# FastMCP

> **Note**: This is experimental software. The Model Context Protocol itself is only a few days old and the specification is still evolving.

A fast, pythonic way to build Model Context Protocol (MCP) servers.

The Model Context Protocol is an extremely powerful way to give LLMs access to tools and resources. However, building MCP servers can be difficult and cumbersome. FastMCP provides a simple, intuitive interface for creating MCP servers in Python.

## Installation

MCP servers require you to use [uv](https://github.com/astral-sh/uv) as your dependency manager.


Install uv with brew:
```bash
brew install uv
```
*(Editor's note: I was unable to get MCP servers working unless uv was installed with brew.)*

Install FastMCP:
```bash
uv pip install fastmcp
```



## Quick Start

Here's a simple example that exposes your desktop directory as a resource and provides a basic addition tool:

```python
from pathlib import Path
from fastmcp import FastMCP

# Create server
mcp = FastMCP("Demo")

@mcp.resource("dir://desktop")
def desktop() -> list[str]:
    """List the files in the user's desktop"""
    desktop = Path.home() / "Desktop"
    return [str(f) for f in desktop.iterdir()]

@mcp.tool()
def add(a: int, b: int) -> int:
    """Add two numbers"""
    return a + b

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

## Features

### Resources

Resources are data sources that can be accessed by the LLM. They can be files, directories, or any other data source. Resources are defined using the `@resource` decorator:

```python
@mcp.resource("file://config.json")
def get_config() -> str:
    """Read the config file"""
    return Path("config.json").read_text()
```

### Tools

Tools are functions that can be called by the LLM. They are defined using the `@tool` decorator:

```python
@mcp.tool()
def calculate(x: int, y: int) -> int:
    """Perform a calculation"""
    return x + y
```

## Development

### Running the Dev Inspector

FastMCP includes a development server with the MCP Inspector for testing your server:

```bash
# Basic usage
fastmcp dev your_server.py

# Install package in editable mode from current directory
fastmcp dev your_server.py --with-editable .

# Install additional packages
fastmcp dev your_server.py --with pandas --with numpy

# Combine both
fastmcp dev your_server.py --with-editable . --with pandas --with numpy
```

The `--with` flag automatically includes `fastmcp` and any additional packages you specify. The `--with-editable` flag installs the package from the specified directory in editable mode, which is useful during development.

### Installing in Claude

To use your server with Claude Desktop:

```bash
# Basic usage
fastmcp install your_server.py --name "My Server"

# Install package in editable mode
fastmcp install your_server.py --with-editable .

# Install additional packages
fastmcp install your_server.py --with pandas --with numpy

# Combine options
fastmcp install your_server.py --with-editable . --with pandas --with numpy
```


## Configuration

FastMCP can be configured via environment variables with the prefix `FASTMCP_`:

- `FASTMCP_DEBUG`: Enable debug mode
- `FASTMCP_LOG_LEVEL`: Set logging level (DEBUG, INFO, WARNING, ERROR, CRITICAL)
- `FASTMCP_HOST`: HTTP server host (default: 0.0.0.0)
- `FASTMCP_PORT`: HTTP server port (default: 8000)

## License

Apache 2.0