Free AI Image Generation API

I wanted images from scripts, apps and automations without running a GPU server or signing up for a per-image API. Cloudflare already runs image models next to its Workers, so the missing piece was a small, private endpoint in front of them.

One Cloudflare Worker, 51 lines of JavaScript, that you deploy on your own Cloudflare account. You send it a prompt with your key and it answers with an image. There is no shared public endpoint: this page shows you how to run your own copy, and it runs inside your account's own Workers AI allowance.

How it works

Every request passes three checks before any model runs. The Authorization header must equal Bearer <API_KEY>, compared with a variable on your Worker; anything else gets 401. Only POST to / is allowed (405 otherwise), and the JSON body needs a prompt (400 if it is missing). Then the Worker calls the model through the AI binding and returns the result as the response body:

            const result = await env.AI.run(
                "@cf/stabilityai/stable-diffusion-xl-base-1.0",
                { prompt }
            );

            return new Response(result, {
                headers: { "Content-Type": "image/jpeg" },
            });

Full file: worker.js. Only the prompt is passed; there are no size, seed or step options. Nothing is stored, and there is no rate limiting or logging in the Worker, so treat the key as the only gate.

To deploy your own:

1. In the Cloudflare dashboard, create a Worker and paste worker.js into it.
2. Add API_KEY with a long random value, ideally as an encrypted secret.
3. Add a Workers AI binding named AI.
4. Deploy, then call your Worker's URL with curl or fetch, the bearer header and {"prompt": "..."}.

Set the key before you share the URL with anything. If API_KEY is unset, the Worker compares the header with the literal string Bearer undefined, so a request sending exactly that would get through.

Status and links

Self-host only: there is no public endpoint to call, and I don't quote a free-tier number because Cloudflare's allowances change; check your own account's Workers AI limits. The code is on GitHub (link above). It has no tests or CI yet, and the other model IDs listed in a code comment are not drop-in swaps: most return a different format or need an input image.