585 pages for host.

Architecture overview Model Context Protocol · in the page docs/draft/learn/architecture …# Participants MCP follows a client-server architecture where an MCP host — an AI application like [Claude Code](https://www.anthropic.com/claude-code) or [Claude Desktop](https://www.claude.ai/downl… Understanding MCP clients Model Context Protocol · in the page docs/draft/learn/client-concepts # Understanding MCP clients MCP clients are instantiated by host applications to communicate with particular MCP servers. The host application, like Claude.ai or an IDE, manages the overall user expe… Debugging Model Context Protocol · in the page docs/draft/tools/debugging …ll messages logged to stderr (standard error) will be captured by the host application automatically. <Warning> Local MCP servers should not log messages to stdout (standard out), as this will in… MCP Inspector Model Context Protocol · in the page docs/draft/tools/inspector …Importing client configs, reviewing MCP Apps, Docker, and network hosting. </Card> <Card title="Debugging guide" icon="bug" href="/docs/draft/tools/debugging"> Broader debugging strategie… Authorization Model Context Protocol · in the page docs/draft/tools/inspector/authorization …ace | Default callback | Why | | - | - | - | | **Web** | `http://localhost:6274/oauth/callback` | The main app server already has an HTTP listener. | | **CLI** | `http://127.0.0.1:6276/oauth/callback`… CLI client Model Context Protocol · in the page docs/draft/tools/inspector/cli …oopback OAuth flow as the TUI: it opens a browser and waits on a localhost callback that a CI job can't complete. Two flags make non-interactive runs predictable: * `--stored-auth-only`: never start… Configuration and flags Model Context Protocol · in the page docs/draft/tools/inspector/configuration …r. Default `http://127.0.0.1:6276/oauth/callback`. Must be a loopback host (`127.0.0.1` or `localhost`): the local callback listener receives the authorization code over plaintext `http`, so any other… Recipes Model Context Protocol · in the page docs/draft/tools/inspector/recipes …ransports, importing configs, reviewing MCP Apps, Docker, and network hosting ## Connecting stdio vs. HTTP servers ### stdio A stdio server is a process the Inspector spawns. Everything positional… TUI client Model Context Protocol · in the page docs/draft/tools/inspector/tui …f tools, resources, and prompts as the web client. Use it on a remote host over SSH, in a locked-down environment, or when you prefer to stay in the terminal. ```bash theme={null} npx @modelcontextpr… Web client Model Context Protocol · in the page docs/draft/tools/inspector/web …a URL containing that token: **open that URL**, and don't type `localhost:6274` from memory. The browser recovers the token from three places, in priority order: 1. `window.__INSPECTOR_API_TOKEN__`… Understanding Authorization in MCP Model Context Protocol · in the page docs/draft/tutorials/security/authorization …e designed for HTTP-based transports where the MCP server is remotely-hosted and the client uses OAuth to establish that a user is authorized to access said remote server. </Tip> ## The Authorization… Security Best Practices Model Context Protocol · in the page docs/draft/tutorials/security/security_best_practices …If using cookies to track consent decisions, they **MUST**: * Use `__Host-` prefix for cookie names * Set `Secure`, `HttpOnly`, and `SameSite=Lax` attributes * Be cryptographically signed or use serv… Build an MCP App Model Context Protocol · in the page extensions/apps/build …g tools and resources) and the client side (the `App` class for UI-to-host communication). Vite with the `vite-plugin-singlefile` plugin is used here to bundle your UI and assets into a single HTML fi… MCP Apps Model Context Protocol · in the page extensions/apps/overview # MCP Apps > Interactive UI applications that render inside MCP hosts like Claude Desktop <Tip> For comprehensive API documentation, advanced patterns, and the full specification, visit the [offic… Skills Model Context Protocol · in the page extensions/skills/overview …nity/working-groups/skills-over-mcp) maintains the extension. SDK and host support is still being implemented; see the [client support matrix](/extensions/client-matrix) and [implementations list](htt… Tasks Model Context Protocol · in the page extensions/tasks/overview …an extension to the [core MCP specification](/specification/latest). Host support varies by client. </Note> See the [client matrix](/extensions/client-matrix) for extension support across clients.