Claude Desktop + FastMCP

Claude Desktop supports MCP servers through local STDIO connections, allowing you to extend Claude’s capabilities with custom tools, resources, and prompts from your FastMCP servers.

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Requirements

Claude Desktop requires MCP servers to run locally using STDIO transport. This means your server will communicate with Claude through standard input/output rather than HTTP.

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Create a Server

The examples in this guide will use the following simple dice-rolling server, saved as server.py.

import random
from fastmcp import FastMCP

mcp = FastMCP(name="Dice Roller")

@mcp.tool
def roll_dice(n_dice: int) -> list[int]:
    """Roll `n_dice` 6-sided dice and return the results."""
    return [random.randint(1, 6) for _ in range(n_dice)]

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

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Install the Server

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FastMCP CLI

The easiest way to install a FastMCP server in Claude Desktop is using the fastmcp install command. This automatically handles the configuration and dependency management.

fastmcp install server.py

The install command supports the same file.py:object notation as the run command. If no object is specified, it will automatically look for a FastMCP server object named mcp, server, or app in your file:

# These are equivalent if your server object is named 'mcp'
fastmcp install server.py
fastmcp install server.py:mcp

# Use explicit object name if your server has a different name
fastmcp install server.py:my_custom_server

After installation, restart Claude Desktop completely. You should see a hammer icon (🔨) in the bottom left of the input box, indicating that MCP tools are available.

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Dependencies

If your server has dependencies, include them with the --with flag:

fastmcp install server.py --with pandas --with requests

Alternatively, you can specify dependencies directly in your server code:

from fastmcp import FastMCP

mcp = FastMCP(
    name="Dice Roller",
    dependencies=["pandas", "requests"]
)

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Environment Variables

If your server needs environment variables (like API keys), you must include them:

fastmcp install server.py --name "Weather Server" \
  --env-var API_KEY=your-api-key \
  --env-var DEBUG=true

Or load them from a .env file:

fastmcp install server.py --name "Weather Server" --env-file .env

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Manual Configuration

For more control over the configuration, you can manually edit Claude Desktop’s configuration file. You can open the configuration file from Claude’s developer settings, or find it in the following locations:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

The configuration file is a JSON object with a mcpServers key, which contains the configuration for each MCP server.

{
  "mcpServers": {
    "dice-roller": {
      "command": "python",
      "args": ["path/to/your/server.py"]
    }
  }
}

After updating the configuration file, restart Claude Desktop completely. Look for the hammer icon (🔨) to confirm your server is loaded.

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Dependencies

If your server has dependencies, you can use uv or another package manager to set up the environment.

{
  "mcpServers": {
    "dice-roller": {
      "command": "uv",
      "args": [
        "run",
        "--with", "pandas",
        "--with", "requests", 
        "python",
        "path/to/your/server.py"
      ]
    }
  }
}

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Environment Variables

You can also specify environment variables in the configuration:

{
  "mcpServers": {
    "weather-server": {
      "command": "python",
      "args": ["path/to/weather_server.py"],
      "env": {
        "API_KEY": "your-api-key",
        "DEBUG": "true"
      }
    }
  }
}

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Remote Servers

Claude Desktop only supports local STDIO servers, but FastMCP can create a proxy server that forwards requests to a remote HTTP server. You can install the proxy server in Claude Desktop.

Create a proxy server that connects to a remote HTTP server:

from fastmcp import FastMCP

# Create a proxy to a remote server
proxy = FastMCP.as_proxy(
    "https://example.com/mcp/sse", 
    name="Remote Server Proxy"
)

if __name__ == "__main__":
    proxy.run()  # Runs via STDIO for Claude Desktop

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Authentication

For authenticated remote servers, create an authenticated client following the guidance in the client auth documentation and pass it to the proxy:

from fastmcp import FastMCP, Client
from fastmcp.client.auth import BearerAuth

# Create authenticated client
client = Client(
    "https://api.example.com/mcp/sse",
    auth=BearerAuth(token="your-access-token")
)

# Create proxy using the authenticated client
proxy = FastMCP.as_proxy(client, name="Authenticated Proxy")

if __name__ == "__main__":
    proxy.run()