- Python 100%
bcf90d5ae7Most pins in tests/server/providers/proxy/ were added only to keep tests green while unpinning changed which protocol era the proxy's backend connection used, not because the test's subject cared about the era. With proxy era-mirroring (#4573) landed, a front client on auto correctly moves the whole chain to the modern protocol, so plain tool/resource/prompt calls through a proxy no longer need a pin. Kept pins fall into three buckets, each commented at the call site: tests whose subject is genuinely handshake-only (sampling, roots, elicitation push-forwarding, ping, initialize handshake mechanics); tests whose backend is a directly-constructed ProxyClient/StatefulProxyClient, which always defaults to legacy independent of the front era; and two tests left pinned with a TODO documenting a real defect this audit surfaced (upstream instructions not forwarded to a modern-era client through a proxy, and ProxyProvider.list_tools leaking an unwrapped connection error instead of an MCPError). |
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| .claude | ||
| .cursor/rules | ||
| .github | ||
| docs | ||
| examples | ||
| fastmcp_remote | ||
| fastmcp_slim | ||
| scripts | ||
| skills/fastmcp-client-cli | ||
| tests | ||
| v3-notes | ||
| .ccignore | ||
| .coderabbit.yaml | ||
| .gitignore | ||
| .pre-commit-config.yaml | ||
| .python-version | ||
| 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.