… The MCP Registry Model Context Protocol · in the page registry/about …Registries Package registries — such as npm, PyPI, and Docker Hub — host packages with code and binaries. The MCP Registry hosts metadata that points to those packages. For example, a `weather-mcp… How to Authenticate When Publishing to the Official MCP Registry Model Context Protocol · in the page registry/authentication …ication method that relies on a `/.well-known/mcp-registry-auth` file hosted on your domain. For example, `https://example.com/.well-known/mcp-registry-auth`. To perform HTTP authentication using the… MCP Registry Supported Package Types Model Context Protocol · in the page registry/package-types …For MCPB packages, the MCP Registry currently supports MCPB artifacts hosted via GitHub or GitLab releases. MCPB packages use `"registryType": "mcpb"` in `server.json`. For example: ```json server.j… Quickstart: Publish an MCP Server to the MCP Registry Model Context Protocol · in the page registry/quickstart …r is written in TypeScript. * **npm account** — The MCP Registry only hosts metadata, not artifacts. Before publishing to the MCP Registry, we will publish the MCP server's package to npm, so you will… MCP Registry Aggregators Model Context Protocol · in the page registry/registry-aggregators …i.yaml) defined by the MCP Registry. This allows clients, such as MCP host applications, to consume server metadata via a standardized interface. The subregistry OpenAPI spec allows subregistries to… Publishing Remote Servers Model Context Protocol · in the page registry/remote-servers …t with the `packages` property in `server.json` in order to allow MCP host applications to choose the preferred method of installation. ```json server.json highlight={7-22} theme={null} { "$schema"… Official MCP Registry Terms of Service Model Context Protocol · in the page registry/terms-of-service …vern your access to and use of the official MCP Registry (the service hosted at [https://registry.modelcontextprotocol.io/](https://registry.modelcontextprotocol.io/) or a successor location) (“Regist… SEP-1302: Formalize Working Groups and Interest Groups in MCP Governance Model Context Protocol · in the page seps/1302-formalize-working-groups-and-interest-groups-in-mc …, mostly in pursuit of creating artifacts for SEP consideration (e.g. hosting, UI, tool-interfaces, search-tools) With SEP-994 resulting in the merging of the Discord communities, we have a need to:… SEP-1686: Tasks Model Context Protocol · in the page seps/1686-tasks …ken to integrate with MCP’s progress-tracking functionality, enabling host applications to receive status updates for a tool call via notifications. However, there is no way for a client to explicitly… SEP-1865: MCP Apps - Interactive User Interfaces for MCP Model Context Protocol · in the page seps/1865-mcp-apps-interactive-user-interfaces-for-mcp …-1724) that enables servers to deliver interactive user interfaces to hosts. MCP Apps introduces a standardized pattern for declaring UI resources via the `ui://` URI scheme, associating them with too… SEP-2106: Tools `inputSchema` & `outputSchema` Conform to JSON Schema 2020-12 Model Context Protocol · in the page seps/2106-json-schema-2020-12 …ch amplification primitive: a malicious tool definition can cause the host to fetch arbitrary URLs, including internal metadata endpoints or large payloads designed to exhaust resources. To mitigate… SEP-2322: Multi Round-Trip Requests Model Context Protocol · in the page seps/2322-MRTR …istRoots is very low or blocked for many Remote MCP servers or Server Hosted Clients due to the operational complextity of supporting the SSE streams and server-side state. ## Motivation Note: This… SEP-2468: Recommend Issuer (iss) Parameter in MCP Auth Responses Model Context Protocol · in the page seps/2468-recommend-issuer-claim-for-auth …ive on the wire. Client validation introduces a behavioral change for hosts whose authorization server advertises `authorization_response_iss_parameter_supported: true` but whose callback handling doe… SEP-2567: Sessionless MCP via Explicit State Handles Model Context Protocol · in the page seps/2567-sessionless-mcp …does not say when a session begins or ends, because it depends on the host application. In practice, deployed clients vary widely and few scope sessions to a conversation: ChatGPT creates a fresh sess… SEP-2640: Skills Extension Model Context Protocol · in the page seps/2640-skills-extension …kills.io/specification#progressive-disclosure) model that governs how hosts stage content into context) is delegated entirely to the [Agent Skills specification](https://agentskills.io/specification);… SEP-2663: Tasks Extension Model Context Protocol · in the page seps/2663-tasks-extension …lementation challenges, tasks face another structural issue: **Client-hosted tasks are no longer expressible.