mirror of https://github.com/PrefectHQ/fastmcp.git synced 2026-08-09 15:19:10 +02:00

Jeremiah Lowin 7339936980

Rewrite the v4 What's New page and document server extensions (#4698 )

* Rewrite the v4 What's New page

Teach the headline features with code instead of asserting them, drop the
major-version throat-clearing and SEP list, and correct the elicitation
claim: ctx.elicit() is unchanged and handshake-only, while sampling and
roots are removed outright.

* Fix broken doc links and stale version references

Repoint five dead links and anchors, refresh v3-era version examples on the
v4 docs, and add the missing FastMCP 3 entry to the installation page's
upgrade section.

* Document server extensions

add_extension() shipped in v4 with no documentation page. Covers the
extension interface, request methods, tool-call interception, lifespan
ownership, and the client half.

* Link the FastMCP TypeScript library

* Address Codex review feedback

Gate the extension interceptor on the client's per-request opt-in rather
than claiming negotiation does it; show the v4 beta pin on the install
page instead of a version a reader cannot get; note that UserSession
requires authentication.

2026-07-28 20:05:45 -04:00

7.4 KiB

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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.

Building in TypeScript? FastMCP for TypeScript is the official counterpart, built and maintained by the same team. Same pillars, same ideas, npm install @prefecthq/fastmcp-ts.

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 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.

7.4 KiB Raw Blame History