fastmcp-slim
The dependency-slim FastMCP package.
Decision gist · record as of 2026-08-14
Yes. FastMCP-slim is actively maintained, has no known vulnerabilities, low install friction, and is the de facto standard for building MCP servers in Python. Install it if you need to expose Python functions to LLMs or integrate with MCP-compatible tools. The permissive Apache license and broad Python version support (3.10–3.13) make it suitable for both prototypes and production use.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.10 or later.
- Low friction install with six common runtime dependencies.
- Actively maintained with a release 4 days old; the project is at top_1000 popularity tier with 27207 repository stars and no known security vulnerabilities.
License · maintenance · safety
Apache-2.0 (permissive) — Apache-2.0 permissive license allows commercial and private use with minimal restrictions.
last release 2026-08-10 (4 days) · last repo commit 2026-08-14 · 27,207 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 81,942,649 downloads/mo, #409 on PyPI
Alternatives
Verify before relying
pip install fastmcp-slim
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()- Whether fastmcp-slim is a true slim variant with reduced dependencies compared to the full fastmcp package.
- Performance characteristics and latency overhead of the MCP protocol layer.
- Compatibility with specific LLM platforms beyond the generic MCP standard.
What it is and what it does
FastMCP is a Python framework that wraps your functions into Model Context Protocol (MCP) servers, allowing LLMs to discover and call them as tools. It handles schema generation, validation, authentication, and protocol lifecycle automatically—you write a Python function, decorate it with @mcp.tool, and FastMCP exposes it as an MCP-compliant endpoint. The framework supports three modes: servers (expose tools to LLMs), clients (connect to any MCP server), and apps (render interactive UIs in conversations).
The package depends on pydantic for validation, python-dotenv for configuration, rich for terminal output, platformdirs for file paths, and typing-extensions for type hints. It targets modern Python versions (3.10–3.13) and is actively maintained by Prefect, the team behind the official MCP Python SDK. FastMCP is widely adopted—the fact sheet notes it powers 70% of MCP servers across all languages and receives a million downloads per day.
Use it for
- Build an MCP server that exposes your Python utilities as tools for Claude or other LLMs to call.
- Connect your application to remote MCP servers to integrate third-party tools and data sources.
- Create interactive agent tools with UI components rendered directly in LLM conversations.
- Prototype and deploy LLM-integrated applications without manually writing MCP protocol code.
- Migrate from the low-level MCP SDK or older FastMCP versions to a modern, maintained framework.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
FastMCP-slim is actively maintained, has no known vulnerabilities, low install friction, and is the de facto standard for building MCP servers in Python. Install it if you need to expose Python functions to LLMs or integrate with MCP-compatible tools. The permissive Apache license and broad Python version support (3.10–3.13) make it suitable for both prototypes and production use.
Install
fastmcp-slim on PyPI
Before you install
Low friction install with six common runtime dependencies. Actively maintained with a release 4 days old; the project is at top_1000 popularity tier with 27207 repository stars and no known security vulnerabilities.
Requires Python 3.10 or later.
License in practice
Apache-2.0 permissive license allows commercial and private use with minimal restrictions.
Quickstart
pip install fastmcp-slim
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()Verify before relying
- Whether fastmcp-slim is a true slim variant with reduced dependencies compared to the full fastmcp package.
- Performance characteristics and latency overhead of the MCP protocol layer.
- Compatibility with specific LLM platforms beyond the generic MCP standard.
Package facts
| License | Apache-2.0 permissive |
| Python support | Supports the current Python release >=3.10 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | 6 packagesplatformdirspydantic-settingspydanticpython-dotenvrichtyping-extensions |
| Maintenance | Actively maintained 4 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 81,942,649 / month, #409 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Intended Audience :: DevelopersLicense :: OSI Approved :: Apache Software LicenseProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Topic :: Scientific/Engineering :: Artificial IntelligenceTyping :: Typed |
Evidence: fastmcp_slim-3.4.7-py3-none-any.whl
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