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Philosophy

When you encounter an error while using ngrok, we report a globally unique error code. Each error code corresponds to a specific location in ngrok’s code which helps us quickly identify where something went wrong and help you know exactly how to fix it. When your report a bug or email us about a support issue, please include the unique error code if you have encountered one. It will help us diagnose and solve your issue much more quickly. ngrok’s error codes were also designed so that you can paste them into your favorite search engine and immediately find a dedicated page with instructions on how to fix your problem.

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Programmatic Error Handling

When working with ngrok’s programmatically, we return these unique error codes in a structured way so that you can write software which appropriately handles different error conditions.

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Common Errors

You’re more likely to run into some errors than others. The most common are listed here to help make your troubleshooting easier.
CodeMessage
ERR_NGROK_100Invalid metadata length
ERR_NGROK_108You’ve hit your account limit for simultaneous ngrok agent sessions. Try stopping an existing agent or upgrading your account.
ERR_NGROK_120Your ngrok agent version VERSION is no longer supported. Only the most recent version of the ngrok agent is supported without an account. Update to a newer version with ngrok update or by downloading from https://download.ngrok.com. Sign up for an account to avoid forced version upgrades: https://ngrok.com/signup.
ERR_NGROK_1205You failed to solve the catpcha, please try again.
ERR_NGROK_1226You are disallowed from creating an ngrok account due to violation of the terms of service.
ERR_NGROK_3004ngrok gateway error. The server returned an invalid or incomplete HTTP response. Try starting ngrok with the full upstream service URL (for example, ngrok http https://localhost:8081)
ERR_NGROK_3200Tunnel not found. This could be because your agent is not online or your tunnel has been flagged by our automated moderation system.
ERR_NGROK_3208The account associated with this hostname has been banned.We’ve determined this account to be in violation of ngrok’s terms of service.If you are the account owner and believe this is a mistake, please contact support@ngrok.com.
ERR_NGROK_4011Your password must be at least 10 characters.
ERR_NGROK_4013You may not create a new account because you are already a member of a free account. Upgrade or delete that account first before creating a new account.
ERR_NGROK_4100The email or password you entered is not valid.
ERR_NGROK_4101A user with the email address already exists.
ERR_NGROK_4108Sign ups are disallowed for the email provider. Please sign up with a different email provider.
ERR_NGROK_6022Before you can serve HTML content, you must sign up for an ngrok account and install your authtoken.
ERR_NGROK_6024You are about to visit HOSTPORT, served by SERVINGIP. This website is served for free through ngrok.com. You should only visit this website if you trust whoever sent the link to you.
ERR_NGROK_8012Traffic was successfully tunneled to the ngrok agent, but the agent failed to establish a connection to the upstream web service

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All Errors

Consult the Errors Reference Documentation for a complete list of all of ngrok’s error codes.

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Customize Error Pages for your Traffic

To access and provide feedback on a development preview of custom error pages Fill out the form.