FastMCP CLI

import { VersionBadge } from "/snippets/version-badge.mdx"

FastMCP provides a command-line interface (CLI) that makes it easy to run, develop, and install your MCP servers. The CLI is automatically installed when you install FastMCP.

fastmcp --help

Commands Overview

fastmcp run

Run a FastMCP server directly or proxy a remote server.

fastmcp run server.py

Options

Entrypoints

The fastmcp run command supports the following entrypoints:

1. Inferred server instance: server.py - imports the module and looks for a FastMCP server instance named mcp, server, or app. Errors if no such object is found.
2. Explicit server entrypoint: server.py:custom_name - imports and uses the specified server entrypoint
3. Factory function: server.py:create_server - calls the specified function (sync or async) to create a server instance
4. Remote server proxy: https://example.com/mcp-server - connects to a remote server and creates a local proxy server
5. FastMCP configuration file: fastmcp.json - runs servers using FastMCP's declarative configuration format (auto-detects files in current directory)
6. MCP configuration file: mcp.json - runs servers defined in a standard MCP configuration file

If you need setup code to run, use the factory pattern instead. </Warning>

Inferred Server Instance

If you provide a path to a file, fastmcp run will load the file and look for a FastMCP server instance stored as a variable named mcp, server, or app. If no such object is found, it will raise an error.

For example, if you have a file called server.py with the following content:

from fastmcp import FastMCP

mcp = FastMCP("MyServer")

You can run it with:

fastmcp run server.py

Explicit Server Entrypoint

If your server is stored as a variable with a custom name, or you want to be explicit about which server to run, you can use the following syntax to load a specific server entrypoint:

fastmcp run server.py:custom_name

For example, if you have a file called server.py with the following content:

from fastmcp import FastMCP

my_server = FastMCP("CustomServer")

@my_server.tool
def hello() -> str:
    return "Hello from custom server!"

You can run it with:

fastmcp run server.py:my_server

Factory Function

Since fastmcp run ignores the if __name__ == "__main__" block, you can use a factory function to run setup code before your server starts. Factory functions are called without any arguments and must return a FastMCP server instance. Both sync and async factory functions are supported.

The syntax for using a factory function is the same as for an explicit server entrypoint: fastmcp run server.py:factory_fn. FastMCP will automatically detect that you have identified a function rather than a server Instance

For example, if you have a file called server.py with the following content:

from fastmcp import FastMCP

async def create_server() -> FastMCP:
    mcp = FastMCP("MyServer")
    
    @mcp.tool
    def add(x: int, y: int) -> int:
        return x + y
    
    # Setup that runs with fastmcp run
    tool = await mcp.get_tool("add")
    tool.disable()
    
    return mcp

You can run it with:

fastmcp run server.py:create_server

Remote Server Proxy

FastMCP run can also start a local proxy server that connects to a remote server. This is useful when you want to run a remote server locally for testing or development purposes, or to use with a client that doesn't support direct connections to remote servers.

To start a local proxy, you can use the following syntax:

fastmcp run https://example.com/mcp

FastMCP Configuration

FastMCP supports declarative configuration through fastmcp.json files. When you run fastmcp run without arguments, it automatically looks for a fastmcp.json file in the current directory:

# Auto-detect fastmcp.json in current directory
fastmcp run

# Or explicitly specify a configuration file
fastmcp run my-config.fastmcp.json

The configuration file handles dependencies, environment variables, and transport settings. Command-line arguments override configuration file values:

# Override port from config file
fastmcp run fastmcp.json --port 8080

# Skip environment setup when already in a uv environment
fastmcp run fastmcp.json --skip-env

See Server Configuration for detailed documentation on fastmcp.json.

MCP Configuration

FastMCP can also run servers defined in a standard MCP configuration file. This is useful when you want to run multiple servers from a single file, or when you want to use a client that doesn't support direct connections to remote servers.

