- Python 100%
0cf31e1893* fix: resolve OpenAPI 3.x server variables in _create_default_client When an OpenAPI spec defines server variables (e.g. `https://{region}.api.example.com/v1`), the default values are now substituted before constructing the httpx client base URL. Previously, the URL was used as-is, causing all requests to fail for specs that use server variable templating. Fixes #1681 * fix: use str.replace instead of format_map for server variable substitution format_map applies Python string formatting rules, so variable names like {api.version} would be treated as attribute access and raise errors. Literal token replacement handles all valid OpenAPI variable names safely. * fix: task.wait() now returns on input_required instead of hanging Previously, wait() used a terminal-state allowlist (completed, failed, cancelled), so tasks entering input_required would hang until timeout. Replaced with inverse logic: return whenever the task exits the 'working' state. This handles input_required and any future blocking states without needing to update the allowlist. Fixes #3779 * fix: include submitted in in_progress_states to avoid premature return * fix: revert submitted, update state docstring to match MCP spec * fix: add _wait_terminal() so result() waits for completed/failed/cancelled wait() correctly returns on input_required for human-in-the-loop use cases, but result() needs to wait until the task fully resolves. Add a private _wait_terminal() helper that loops through non-terminal states and use it in all result() implementations. |
||
|---|---|---|
| .claude | ||
| .cursor/rules | ||
| .github | ||
| docs | ||
| examples | ||
| scripts | ||
| skills/fastmcp-client-cli | ||
| src/fastmcp | ||
| 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. When you're ready to deploy, Prefect Horizon offers free hosting for FastMCP users.
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:
📚 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.