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The MCP Inspector

🔍 Testing & Debugging⏱ 10 min⭐ 100 BASE XP

Your Best Friend for Debugging

The MCP Inspector is an official interactive debugging tool that connects to any MCP server and lets you explore its capabilities, call tools, read resources, and test prompts — all through a web UI.

Running the Inspector

# For a local stdio server:
npx @modelcontextprotocol/inspector node dist/index.js

# With environment variables:
npx @modelcontextprotocol/inspector \
  -e NOTES_DIR=./notes \
  -e API_KEY=sk-... \
  node dist/index.js

# For a remote SSE server:
npx @modelcontextprotocol/inspector \
  --transport sse \
  --url https://mcp.example.com/sse

What the Inspector Shows

TabWhat It DisplaysWhat You Can Do
ToolsAll registered tools with schemasCall any tool with custom arguments, see responses
ResourcesAll resources and templatesRead resources, browse templates
PromptsAll registered promptsExecute prompts with arguments, see generated messages
NotificationsServer-pushed eventsMonitor real-time notifications
LogsRaw JSON-RPC trafficInspect every protocol message

Inspector Workflow

  1. Launch — Start the inspector with your server command
  2. Verify capabilities — Check all tools, resources, and prompts loaded correctly
  3. Test happy path — Call each tool with valid arguments
  4. Test error path — Call tools with invalid/missing arguments
  5. Check protocol messages — Use the Logs tab to verify JSON-RPC format
🎯 Pro Tip: Add an inspect script to your package.json: "inspect": "npx @modelcontextprotocol/inspector tsx src/index.ts". This makes debugging a one-command operation during development.
SYNAPSE VERIFICATION
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What is the MCP Inspector?
A code linter
An interactive debugging tool with a web UI that connects to MCP servers for testing tools, resources, and prompts
A performance profiler
A security scanner
Watch: 139x Rust Speedup
The MCP Inspector | Testing & Debugging — MCP Academy