Cloudflare Error 1101: Worker Threw an Exception

Symptom

A page served by a Worker returns "Error 1101: Worker threw an exception".

Root cause

Uncaught JavaScript exception inside the Worker code path.

Fix, in order

1. Stream live Worker logsnpx wrangler tail <worker-name>
2. Look for the throw site in the tail outputfilter: --format pretty
3. Wrap risky boundaries (fetch, JSON.parse) in try/catch and log contexttry { JSON.parse(body) } catch (e) { return new Response("bad json", {status: 400}) }

Prevent it coming back

Deploy with wrangler tail running; never trust external API shapes without guards.

Deep-dive article

Full walkthrough: Cloudflare Error 1101: Worker Threw an Exception on the NinjaOps blog.

Run it on clean infra

Spinning up a fresh box to reproduce or escape this error?

Build apps without servers

Related

Cloud & DevOps tool comparisons · Hardware build guides

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Last reviewed 2026-10-02 · NinjaOps SEO grid · DevOps blog