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Workers
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  1. Products
  2. Workers
  3. Observability
  4. Errors and exceptions

Errors and exceptions

Review Workers errors and exceptions.

​​ Error pages generated by Workers

When a Worker running in production has an error that prevents it from returning a response, the client will receive an error page with an error code, defined as follows:

Error code Meaning
1101 Worker threw a JavaScript exception.
1102 Worker exceeded CPU time limit.
1015 Worker hit the burst rate limit.
1019 Worker hit loop limit.
1021 Worker has requested a host it cannot access.
1022 Cloudflare has failed to route the request to the Worker.
1024 Worker cannot make a subrequest to a Cloudflare-owned IP address.
1027 Worker exceeded free tier daily request limit.
1042 Worker tried to fetch from another Worker on the same zone, which is unsupported.

Other 11xx errors generally indicate a problem with the Workers runtime itself. Refer to the status page if you are experiencing an error.

​​ Loop limit

A Worker cannot call itself or another Worker more than 16 times. In order to prevent infinite loops between Workers, the CF-EW-Via header’s value is an integer that indicates how many invocations are left. Every time a Worker is invoked, the integer will decrement by 1. If the count reaches zero, a 1019 error is returned.

​​ Errors on Worker upload

These errors occur when a Worker is uploaded or modified.

Error code Meaning
10006 Could not parse script body.
10007 Script or workers.dev subdomain not found.
10015 Account is not entitled to use Workers.
10016 Invalid script name.
10026 Could not parse request body.
10035 Multiple attempts to modify a resource at the same time
10037 An account has exceeded the number of Workers scripts allowed.
10026 Could not parse request body.
10052 A binding is uploaded without a name.
10054 A environment variable or secret exceeds the size limit.
10055 The number of environment variables or secrets exceeds the limit/Worker.
10056 Binding not found.
10068 The uploaded script has no registered event handlers.
10069 The uploaded script contains event handlers unsupported by the Workers runtime.

​​ Runtime errors

Runtime errors will occur within the runtime, do not throw up an error page, and are not visible to the end user. Runtime errors are detected by the user with logs.

Error message Meaning
Network connection lost Connection failure. Catch a fetch or binding invocation and retry it.
Memory limit
would be exceeded
before EOF		 Trying to read a stream or buffer that would take you over the memory limit.
daemonDown A temporary problem invoking the Worker.

​​ Identify errors: Workers Metrics

To review whether your application is experiencing any downtime or returning any errors:

  1. Log in to the Cloudflare dashboard and select your account.
  2. In Account Home, select Workers & Pages.
  3. In Overview, select your Worker and review your Worker’s metrics.

​​ Debug exceptions

After you have identified your Workers application is returning exceptions, use wrangler tail to inspect and fix the exceptions.

Exceptions will show up under the exceptions field in the JSON returned by wrangler tail. After you have identified the exception that is causing errors, redeploy your code with a fix, and continue tailing the logs to confirm that it is fixed.

​​ Set up a logging service

A Worker can make HTTP requests to any HTTP service on the public Internet. You can use a service like Sentry to collect error logs from your Worker, by making an HTTP request to the service to report the error. Refer to your service’s API documentation for details on what kind of request to make.

When using an external logging strategy, remember that outstanding asynchronous tasks are canceled as soon as a Worker finishes sending its main response body to the client. To ensure that a logging subrequest completes, pass the request promise to event.waitUntil() . For example:

​​ Go to origin on error

By using event.passThroughOnException, a Workers application will forward requests to your origin if an exception is thrown during the Worker’s execution. This allows you to add logging, tracking, or other features with Workers, without degrading your application’s functionality.

  • Log from Workers - Learn how to log your Workers.
  • Logpush - Learn how to push Workers Trace Event Logs to supported destinations.