- Python 100%
8363ec4d26* Design doc: stateless session state * Add stateless session-state primitives: Scope, SessionCodec, scoped state * Add SessionProvider and Session() annotation for stateless session state * Rewrite session-state design to final shape (Session object, two patterns, no seal) * Rework stateless session state to final Session/SessionId design Remove Scope, SessionCodec/sealing, and scoped ctx.get_state. Add the Session object (get/set/delete/clear over one dict per (principal, session_id) key), injected session: Session (keyed by principal, requires auth), session_id: SessionId argument with auto-filled description, and SessionProvider contributing create_session/end_session. * Rename injected marker to UserSession; auto-wire SessionProvider on SessionId * Document stateless session state as a v4 feature * Require SessionProvider and make sessions create-then-validate Remove the implicit SessionProvider auto-wiring; a SessionProvider must now be registered explicitly. create_session records an owned session and get_session validates the id, rejecting uncreated or foreign ids. * Add Session.id (public id for session_id sessions, None for UserSession) * Fix ty: narrow Tool | None and ToolResult.structured_content in session tests * Fix session-provider enforcement gap for non-local tools; stop embedding raw principal in UserSession key * Fix disabled session_id tools blocking listing; reject local tools shadowing SessionProvider lifecycle names * Decouple SessionId description from lifecycle tool name so it survives namespaced mounts * Remove SessionProvider enforcement; get_session validation is the guarantee * Fix stale enforcement/key-format docs; document store-owned session TTL * Dedup SessionId contract description; tighten context.mdx session-state lead * Make session store/description resolution work in Docket task workers and for partial tools * Expose get_session as a standalone task-safe function; drop foreground-only Context.get_session * Move get_session to dependencies alongside the other request accessors * Reframe context state docs as Request State; cross-request persistence points to Session State * Address UserSession injection edge cases from review - inject a UserSession instance (not bare Session) so isinstance holds - support session: UserSession | None = None (inject None when unauth) - detect SessionId params past a partial's positional binding |
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| skills/fastmcp-client-cli | ||
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| v3-notes | ||
| .ccignore | ||
| .coderabbit.yaml | ||
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| AGENTS.md | ||
| CLAUDE.md | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| justfile | ||
| LICENSE | ||
| logo.py | ||
| loq.toml | ||
| pyproject.toml | ||
| README.md | ||
| SECURITY.md | ||
| uv.lock | ||
The Model Context Protocol (MCP) connects LLMs to tools and data. FastMCP gives you everything you need to go from prototype to production:
from fastmcp import FastMCP
mcp = FastMCP("Demo 🚀")
@mcp.tool
def add(a: int, b: int) -> int:
"""Add two numbers"""
return a + b
if __name__ == "__main__":
mcp.run()
Why FastMCP
Building an effective MCP application is harder than it looks. FastMCP handles all of it. Declare a tool with a Python function, and the schema, validation, and documentation are generated automatically. Connect to a server with a URL, and transport negotiation, authentication, and protocol lifecycle are managed for you. You focus on your logic, and the MCP part just works: with FastMCP, best practices are built in.
That's why FastMCP is the standard framework for working with MCP. FastMCP 1.0 was incorporated into the official MCP Python SDK in 2024. Today, the actively maintained standalone project is downloaded a million times a day, and some version of FastMCP powers 70% of MCP servers across all languages.
FastMCP has three pillars:
Servers Expose tools, resources, and prompts to LLMs. |
Apps Give your tools interactive UIs rendered directly in the conversation. |
Clients Connect to any MCP server — local or remote, programmatic or CLI. |
Servers wrap your Python functions into MCP-compliant tools, resources, and prompts. Clients connect to any server with full protocol support. And Apps give your tools interactive UIs rendered directly in the conversation.
Ready to build? Start with the installation guide or jump straight to the quickstart.
Run FastMCP in production with Horizon
FastMCP is the standard way to build MCP servers. Prefect Horizon is the enterprise MCP gateway for running them safely.
Built by the FastMCP team, Horizon packages the best practices we've learned shipping the world's most popular MCP framework.
Deploy FastMCP servers from GitHub with branch previews and instant rollback. Create a private registry of every MCP your company uses. Secure access with SSO and tool-level RBAC. Get audit logs, observability, and governance across your MCP stack. Remix approved tools into purpose-built endpoints for teams and agents.
Start with FastMCP. Scale with Horizon →
Installation
We recommend installing FastMCP with uv:
uv pip install fastmcp
For full installation instructions, including verification and upgrading, see the Installation Guide.
Upgrading? We have guides for:
Note
If
import fastmcpfails right after apipupgrade from FastMCP 3.2 or earlier, runpip install --force-reinstall fastmcp. See Troubleshooting for why this happens (uvis unaffected).
📚 Documentation
FastMCP's complete documentation is available at gofastmcp.com, including detailed guides, API references, and advanced patterns.
Documentation is also available in llms.txt format, which is a simple markdown standard that LLMs can consume easily:
llms.txtis essentially a sitemap, listing all the pages in the documentation.llms-full.txtcontains the entire documentation. Note this may exceed the context window of your LLM.
Community: Join our Discord server to connect with other FastMCP developers and share what you're building.
Contributing
We welcome contributions! See the Contributing Guide for setup instructions, testing requirements, and PR guidelines.