- Python 100%
7184a4ca21* OTEL: Fix attribute compliance and improve telemetry helpers
Attribute compliance:
- Remove rpc.system/service/method (MCP is not traditional RPC)
- Add gen_ai.tool.name on tools/call spans
- Add gen_ai.prompt.name on prompts/get spans
- Fix session_id check (truthy -> is not None)
Telemetry helper improvements:
- Add is_recording() guards to skip work on non-recording spans
- Add error.type attribute with __qualname__ on error spans
- Use isinstance check for ToolError to set "tool_error" error type
- Include exception message in span status description
- Add tool_name/prompt_name params to server_span and client_span
Client call_tool enrichment:
- Reflect tool-level errors (result.isError) on client span status
so callers see ERROR even though the MCP protocol call succeeded
🤖 Generated with Claude Code
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* fix: remove resource URI from span names to avoid high-cardinality
Per MCP semantic conventions, resource URIs SHOULD NOT be included in
span names by default since they can be unbounded (especially with
templates like users://{id}/profile). The URI remains available via
the mcp.resource.uri attribute.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* fix: add missing gen_ai/mcp attributes to proxy and delegate spans
- Proxy tool spans: add gen_ai.tool.name
- Proxy prompt spans: add gen_ai.prompt.name
- All delegate spans: add mcp.method.name
- Docs: remove rpc.* references, update span names and attributes table
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* Hoist ToolError imports to module level, add rpc.* migration note
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---------
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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| tests | ||
| v3-notes | ||
| .ccignore | ||
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| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
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| LICENSE | ||
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| 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.