my-image-resizer – Image optimizer (Cloudflare Workers)

Resize images on the fly via a single URL. The worker fetches the origin image, scales it to the requested width (aspect ratio preserved), and serves it with long-lived cache headers.

Usage

https://myworker.<your-subdomain>.workers.dev/<width>/<full-image-url>

Examples

• https://myworker.xxx/500/https://example.com/photo.jpg → image scaled to 500px width
• https://myworker.xxx/1200/https://cdn.example.com/assets/hero.png → 1200px width

Width must be between 1 and 4096. The image is scaled down to that width (never upscaled) and aspect ratio is preserved. Format is chosen automatically (e.g. WebP/AVIF when the client supports it).

If the image URL contains special characters, encode it (e.g. https%3A%2F%2Fexample.com%2Fpath%2Fimage.jpg).

Setup

1. Install dependencies

   npm install

2. Create your local Wrangler config

   cp packages/backend/wrangler.toml.example packages/backend/wrangler.toml

   Then edit packages/backend/wrangler.toml and set your worker name.

3. Deploy

   cd packages/backend && npm run deploy

4. Enable Image Resizing on your zone

   Image transformation is done by Cloudflare’s Image Resizing. You need it enabled for the zone the worker runs on:

   • In the Cloudflare dashboard, open your account and the zone that will receive the traffic (e.g. the zone for your workers.dev subdomain, or your custom domain).
   • Go to Speed → Optimization.
   • Turn Image Resizing ON.

   If Image Resizing is not enabled, the worker will still run but images will be returned at original size.

   Important: Resizing only runs when the worker is hit via a custom domain attached to a zone that has Image Resizing ON. The default *.workers.dev URL does not use your zone, so images there are served at original size. Add a custom domain (e.g. img.yourdomain.com) in Workers & Pages → your worker → Settings → Domains, then enable Image Resizing for that zone in Speed → Optimization.

Local dev

npm run backend

Opens http://localhost:8777. Image Resizing is not applied in local mode — you get the original image. To test resizing locally, run the worker on Cloudflare’s network:

cd packages/backend && npm run dev:remote

Then hit the same URL; images will be resized. Or deploy and test on your live worker URL.

Project layout

• packages/backend/src/index.ts - Worker entrypoint.
• packages/backend/wrangler.toml.example - Starter config; copy to wrangler.toml locally.