Cloudflare Workers "Script startup exceeded CPU time limit" in CI

When a Worker is uploaded, Cloudflare runs its top-level code once to validate it. If that startup work exceeds the CPU budget, the deploy is rejected with "Script startup exceeded CPU time limit".

What this error means

A wrangler deploy step fails with "Script startup exceeded CPU time limit." and the Worker is not published.

Wrangler

✘ [ERROR] A request to the Cloudflare API failed.
  Script startup exceeded CPU time limit.

Common causes

Heavy work at module top level

Parsing large data, building big structures, or running expensive setup as the module loads consumes the startup CPU budget.

A large or unoptimized bundle

A big bundle takes longer to parse and initialize, which counts toward the startup limit measured during validation.

How to fix it

Defer initialization to the first request

Identify top-level work that runs as the module loads.
Move it into the fetch handler and memoize so it runs once per isolate.
Redeploy and confirm validation passes.

src/index.js

let cache;
export default {
  async fetch(req, env) {
    cache ??= await loadConfig(env);
    return respond(req, cache);
  }
};

Shrink the bundle

Remove large dependencies and split heavy data out of the bundle so startup parsing stays within budget.

How to prevent it

Keep top-level module code light; defer setup to the handler.
Avoid embedding large data blobs in the bundle.
Profile the bundle size before deploying.