PyMCP Kit¶

An opinionated implementation of the Model Context Protocol for FastAPI. The spec leaves room for many designs; pymcp-kit picks one: a small built-in transport surface, app-scoped registries, and the MCP features you typically need first: tools, prompts, resources, roots, task-aware execution, optional auth hooks, OAuth protected-resource metadata, and opt-in draft MCP support.

Get Started Runtime Surface

Small transport surface¶

Use Streamable HTTP at /mcp for networked clients and stdio for subprocess-based MCP hosts.

App-scoped registries¶

Register tools, prompts, and resources globally for simple setups, then let create_app() snapshot them into an isolated app runtime.

Tasks that stay useful¶

Opt tools into task execution, emit progress, request user input, support cancellation, and return results without flattening structured payloads.

Security when you need it¶

Add bearer-token authentication, rule-based authorization, token introspection, and OAuth protected-resource metadata without turning the package into a large framework.

Spec conformant¶

Passes the official MCP conformance suite in full against the 2025-11-25 spec, verified in CI on every change.

Opinionated by design¶

PyMCP Kit follows the MCP specification, and makes the choices the spec leaves open:

Two transports, nothing more. Streamable HTTP at /mcp for networked clients and stdio for subprocess hosts.
Registries are app-scoped. Register tools, prompts, and resources globally, and create_app() snapshots them into an isolated runtime.
Stable by default, draft by opt-in. Stable MCP revisions are served by default; the draft 2026-07-28 stateless flow is something you enable.
Security is a hook, not a framework. Authentication, authorization, and OAuth protected-resource metadata are optional hooks you add when you need them.
Conformance is checked, not claimed. The official MCP conformance suite runs in CI on every change.

Quick Install¶

pip install pymcp-kit

How It Fits Together¶

create_app() snapshots the registries into an isolated runtime, mounts the Streamable HTTP transport at /mcp, and routes every request through the same dispatch pipeline that the stdio transport uses:

flowchart LR
    C1[MCP client] -->|Streamable HTTP /mcp| T[Transport layer]
    C2[MCP host] -->|stdio| T
    T --> SM[Session manager]
    T --> D[Dispatcher]
    D --> G[Middleware gates<br/>error boundary, init,<br/>capability, authorization]
    G --> H[Method handlers<br/>tools, prompts, resources,<br/>roots, tasks]
    H --> R[App-scoped registries]
    H --> E[Task engine]
    SEC[Security hooks<br/>authn, authz,<br/>OAuth metadata] -.-> T
    SEC -.-> D

What Ships Today¶

Streamable HTTP mounted at /mcp
Stdio transport through run_stdio_server(app)
Stable MCP revisions by default, with opt-in draft 2026-07-28 stateless support
Tool, prompt, and resource registries
Roots and resource subscriptions
Task-aware tool execution with progress, cancellation, and elicitation
Optional authentication, authorization, and OAuth protected-resource metadata hooks

Main Protocol Surface¶

Lifecycle: initialize, ping, notifications/initialized, notifications/cancelled
Tools: tools/list, tools/call
Prompts: prompts/list, prompts/get
Resources: resources/list, resources/read, resources/subscribe, resources/unsubscribe
Roots: roots/list
Tasks: tasks/list, tasks/get, tasks/cancel, tasks/result
Draft discovery: server/discover when draft mode is enabled