To run a MCP configuration file, you can use the following syntax:

fastmcp run mcp.json

This will run all the servers defined in the file.

fastmcp dev

Run a MCP server with the MCP Inspector for testing.

fastmcp dev server.py

When using fastmcp.json, the dev command automatically uses the configured dependencies. </Tip>

This command does not support HTTP testing. To test a server over Streamable HTTP or SSE:

1. Start your server manually with the appropriate transport using either the command line:
   bashCopy

   fastmcp run server.py --transport http
   

   or by setting the transport in your code:
   bashCopy

   python server.py  # Assuming your __main__ block sets Streamable HTTP transport
   

2. Open the MCP Inspector separately and connect to your running server </Warning>

Options

Entrypoints

The dev command supports local FastMCP server files and configuration:

1. Inferred server instance: server.py - imports the module and looks for a FastMCP server instance named mcp, server, or app. Errors if no such object is found.
2. Explicit server entrypoint: server.py:custom_name - imports and uses the specified server entrypoint
3. Factory function: server.py:create_server - calls the specified function (sync or async) to create a server instance
4. FastMCP configuration: fastmcp.json - uses FastMCP's declarative configuration (auto-detects in current directory)

Examples

# Run dev server with editable mode and additional packages
fastmcp dev server.py -e . --with pandas --with matplotlib

# Run dev server with fastmcp.json configuration (auto-detects)
fastmcp dev

# Run dev server with explicit fastmcp.json file
fastmcp dev dev.fastmcp.json

# Run dev server with specific Python version
fastmcp dev server.py --python 3.11

# Run dev server with requirements file
fastmcp dev server.py --with-requirements requirements.txt

# Run dev server within a specific project directory
fastmcp dev server.py --project /path/to/project

fastmcp install

Install a MCP server in MCP client applications. FastMCP currently supports the following clients:

• Claude Code - Installs via Claude Code's built-in MCP management system
• Claude Desktop - Installs via direct configuration file modification
• Cursor - Installs via deeplink that opens Cursor for user confirmation
• MCP JSON - Generates standard MCP JSON configuration for manual use

fastmcp install claude-code server.py
fastmcp install claude-desktop server.py
fastmcp install cursor server.py
fastmcp install mcp-json server.py

Note that for security reasons, MCP clients usually run every server in a completely isolated environment. Therefore, all dependencies must be explicitly specified using the --with and/or --with-editable options (following uv conventions) or by attaching them to your server in code via the dependencies parameter. You should not assume that the MCP server will have access to your local environment.

Options

Entrypoints

The install command supports local FastMCP server files and configuration:

1. Inferred server instance: server.py - imports the module and looks for a FastMCP server instance named mcp, server, or app. Errors if no such object is found.
2. Explicit server entrypoint: server.py:custom_name - imports and uses the specified server entrypoint
3. Factory function: server.py:create_server - calls the specified function (sync or async) to create a server instance
4. FastMCP configuration: fastmcp.json - uses FastMCP's declarative configuration with dependencies and settings

Examples

# Auto-detects server entrypoint (looks for 'mcp', 'server', or 'app')
fastmcp install claude-desktop server.py

# Install with fastmcp.json configuration (auto-detects)
fastmcp install claude-desktop

# Install with explicit fastmcp.json file
fastmcp install claude-desktop my-config.fastmcp.json

# Uses specific server entrypoint
fastmcp install claude-desktop server.py:my_server

# With custom name and dependencies
fastmcp install claude-desktop server.py:my_server --server-name "My Analysis Server" --with pandas

# Install in Claude Code with environment variables
fastmcp install claude-code server.py --env API_KEY=secret --env DEBUG=true

# Install in Cursor with environment variables
fastmcp install cursor server.py --env API_KEY=secret --env DEBUG=true

# Install with environment file
fastmcp install cursor server.py --env-file .env

# Install with specific Python version
fastmcp install claude-desktop server.py --python 3.11

# Install with requirements file
fastmcp install claude-code server.py --with-requirements requirements.txt

# Install within a project directory
fastmcp install cursor server.py --project /path/to/project

# Generate MCP JSON configuration
fastmcp install mcp-json server.py --name "My Server" --with pandas

# Copy JSON configuration to clipboard
fastmcp install mcp-json server.py --copy

MCP JSON Generation

The mcp-json subcommand generates standard MCP JSON configuration that can be used with any MCP-compatible client. This is useful when:

