ERR_NGROK_334: The endpoint URL is already online

What does ERR_NGROK_334 mean?

ngrok returns ERR_NGROK_334 with this message:

The endpoint <URL> is already online. Either
1. stop your existing endpoint first, or
2. start both endpoints with `--pooling-enabled` to load balance between them.

Troubleshoot ERR_NGROK_334 with your AI agent. Connect it to the ngrok MCP server, then ask what caused the error and how to fix it.

Why does ngrok return ERR_NGROK_334?

You can only use a tunnel URL for one tunnel session at a time. This error occurs when an ngrok tunnel with the requested URL is already online. This error also appears if you attempt to create multiple tunnels using the same hostname.

You can view tunnel status from your dashboard.
You can also view actively connected agents from your dashboard. Select one from the list to view any tunnels that agent is handling.

How do I fix ERR_NGROK_334?

Stop the tunnel that is currently running to make your desired URL available.
Choose a different unique URL or hostname to start your tunnel.

Where can I get more help with ERR_NGROK_334?

Email support@ngrok.com and include the error code.