As you develop Model Context Protocol (MCP) servers, having the right tools to test and debug your implementations becomes crucial. The MCP Inspector provides a user-friendly interface to interact with, test, and validate your MCP servers during development.
What is the MCP Inspector?
The MCP Inspector is a specialized development tool designed specifically for working with MCP servers. It provides:
- A visual interface to inspect MCP server connections
- Real-time monitoring of request/response cycles
- Capability testing and validation
- Authentication support for secure connections
Why Use the MCP Inspector?
Developing MCP servers without proper testing tools can be challenging. The MCP Inspector solves common development problems:
- Visibility: See exactly what's happening in your MCP server's request/response cycle
- Debugging: Identify issues in your implementation faster with detailed logs
- Validation: Ensure your server follows the MCP specification correctly
- Efficiency: Test changes without setting up full client applications
Running the Inspector
There are multiple ways to use the MCP Inspector depending on your specific needs.
From an MCP Server Repository
The simplest way to use the inspector is directly with npx, without needing to clone the inspector repository:
For standard usage, just point the inspector at your server implementation:
This will start both the inspector UI and proxy server with default settings.
Once started, the inspector runs:
- An MCP Inspector (MCPI) client UI (default port 6274)
- An MCP Proxy (MCPP) server (default port 6277)
Open the MCPI client UI in your browser to start inspecting your server.
From the Inspector Repository
If you're working on the inspector itself or prefer a local installation:
For standard development mode:
This will start the inspector in development mode with hot reloading.
Authentication Support
The MCP Inspector supports secure connections with bearer token authentication for SSE connections:
- Enter your authentication token in the UI when connecting to an MCP server
- The token will be sent in the Authorization header for all requests
- This allows testing of secured MCP implementations
Be careful with sensitive authentication tokens. The MCP Inspector is a development tool and should not be used in production environments with real credentials.
Security Considerations
When using the MCP Inspector, keep these security aspects in mind:
- The proxy server has permissions to spawn local processes
- It can connect to any specified MCP server
- The proxy should not be exposed to untrusted networks
- Use it only in development environments
Configuration Options
The inspector supports several configuration settings that can be adjusted through the UI:
| Setting | Description | Default |
|---|---|---|
| MCP_SERVER_REQUEST_TIMEOUT | Timeout for requests to the MCP server (ms) | 10000 |
| MCP_REQUEST_TIMEOUT_RESET_ON_PROGRESS | Reset timeout on progress notifications | true |
| MCP_REQUEST_MAX_TOTAL_TIMEOUT | Maximum total timeout for requests with progress notifications (ms) | 60000 |
| MCP_PROXY_FULL_ADDRESS | Custom address for MCP Inspector Proxy (e.g., http://10.1.1.22:5577) | "" |
These settings can be adjusted in real-time through the UI and will persist across sessions.
Best Practices for Testing with the Inspector
Here are some tips for effectively using the MCP Inspector in your development workflow:
- Start Small: Begin by testing basic capabilities before moving to more complex features
- Methodical Testing: Test one capability at a time to isolate issues
- Edge Cases: Use the inspector to manually test edge cases and error handling
- Authentication Flow: Verify your authentication handling works correctly
- Performance Testing: Monitor response times for different request types
Troubleshooting
If you encounter issues with the MCP Inspector:
- Ensure your MCP server is running and accessible
- Check the specified ports are not already in use
- Verify environment variables are correctly formatted
- Review console logs for error messages
- For Windows users, ensure you're using the Windows-specific commands
Next Steps
After becoming familiar with the MCP Inspector:
- Integrate it into your development workflow
- Create automated test scripts that utilize the inspector
- Contribute to the inspector's development with feedback and feature requests
- Explore the debugging guide for advanced techniques
For the latest updates on the MCP Inspector, check the official repository at github.com/modelcontextprotocol/inspector.
The MCP Inspector is an invaluable tool in your MCP development toolkit, helping you build robust, compliant, and reliable MCP servers. As the MCP ecosystem grows, tools like the inspector will continue to evolve to meet developers' needs.