p> <p>A value of 1 means "most important," and indicates that the data is effectively required, while 0 means "least im… Architecture Model Context Protocol · in the page specification/2026-07-28/architecture/index …n-numbers" /> The Model Context Protocol (MCP) follows a client-host-server architecture where each host can run multiple client instances. MCP is a stateless protocol: every request is self-containe… Client Registration Model Context Protocol · in the page specification/2026-07-28/basic/authorization/client-registration …Metadata Documents](#client-id-metadata-documents)**: When client and server have no prior relationship (most common) * **[Pre-registration](#pre-registration)**: When client and server have an existi… Authorization Model Context Protocol · in the page specification/2026-07-28/basic/authorization/index …nsport level, enabling MCP clients to make requests to restricted MCP servers on behalf of resource owners. This specification defines the authorization flow for HTTP-based transports. ### Protocol R… Authorization Security Considerations Model Context Protocol · in the page specification/2026-07-28/basic/authorization/security-considerations …nts that implementers **MUST** consider when building MCP clients and servers. Additionally, implementors **MUST** follow OAuth 2.1 security best practices as outlined in [OAuth 2.1 Section 7. "Secur… Overview Model Context Protocol · in the page specification/2026-07-28/basic/index …hentication and authorization framework for HTTP-based transports * **Server Features**: Resources, prompts, and tools exposed by servers * **Client Features**: Elicitation, sampling and root director… Cancellation Model Context Protocol · in the page specification/2026-07-28/basic/patterns/cancellation …indicate that a request it previously issued should be terminated. A server **MUST** send `notifications/cancelled` referencing a `subscriptions/listen` request ID when it tears down that subscriptio… Overview Model Context Protocol · in the page specification/2026-07-28/basic/patterns/index …ines the message patterns of the core protocol: the ways a client and server compose JSON-RPC [requests, responses, and notifications](/specification/2026-07-28/basic/index#messages) into interactions… Multi Round-Trip Requests Model Context Protocol · in the page specification/2026-07-28/basic/patterns/mrtr …e MCP specification. This replaces the previous approach of sending server-initiated requests. Servers **MUST** send server-to-client requests (such as `roots/list`, `sampling/createMessage`, or… Progress Model Context Protocol · in the page specification/2026-07-28/basic/patterns/progress …acking for long-running operations through notification messages. The server **MAY** send progress notifications to report the status of requests the client has issued. ## Progress Flow When a clien… Subscriptions Model Context Protocol · in the page specification/2026-07-28/basic/patterns/subscriptions …subscriptions/listen` opens a long-lived notification stream from the server to the client. Unlike one-off requests, the stream stays open and delivers notifications until the client cancels it. It re… Overview Model Context Protocol · in the page specification/2026-07-28/basic/transports/index …or a request-scoped SSE stream. It is also possible for clients and servers to implement [custom transports](#custom-transports). ## Messages MCP uses JSON-RPC to encode messages. JSON-RPC message… stdio Model Context Protocol · in the page specification/2026-07-28/basic/transports/stdio …-numbers" /> In the **stdio** transport, the client launches the MCP server as a subprocess. The two ends communicate over the subprocess's standard streams: * The server reads JSON-RPC messages fro… Streamable HTTP Model Context Protocol · in the page specification/2026-07-28/basic/transports/streamable-http …patibility) below. </Info> In the **Streamable HTTP** transport, the server operates as an independent process that can handle multiple client connections. At a glance: * The server exposes a single… Versioning and Compatibility Model Context Protocol · in the page specification/2026-07-28/basic/versioning …iv id="enable-section-numbers" /> This page defines how a client and server agree on what they are speaking: the protocol version, declared on every request; optional extensions, negotiated through c… Key Changes Model Context Protocol · in the page specification/2026-07-28/changelog …st`, `resources/list`, `prompts/list`) no longer vary per-connection. Servers that need cross-call state use explicit, server-minted handles passed as ordinary tool arguments ([SEP-2567](https://githu… Elicitation Model Context Protocol · in the page specification/2026-07-28/client/elicitation …/> The Model Context Protocol (MCP) provides a standardized way for servers to request additional information from users through the client during interactions. This flow allows clients to maintain… Roots Model Context Protocol · in the page specification/2026-07-28/client/roots …passing directories or files via tool parameters, resource URIs, or server configuration. See the [deprecated features registry](/specification/2026-07-28/deprecated). </Warning> The Model Contex… Sampling Model Context Protocol · in the page specification/2026-07-28/client/sampling …ng> The Model Context Protocol (MCP) provides a standardized way for servers to request LLM sampling ("completions" or "generations") from language models via clients. This flow allows clients to mai… Deprecated Features Model Context Protocol · in the page specification/2026-07-28/deprecated …8` | Pass directories or files via tool parameters, resource URIs, or server configuration | First revision released on or after 2027-07-28 | | [Sampling](/specification/2026-07-28/client/sampling) |… Specification Model Context Protocol · in the page specification/2026-07-28/index …connections * **Clients**: Connectors within the host application * **Servers**: Services that provide context and capabilities MCP takes some inspiration from the [Language Server Protocol](https://… Schema Reference Model Context Protocol · in the page specification/2026-07-28/schema …typography"><p>Describes how important this data is for operating the server.</p> <p>A value of 1 means "most important," and indicates that the data is effectively required, while 0 means "least im… Architecture Model Context Protocol · in the page specification/draft/architecture/index …n-numbers" /> The Model Context Protocol (MCP) follows a client-host-server architecture where each host can run multiple client instances. MCP is a stateless protocol: every request is self-containe… Client Registration Model Context Protocol · in the page specification/draft/basic/authorization/client-registration …Metadata Documents](#client-id-metadata-documents)**: When client and server have no prior relationship (most common) * **[Pre-registration](#pre-registration)**: When client and server have an existi…