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What does ERR_NGROK_108 mean?

ngrok returns ERR_NGROK_108 with this message:
Troubleshoot ERR_NGROK_108 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_108?

An ngrok account is limited in how many agents it can simultaneously run. This limit is listed for each plan as “online ngrok processes” on the pricing page. This error indicates you’ve exceeded that limit. The list of online ngrok processes is visible in the dashboard.

How do I fix ERR_NGROK_108?

Running multiple tunnels with one agent

Make sure you’re not accidentally leaving any unnecessary ngrok agent sessions open. Stopping any agent processes that aren’t necessary frees up that resource so you can use it elsewhere in your setup. You may think you need to use multiple agents to accomplish the goal of tunneling to multiple services, but if all of your services are reachable from a single machine then you can configure a single ngrok agent running on that machine to tunnel to multiple services within a single agent session. The ngrok agent supports running multiple tunnels using either the configuration file or the ngrok agent api. It is possible for one agent to start multiple tunnels simultaneously. This number varies depending on which plan you’ve selected. See the pricing page’s “tunnels / ngrok process” feature for how many tunnels you may run with one agent.

Upgrade your plan

You might consider upgrading your plan to one that offers more simultaneous agent sessions.

Purchase additional licenses

You can purchase additional licenses by adding members to your team if you need the agent to run on multiple devices or run more tunnels.

Where can I get more help with ERR_NGROK_108?

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