** [SEP-1686](./1686-tasks.md) permitted clients to host tasks for elicitation and sampling… SEP-991: Enable URL-based Client Registration using OAuth Client ID Metadata Documents Model Context Protocol · in the page seps/991-enable-url-based-client-registration-using-oauth-c …t clients they've never seen before** based on: * The HTTPS domain hosting the metadata * The metadata content itself * Domain reputation and security policies 2. **Servers maintain full con… Architecture Model Context Protocol · in the page specification/2024-11-05/architecture/index # Architecture 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 capabiliti… Transports Model Context Protocol · in the page specification/2024-11-05/basic/transports …attacks 2. When running locally, servers **SHOULD** bind only to localhost (127.0.0.1) rather than all network interfaces (0.0.0.0) 3. Servers **SHOULD** implement proper authentication for all connec… Specification Model Context Protocol · in the page specification/2024-11-05/index …w.jsonrpc.org/) 2.0 messages to establish communication between: * **Hosts**: LLM applications that initiate connections * **Clients**: Connectors within the host application * **Servers**: Services… Resources Model Context Protocol · in the page specification/2024-11-05/server/resources …del Resources in MCP are designed to be **application-driven**, with host applications determining how to incorporate context based on their needs. For example, applications could: * Expose resourc… Logging Model Context Protocol · in the page specification/2024-11-05/server/utilities/logging …a": { "error": "Connection failed", "details": { "host": "localhost", "port": 5432 } } } } ``` ## Message Flow ```mermaid theme={null} sequenceDiagram par… Architecture Model Context Protocol · in the page specification/2025-03-26/architecture/index # Architecture 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 capabiliti… Authorization Model Context Protocol · in the page specification/2025-03-26/basic/authorization …on endpoints are consistently located at the root level of the domain hosting the MCP server, regardless of any path components in the MCP server URL. #### Fallbacks for Servers without Metadata Disc… Transports Model Context Protocol · in the page specification/2025-03-26/basic/transports …attacks 2. When running locally, servers **SHOULD** bind only to localhost (127.0.0.1) rather than all network interfaces (0.0.0.0) 3. Servers **SHOULD** implement proper authentication for all connec… Specification Model Context Protocol · in the page specification/2025-03-26/index …w.jsonrpc.org/) 2.0 messages to establish communication between: * **Hosts**: LLM applications that initiate connections * **Clients**: Connectors within the host application * **Servers**: Services… Resources Model Context Protocol · in the page specification/2025-03-26/server/resources …del Resources in MCP are designed to be **application-driven**, with host applications determining how to incorporate context based on their needs. For example, applications could: * Expose resourc… Logging Model Context Protocol · in the page specification/2025-03-26/server/utilities/logging …a": { "error": "Connection failed", "details": { "host": "localhost", "port": 5432 } } } } ``` ## Message Flow ```mermaid theme={null} sequenceDiagram par… Architecture Model Context Protocol · in the page specification/2025-06-18/architecture/index …ection-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 capabi… Authorization Model Context Protocol · in the page specification/2025-06-18/basic/authorization …rization server are beyond the scope of this specification. It may be hosted with the resource server or a separate entity. The [Authorization Server Discovery section](#authorization-server-discovery… Transports Model Context Protocol · in the page specification/2025-06-18/basic/transports …attacks 2. When running locally, servers **SHOULD** bind only to localhost (127.0.0.1) rather than all network interfaces (0.0.0.0) 3. Servers **SHOULD** implement proper authentication for all connec… Specification Model Context Protocol · in the page specification/2025-06-18/index …w.jsonrpc.org/) 2.0 messages to establish communication between: * **Hosts**: LLM applications that initiate connections * **Clients**: Connectors within the host application * **Servers**: Services… Schema Reference Model Context Protocol · in the page specification/2025-06-18/schema …4 encoding or any tokenization), if known.</p> <p>This can be used by Hosts to display file sizes and estimate context window usage.</p> </div><aside class="tsd-sources"> <p>Inherited from <a href="#r… Resources Model Context Protocol · in the page specification/2025-06-18/server/resources …del Resources in MCP are designed to be **application-driven**, with host applications determining how to incorporate context based on their needs. For example, applications could: * Expose resourc…