Practical MCP with FastMCP & LangChain

FastMCP with MCP Inspector

To make development easier, you can use the MCP Inspector, the web-based tool that we already used in the previous chapters. It's a great way to visualize and test your MCP server in real-time.

FastMCP provides a convenient fastmcp dev inspector command that automatically launches your server with the MCP Inspector. However, this command only works with STDIO transport - it doesn't support HTTP.

Since our current fastmcp.json is configured for HTTP transport, we have two options:

Option 1: Use STDIO with the Inspector:

Create a separate configuration file for development with STDIO:

cd $HOME/workspace/fastmcp_demo && cat > dev.fastmcp.json <
{
  "\$schema": "https://gofastmcp.com/public/schemas/fastmcp.json/v1.json",
  "source": {
    "path": "server.py",
    "entrypoint": "mcp"
  },
  "deployment": {
    "transport": "stdio",
    "log_level": "INFO"
  }
}
EOF

Then launch the Inspector with:

# cd $HOME/workspace/fastmcp_demo

# This will start the server with STDIO transport and open the Inspector
uv run fastmcp dev inspector dev.fastmcp.json