fastmcp 3.4.2

The fast, Pythonic way to build MCP servers and clients.

FastMCP 🚀

Move fast and make things.

Made with 💙 by Prefect

---

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:

• Upgrading from FastMCP v2
• Upgrading from the MCP Python SDK
• Upgrading from the low-level SDK

[!NOTE] If import fastmcp fails right after a pip upgrade from FastMCP 3.2 or earlier, run pip install --force-reinstall fastmcp. See Troubleshooting for why this happens (uv is 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.txt is essentially a sitemap, listing all the pages in the documentation.
• llms-full.txt contains 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.