Client-Only Package - Fastmcp

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

FastMCP's full fastmcp package includes everything needed to build and run MCP servers, apps, proxies, and clients. If you are only embedding an MCP client in another framework, building your own LLM host, or testing MCP servers, you can install the smaller client-only package instead.

bash

pip install "fastmcp-slim[client]"

The client-only package uses the fastmcp import namespace:

python

from fastmcp import Client

client = Client("https://example.com/mcp")

Use fastmcp-slim[client] when your code connects to MCP servers but does not define or run FastMCP servers itself. For example, framework authors can depend on fastmcp-slim[client] to provide MCP connectivity without requiring users to install the full FastMCP server stack.

Supported Usage

Client-only installs support remote and subprocess transports:

python

from fastmcp import Client

# Remote MCP server
http_client = Client("https://example.com/mcp")

# Local MCP server over stdio
stdio_client = Client("my_server.py")

Single-server MCP configuration works as well:

python

from fastmcp import Client

config = {
    "mcpServers": {
        "weather": {
            "url": "https://weather.example.com/mcp"
        }
    }
}

client = Client(config)

Optional sampling handlers are available through the same extras as the full package:

bash

pip install "fastmcp-slim[client,openai]"
pip install "fastmcp-slim[client,anthropic]"
pip install "fastmcp-slim[client,gemini]"

When to Use the Full Package

Install fastmcp when you need server-side FastMCP features:

bash

pip install fastmcp

The full package remains the default for most users and continues to support the existing import style:

python

from fastmcp import Client, FastMCP

server = FastMCP("Example")
client = Client(server)

Use the full package for:

defining or running FastMCP servers
in-memory clients connected directly to FastMCP server objects
multi-server MCP configurations
FastMCP apps, proxies, server auth, middleware, and other server-side features

The fastmcp-slim package is intentionally narrower: it is for client-only consumers who want FastMCP's MCP client behavior without depending on the full framework.