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The MCP Inspector can be run directly from the command line using npx, making it easy to quickly inspect and debug MCP servers without installing anything globally.

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Quick Start

Run the inspector with a single command: 
npx @mcp-use/inspector
This will:
  • Start the inspector server on an available port (default: 8080)
  • Automatically open your browser to the inspector interface
  • Display the URL in the terminal

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Command Options

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--url <url>

Auto-connect to an MCP server when the inspector starts. 
npx @mcp-use/inspector --url http://localhost:3000/mcp
Example URLs:
  • Local server: http://localhost:3000/mcp
  • Remote server: https://mcp.linear.app/mcp
  • WebSocket: ws://localhost:8080/mcp
The URL must start with http://, https://, ws://, or wss://. The inspector will validate the URL format before starting.

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--port <port>

Specify the starting port number. The inspector will find the next available port if the specified port is already in use. 
npx @mcp-use/inspector --port 9000
Default: 8080 Port Range: Must be between 1 and 65535

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--help, -h

Display help information and available options. 
npx @mcp-use/inspector --help

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Automatic Port Selection

If the specified port (or default 8080) is already in use, the inspector will automatically try the next available port. The terminal output will show the actual port being used: 
🚀 MCP Inspector running on http://localhost:8081
📡 Auto-connecting to: http://localhost:3000/mcp
🌐 Browser opened

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Troubleshooting

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Port Already in Use

If you see an error about the port being in use: 
# Try a different port
npx @mcp-use/inspector --port 9000

# Or stop the process using the port
lsof -ti:8080 | xargs kill

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Invalid URL Format

Ensure your URL starts with a valid protocol: 
# ✅ Valid
npx @mcp-use/inspector --url http://localhost:3000/mcp
npx @mcp-use/inspector --url https://mcp.example.com/mcp

# ❌ Invalid
npx @mcp-use/inspector --url localhost:3000/mcp

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Browser Doesn’t Open

If the browser doesn’t open automatically, check the terminal output for the inspector URL and open it manually.