Resend on Cloudflare Workers: needs a bundling setup, and the key comes from env, not source

Workers: bundling prerequisite, env key, handler-scoped client

Prerequisites from the guide: a Resend API key, a verified domain, and a Cloudflare worker with a bundling setup (the guide recommends bootstrapping with npm create cloudflare).

import { Resend } from 'resend';

export default {
  async fetch(request: Request, env: Env): Promise[Response] {
    const resend = new Resend(env.RESEND_API_KEY);
    const { data, error } = await resend.emails.send({
      from: '[SENDER]',
      to: ['[RECIPIENT]'],
      subject: 'Hello World',
      html: '<strong>It works!</strong>',
    });
    if (error) {
      return Response.json({ error }, { status: 400 });
    }
    return Response.json({ id: data.id });
  },
};

Checklist

• The guide writes new Resend('re_xxxxxxxxx'). That is a placeholder. Bind the real key as a worker secret and read it from env. A literal in source ends up in the bundle and in version control.

• Construct the client inside fetch where env is available. Module scope has no access to the worker environment.

• Keep the bundling setup the guide asks for. The SDK is an npm package; a worker without a bundler cannot import it.

Resend's Cloudflare Workers guide lists the bundling setup prerequisite and builds the send inside the fetch handler. Verified live at https://resend.com/docs/send-with-cloudflare-workers.