# Debugging and Development Workflow for MCP Integrations
Effective debugging is crucial for developing Model Context Protocol (MCP) servers and integrating them with applications. This guide provides a comprehensive overview of the debugging tools and approaches available within the MCP ecosystem.
## Debugging Tools Overview
MCP offers several tools designed for debugging at different levels of the integration:
1. **MCP Inspector**: An interactive debugging interface primarily used for direct server testing and development.
2. **Claude Desktop Developer Tools**: Used for integration testing, log collection, and leveraging Chrome DevTools within the Claude Desktop application.
3. **Server Logging**: Involves custom logging implementations within your MCP server for error tracking and performance monitoring.
## Debugging in Claude Desktop
Claude Desktop provides built-in functionalities and integrations to assist with debugging MCP servers.
### Checking Server Status
The Claude.app interface offers basic status information for connected MCP servers:
* Click the <img src="/images/claude-desktop-mcp-plug-icon.svg" style={{display: 'inline', margin: 0, height: '1.3em'}} /> icon to view:
* Currently connected servers.
* Available prompts and resources provided by these servers.
* Click the <img src="/images/claude-desktop-mcp-hammer-icon.svg" style={{display: 'inline', margin: 0, height: '1.3em'}} /> icon to view:
* Tools that have been made available to the model by the connected servers.
### Viewing Logs
Detailed MCP logs from Claude Desktop can be reviewed to understand server connection events, configuration issues, runtime errors, and message exchanges.
To follow logs in real-time on macOS, use the following command in your terminal:
```bash
tail -n 20 -F ~/Library/Logs/Claude/mcp*.log
```
### Using Chrome DevTools
Chrome's developer tools can be accessed within Claude Desktop to investigate client-side errors and network activity.
1. **Enable DevTools**: Create a `developer_settings.json` file in your Claude application support directory with `allowDevTools` set to `true`:
```bash
echo '{"allowDevTools": true}' > ~/Library/Application\ Support/Claude/developer_settings.json
```
2. **Open DevTools**: Press `Command-Option-Shift-i` (on macOS).
* Note that two DevTools windows may appear: one for the main content and one for the app title bar.
Within DevTools, you can use:
* The **Console panel** to inspect client-side errors.
* The **Network panel** to inspect message payloads and connection timing.
## Common Issues
Several common issues can arise during MCP integration and development.
### Working Directory
When MCP servers are launched via `claude_desktop_config.json` in Claude Desktop, their working directory may be undefined (e.g., `/` on macOS) because Claude Desktop can be started from any location.
* **Resolution**: Always use absolute paths in your server configurations and `.env` files to ensure reliable operation.
* **Example**: In `claude_desktop_config.json`, use an absolute path for commands:
```json
{
"command": "npx",
"args": ["-y", "@modelcontextprotocol/server-filesystem", "/Users/username/data"]
}
```
Avoid relative paths like `./data`.
For testing servers directly via the command line, the working directory will be the directory from which you execute the command.
### Environment Variables
MCP servers automatically inherit only a subset of environment variables (e.g., `USER`, `HOME`, `PATH`).
* **Resolution**: To override default variables or provide custom ones, specify an `env` key within your `claude_desktop_config.json`:
```json
{
"myserver": {
"command": "mcp-server-myapp",
"env": {
"MYAPP_API_KEY": "some_key"
}
}
}
```
### Server Initialization
Common problems during server initialization include:
* **Path Issues**: Incorrect server executable paths, missing required files, or permission problems. Try using an absolute path for the `command` in your configuration.
* **Configuration Errors**: Invalid JSON syntax, missing required fields, or type mismatches in your configuration files.
* **Environment Problems**: Missing environment variables, incorrect variable values, or permission restrictions.
### Connection Problems
If servers fail to connect to Claude Desktop:
1. Check the Claude Desktop logs for error messages.
2. Verify that the server process is running.
3. Test the server standalone using the MCP Inspector to isolate the issue.
4. Verify protocol compatibility between the client and server.
## Implementing Logging
Effective logging is vital for understanding server behavior and troubleshooting.
### Server-Side Logging
For servers using the local stdio transport, messages logged to `stderr` (standard error) are automatically captured by the host application (e.g., Claude Desktop).
**Important**: Local MCP servers should **not** log messages to `stdout` (standard out), as this will interfere with the protocol's operation.
