Cloudflare Workers error codes
Each error code explained with causes, symptoms, fixes, and how to capture it with a Tail Worker.
Worker threw exception
Cloudflare Error 1101 means your Worker threw an uncaught exception during request handling. The request fails with a 500 response, and if you're using Sentry or console.log-based logging, you likely see nothing — the crash happened too fast for your SDK to fire.
Worker exceeded memory limit
Cloudflare Error 1027 means your Worker exceeded the 128MB memory limit. The runtime kills the Worker immediately — no graceful shutdown, no SDK call, no error handler. This is one of the hardest crashes to debug because your code never gets a chance to log what happened.
Bad WebSocket upgrade
Cloudflare Error 1042 means a WebSocket upgrade request failed. This typically happens when your Worker doesn't properly handle the WebSocket upgrade headers, or when a Durable Object's WebSocket hibernation API is misconfigured.