The Tunels request inspector at localhost:4040 is one of the most powerful debugging tools available to developers. Every HTTP request that flows through your tunnel is captured and displayed in real-time.

Accessing the Inspector

When you start a tunnel, the inspector automatically starts on port 4040:

tunels http 3000
# Inspector: http://localhost:4040

Open it in your browser to see a real-time feed of all requests.

What You Can See

For each request, the inspector shows:

  • Method and URL — GET, POST, PUT, DELETE, PATCH
  • Request headers — Content-Type, Authorization, custom headers
  • Request body — JSON, form data, raw bytes
  • Response status — 200, 404, 500, etc.
  • Response headers and body
  • Timing — how long the request took

Debugging Webhook Integrations

The inspector is invaluable when integrating webhooks. You can see the exact payload a service sends, including headers you might not think to log. For example, Stripe's webhook includes:

  • Stripe-Signature header for verification
  • Content-Type: application/json
  • The full event object in the body

If your handler returns a 500 error, you can see both the incoming request and your server's error response side by side.

Replaying Requests

Failed a webhook? Instead of triggering a new event from the provider's dashboard, use the replay feature in the inspector. Click "Replay" on any captured request to re-send it to your local server. This is much faster than generating new test events.

Filtering and Searching

When dealing with high-traffic tunnels, use the inspector's search to filter by URL path, status code, or method. This helps you find the specific request you're debugging among hundreds of others.

Conclusion

The request inspector turns Tunels from a simple proxy into a powerful debugging tool. Use it to understand exactly what's happening between your services and the outside world.