fastmcp

# FastMCP - Build MCP Servers in Python

FastMCP is a Python framework for building Model Context Protocol (MCP) servers that expose tools, resources, and prompts to Large Language Models like Claude.

## Quick Start

### Installation

```bash
pip install fastmcp
# or: uv pip install fastmcp
```

### Minimal Server

```python
from fastmcp import FastMCP

# MUST be at module level for FastMCP Cloud
mcp = FastMCP("My Server")

@mcp.tool()
async def hello(name: str) -> str:
    """Say hello to someone."""
    return f"Hello, {name}!"

if __name__ == "__main__":
    mcp.run()
```

**Run:**
```bash
python server.py              # Local development
fastmcp dev server.py         # With FastMCP CLI
python server.py --transport http --port 8000  # HTTP mode
```

**Copy-Paste Template**: See `templates/basic-server.py`

## Core Concepts

### Tools

Functions that LLMs can call:

```python
@mcp.tool()
def calculate(operation: str, a: float, b: float) -> float:
    """Perform mathematical operations."""
    operations = {
        "add": lambda x, y: x + y,
        "subtract": lambda x, y: x - y,
        "multiply": lambda x, y: x * y,
        "divide": lambda x, y: x / y if y != 0 else None
    }
    return operations.get(operation, lambda x, y: None)(a, b)
```

**Best Practices:**
- Clear, descriptive function names
- Comprehensive docstrings (LLMs read these!)
- Strong type hints (Pydantic validates automatically)
- Return structured data (dicts/lists)
- Handle errors gracefully

### Resources

Expose static or dynamic data:

```python
@mcp.resource("data://config")
def get_config() -> dict:
    """Provide application configuration."""
    return {"version": "1.0.0", "features": ["auth", "api"]}

# Dynamic resource with parameters
@mcp.resource("user://{user_id}/profile")
async def get_user_profile(user_id: str) -> dict:
    """Get user profile by ID."""
    return {"id": user_id, "name": f"User {user_id}"}
```

**URI Schemes**: `data://`, `file://`, `resource://`, `info://`,