For all transports, you can also send log messages directly to the client using a log message notification:
<Tabs>
<Tab title="Python">
```python
server.request_context.session.send_log_message(
level="info",
data="Server started successfully",
)
```
</Tab>
<Tab title="TypeScript">
```typescript
server.sendLoggingMessage({
level: "info",
data: "Server started successfully",
});
```
</Tab>
</Tabs>
Important events to log include:
* Initialization steps
* Resource access
* Tool execution
* Error conditions
* Performance metrics
### Client-Side Logging
In client applications, consider:
1. Enabling debug logging.
2. Monitoring network traffic.
3. Tracking message exchanges.
4. Recording error states.
## Debugging Workflow
A structured workflow can streamline the debugging process.
### Development Cycle
1. **Initial Development**:
* Use the MCP Inspector for basic testing of core functionality.
* Implement core features and add logging points.
2. **Integration Testing**:
* Test the server within Claude Desktop.
* Monitor logs for issues.
* Check error handling.
### Testing Changes
To test changes efficiently:
* **Configuration changes**: Restart Claude Desktop to apply new configurations.
* **Server code changes**: Use `Command-R` (on macOS) to reload the server within Claude Desktop.
* **Quick iteration**: Use the MCP Inspector during development for rapid testing and iteration.
## Best Practices
### Logging Strategy
1. **Structured Logging**: Use consistent formats, include context (e.g., request IDs), add timestamps, and track request IDs.
2. **Error Handling**: Log stack traces, include error context, track error patterns, and monitor recovery mechanisms.
3. **Performance Tracking**: Log operation timing, monitor resource usage, track message sizes, and measure latency.
### Security Considerations
When debugging, be mindful of security:
1. **Sensitive Data**: Sanitize logs to protect credentials and mask personal information.
2. **Access Control**: Verify permissions and authentication, and monitor access patterns.
## Getting Help
When encountering issues, follow these steps:
1. **First Steps**: Check server logs, test with the MCP Inspector, review configuration files, and verify the environment.
2. **Support Channels**: Utilize GitHub issues or GitHub discussions for community support.
3. **Providing Information**: When seeking help, provide log excerpts, configuration files, clear steps to reproduce the issue, and environment details.
## MCP Inspector
The MCP Inspector is an interactive developer tool specifically designed for testing and debugging MCP servers. It provides a detailed view into the server's capabilities and message exchanges.
### Installation and Basic Usage
The Inspector can be run directly using `npx` without requiring a global installation:
```bash
npx @modelcontextprotocol/inspector <command>
```
Or with arguments:
```bash
npx @modelcontextprotocol/inspector <command> <arg1> <arg2>
```
#### Inspecting Servers from NPM or PyPi
To inspect server packages distributed via NPM or PyPi:
<Tabs>
<Tab title="NPM package">
```bash
npx -y @modelcontextprotocol/inspector npx <package-name> <args>
# For example
npx -y @modelcontextprotocol/inspector npx server-postgres postgres://127.0.0.1/testdb
```
</Tab>
<Tab title="PyPi package">
```bash
npx @modelcontextprotocol/inspector uvx <package-name> <args>
# For example
npx @modelcontextprotocol/inspector uvx mcp-server-git --repository ~/code/mcp/servers.git
```
</Tab>
</Tabs>
#### Inspecting Locally Developed Servers
For servers developed locally or downloaded as a repository:
<Tabs>
<Tab title="TypeScript">
```bash
npx @modelcontextprotocol/inspector node path/to/server/index.js args...
```
</Tab>
<Tab title="Python">
```bash
npx @modelcontextprotocol/inspector \
uv \
--directory path/to/server \
run \
package-name \
args...
```
</Tab>
</Tabs>
Always refer to the specific server's README for the most accurate instructions.
### Feature Overview
The MCP Inspector interface provides several key features for interacting with your MCP server:
* **Server Connection Pane**: Allows selecting the transport for connecting to the server and customizing command-line arguments and environment variables for local servers.
* **Resources Tab**: Lists all available resources, displays their metadata (MIME types, descriptions), allows content inspection, and supports subscription testing.
* **Prompts Tab**: Displays available prompt templates, shows their arguments and descriptions, enables testing prompts with custom arguments, and previews generated messages.
* **Tools Tab**: Lists available tools, shows their schemas and descriptions, enables testing tools with custom inputs, and displays tool execution results.
* **Notifications Pane**: Presents all logs recorded from the server and shows notifications received from the server.
### Best Practices for Inspector Usage
### Development Workflow
1. **Start Development**: Launch the Inspector with your server, verify basic connectivity, and check capability negotiation.
2. **Iterative Testing**: Make server changes, rebuild the server, reconnect the Inspector, and test affected features while monitoring messages.
3. **Test Edge Cases**: Test with invalid inputs, missing prompt arguments, and concurrent operations. Verify proper error handling and error responses.
