> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/punkpeye/fastmcp/llms.txt
> Use this file to discover all available pages before exploring further.

# fastmcp inspect

> Debug MCP servers with the visual MCP Inspector interface

The `fastmcp inspect` command launches the MCP Inspector, a visual debugging tool that provides a web-based interface for testing and debugging your MCP server.

## Command Syntax

```bash theme={null}
npx fastmcp inspect <file>
```

### Arguments

* `<file>` - **Required**. Path to your server file (TypeScript or JavaScript)

## Basic Usage

Launch the inspector for your server:

```bash theme={null}
npx fastmcp inspect src/server.ts
```

This command:

1. Starts your MCP server
2. Launches the MCP Inspector web interface
3. Automatically opens your browser to the inspector UI
4. Connects the inspector to your running server

## What is MCP Inspector?

MCP Inspector ([@modelcontextprotocol/inspector](https://github.com/modelcontextprotocol/inspector)) is an official visual debugging tool from the Model Context Protocol team. It provides:

* **Interactive Tool Testing** - Execute tools with a visual form interface
* **Resource Browser** - Browse and preview resources with syntax highlighting
* **Prompt Testing** - Test prompts and view generated content
* **Real-time Logs** - Monitor server logs and events
* **Request/Response Viewer** - Inspect MCP protocol messages
* **Schema Validation** - Verify tool parameters and responses

## Examples

<CodeGroup>
  ```bash Inspect Server theme={null}
  npx fastmcp inspect src/examples/addition.ts
  ```

  ```bash Inspect Custom Server theme={null}
  npx fastmcp inspect src/my-server.ts
  ```

  ```bash From Project Root theme={null}
  cd fastmcp
  npx fastmcp inspect src/examples/addition.ts
  ```
</CodeGroup>

## Inspector Interface

### Tools Tab

The Tools tab allows you to:

* View all available tools and their descriptions
* See tool parameter schemas
* Fill in parameters using a visual form
* Execute tools and view results
* Test error handling

### Resources Tab

The Resources tab provides:

* List of all available resources and templates
* Resource URI structure
* Preview resource contents
* Test resource templates with different arguments
* View MIME types and metadata

### Prompts Tab

The Prompts tab enables:

* Browse available prompts
* Test prompt argument completion
* Preview generated prompt messages
* Inspect prompt metadata

### Logs Tab

The Logs tab displays:

* Server startup logs
* Tool execution logs
* Error messages and stack traces
* Protocol-level messages
* Connection events

## Transport Compatibility

The inspect command works with servers using the `stdio` transport:

```typescript src/server.ts theme={null}
import { FastMCP } from "fastmcp";

const server = new FastMCP({
  name: "My Server",
  version: "1.0.0",
});

// Add your tools, resources, and prompts...

server.start({
  transportType: "stdio", // Compatible with inspector
});
```

<Note>
  For HTTP-based servers (`httpStream`, `sse`), you should run your server separately and configure the inspector to connect via HTTP instead of using the CLI command.
</Note>

## Debugging Workflow

Here's a recommended workflow for debugging with the inspector:

1. **Start the Inspector**
   ```bash theme={null}
   npx fastmcp inspect src/server.ts
   ```

2. **Verify Server Connection**
   * Check that the server appears connected in the UI
   * Review the server name and version

3. **Test Tools**
   * Navigate to the Tools tab
   * Select a tool to test
   * Fill in required parameters
   * Execute and verify the response

4. **Browse Resources**
   * Switch to the Resources tab
   * Test resource URIs
   * Verify resource content and MIME types

5. **Monitor Logs**
   * Keep the Logs tab open
   * Watch for errors or warnings
   * Verify log messages from your tools

## Troubleshooting

### Inspector Won't Start

If the inspector fails to launch:

```bash theme={null}
# Check if the server file is valid
npx fastmcp validate src/server.ts

# Try running with dev command first
npx fastmcp dev src/server.ts --verbose
```

### Browser Doesn't Open

If the browser doesn't open automatically:

* Check the terminal for the inspector URL
* Manually open the URL in your browser
* Ensure no firewall is blocking the connection

### Connection Issues

If the inspector shows "Disconnected":

* Verify your server is using `stdio` transport
* Check for errors in the Logs tab
* Restart the inspector command

## Comparison with Dev Command

| Feature          | `fastmcp dev`   | `fastmcp inspect`   |
| ---------------- | --------------- | ------------------- |
| Interface        | Terminal CLI    | Web Browser         |
| Tool Testing     | Text-based      | Visual Forms        |
| Resource Preview | Text output     | Syntax Highlighting |
| Logs             | Terminal output | Dedicated tab       |
| Best For         | Quick testing   | In-depth debugging  |

## Related Commands

<CardGroup cols={2}>
  <Card title="Dev Command" icon="terminal" href="/cli/dev">
    Run servers with interactive CLI
  </Card>

  <Card title="CLI Overview" icon="list" href="/cli/overview">
    Back to CLI overview
  </Card>
</CardGroup>

## Learn More

<Card title="MCP Inspector GitHub" icon="github" href="https://github.com/modelcontextprotocol/inspector">
  Official MCP Inspector repository and documentation
</Card>