• Working with MCP clients not directly supported by FastMCP
• Creating configuration for CI/CD environments
• Sharing server configurations with others
• Integration with custom tooling

The generated JSON follows the standard MCP server configuration format used by Claude Desktop, VS Code, Cursor, and other MCP clients, with the server name as the root key:

{
  "server-name": {
    "command": "uv",
    "args": [
      "run",
      "--with",
      "fastmcp",
      "fastmcp",
      "run",
      "/path/to/server.py"
    ],
    "env": {
      "API_KEY": "value"
    }
  }
}

Options specific to mcp-json:

fastmcp inspect

Inspect a FastMCP server to view summary information or generate a detailed JSON report.

# Show text summary
fastmcp inspect server.py

# Output FastMCP JSON to stdout
fastmcp inspect server.py --format fastmcp

# Save MCP JSON to file (format required with -o)
fastmcp inspect server.py --format mcp -o manifest.json

Options

Output Formats

FastMCP Format (--format fastmcp)

The default and most comprehensive format, includes all FastMCP-specific metadata:

• Server name, instructions, and version
• FastMCP version and MCP version
• Tool tags and enabled status
• Output schemas for tools
• Annotations and custom metadata
• Uses snake_case field names
• Use this for: Complete server introspection and debugging FastMCP servers

MCP Protocol Format (--format mcp)

Shows exactly what MCP clients will see via the protocol:

• Only includes standard MCP protocol fields
• Matches output from client.list_tools(), client.list_prompts(), etc.
• Uses camelCase field names (e.g., inputSchema)
• Excludes FastMCP-specific fields like tags and enabled status
• Use this for: Debugging client visibility and ensuring MCP compatibility

Entrypoints

The inspect command supports local FastMCP server files and configuration:

1. Inferred server instance: server.py - imports the module and looks for a FastMCP server instance named mcp, server, or app. Errors if no such object is found.
2. Explicit server entrypoint: server.py:custom_name - imports and uses the specified server entrypoint
3. Factory function: server.py:create_server - calls the specified function (sync or async) to create a server instance
4. FastMCP configuration: fastmcp.json - inspects servers defined with FastMCP's declarative configuration

Examples

# Show text summary (no JSON output)
fastmcp inspect server.py
# Output: 
# Server: MyServer
# Instructions: A helpful MCP server
# Version: 1.0.0
#
# Components:
#   Tools: 5
#   Prompts: 2
#   Resources: 3
#   Templates: 1
#
# Environment:
#   FastMCP: 2.0.0
#   MCP: 1.0.0
#
# Use --format [fastmcp|mcp] for complete JSON output

# Output FastMCP format to stdout
fastmcp inspect server.py --format fastmcp

# Specify server entrypoint
fastmcp inspect server.py:my_server

# Output MCP protocol format to stdout
fastmcp inspect server.py --format mcp

# Save to file (format required)
fastmcp inspect server.py --format fastmcp -o server-manifest.json

# Save MCP format with custom server object
fastmcp inspect server.py:my_server --format mcp -o mcp-manifest.json

# Error: format required with output file
fastmcp inspect server.py -o output.json
# Error: --format is required when using -o/--output

fastmcp project prepare

Create a persistent uv project directory from a fastmcp.json file's environment configuration. This allows you to pre-install all dependencies once and reuse them with the --project flag.

fastmcp project prepare fastmcp.json --output-dir ./env

Options

Usage Pattern

# Step 1: Prepare the environment (installs dependencies)
fastmcp project prepare fastmcp.json --output-dir ./my-env

# Step 2: Run using the prepared environment (fast, no dependency installation)
fastmcp run fastmcp.json --project ./my-env

The prepare command creates a uv project with:

• A pyproject.toml containing all dependencies from the fastmcp.json
• A .venv with all packages pre-installed
• A uv.lock file for reproducible environments

This is useful when you want to separate environment setup from server execution, such as in deployment scenarios where dependencies are installed once and the server is run multiple times.

fastmcp version

Display version information about FastMCP and related components.

fastmcp version

Options