Debugging
A comprehensive guide to debugging Model Context Protocol (MCP) integrations
Effective debugging is essential when developing MCP servers or integrating them with applications. This guide covers the debugging tools and approaches available in the MCP ecosystem.
This guide is for macOS. Guides for other platforms are coming soon.
Debugging tools overview
MCP provides several tools for debugging at different levels:
-
MCP Inspector
- Interactive debugging interface
- Direct server testing
- See the Inspector guide for details
-
Claude Desktop Developer Tools
- Integration testing
- Log collection
- Chrome DevTools integration
-
Server Logging
- Custom logging implementations
- Error tracking
- Performance monitoring
Debugging in Claude Desktop
Checking server status
The Claude.app interface provides basic server status information:
-
Click the π icon to view:
- Connected servers
- Available prompts and resources
-
Click the π¨ icon to view:
- Tools made available to the model
Viewing logs
Review detailed MCP logs from Claude Desktop:
The logs capture:
- Server connection events
- Configuration issues
- Runtime errors
- Message exchanges
Using Chrome DevTools
Access Chromeβs developer tools inside Claude Desktop to investigate client-side errors:
- Enable DevTools:
- Open DevTools:
Command-Option-Shift-i
Note: Youβll see two DevTools windows:
- Main content window
- App title bar window
Use the Console panel to inspect client-side errors.
Use the Network panel to inspect:
- Message payloads
- Connection timing
Common issues
Environment variables
MCP servers inherit only a subset of environment variables automatically, like USER
, HOME
, and PATH
.
To override the default variables or provide your own, you can specify an env
key in claude_desktop_config.json
:
Server initialization
Common initialization problems:
-
Path Issues
- Incorrect server executable path
- Missing required files
- Permission problems
-
Configuration Errors
- Invalid JSON syntax
- Missing required fields
- Type mismatches
-
Environment Problems
- Missing environment variables
- Incorrect variable values
- Permission restrictions
Connection problems
When servers fail to connect:
- Check Claude Desktop logs
- Verify server process is running
- Test standalone with Inspector
- Verify protocol compatibility
Implementing logging
Server-side logging
When building a server that uses the local stdio transport, all messages logged to stderr (standard error) will be captured by the host application (e.g., Claude Desktop) automatically.
Local MCP servers should not log messages to stdout (standard out), as this will interfere with protocol operation.
For all transports, you can also provide logging to the client by sending a log message notification:
Important events to log:
- Initialization steps
- Resource access
- Tool execution
- Error conditions
- Performance metrics
Client-side logging
In client applications:
- Enable debug logging
- Monitor network traffic
- Track message exchanges
- Record error states
Debugging workflow
Development cycle
-
Initial Development
- Use Inspector for basic testing
- Implement core functionality
- Add logging points
-
Integration Testing
- Test in Claude Desktop
- Monitor logs
- Check error handling
Testing changes
To test changes efficiently:
- Configuration changes: Restart Claude Desktop
- Server code changes: Use Command-R to reload
- Quick iteration: Use Inspector during development
Best practices
Logging strategy
-
Structured Logging
- Use consistent formats
- Include context
- Add timestamps
- Track request IDs
-
Error Handling
- Log stack traces
- Include error context
- Track error patterns
- Monitor recovery
-
Performance Tracking
- Log operation timing
- Monitor resource usage
- Track message sizes
- Measure latency
Security considerations
When debugging:
-
Sensitive Data
- Sanitize logs
- Protect credentials
- Mask personal information
-
Access Control
- Verify permissions
- Check authentication
- Monitor access patterns
Getting help
When encountering issues:
-
First Steps
- Check server logs
- Test with Inspector
- Review configuration
- Verify environment
-
Support Channels
- GitHub issues
- GitHub discussions
-
Providing Information
- Log excerpts
- Configuration files
- Steps to reproduce
- Environment details
Next steps
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