CORS Errors in AI-Generated Apps

What is CORS and why does it appear?

CORS (Cross-Origin Resource Sharing) is a browser security mechanism. When a frontend on one domain tries to talk to a backend on another, the browser blocks the request — unless the server explicitly allows it.

On localhost this isn't an issue because frontend and backend share the same origin. After deployment — when the frontend lives on app.example.com and the API on api.example.com — the browser starts blocking requests. Common scenario: the app passes all local tests, then nothing works in production.

CORS itself isn't hard to fix. It's a few headers on the server. The problem starts when you ask AI to help.

How to fix CORS without breaking your app

1. Don't let AI edit server code. A CORS error is a configuration problem, not a business logic issue. Restrict AI to the frontend — let it fix requests, headers, and URLs on the client side only.
2. Centralize CORS in a single helper. Instead of adding headers to every function separately, create a small module at the server boundary that handles CORS for all endpoints. One change, one place.
3. Keep the entry file tiny. Your main Edge Function file should import modules and delegate work. Real logic lives in separate files. This way, AI won't rewrite your entire logic when trying to add a header.
4. Lock the response JSON shape. Define a clear contract: which fields the API returns, in what format. If AI changes the response shape, the frontend breaks immediately — and you'll see it right away.
5. Query only real columns. Don't put comments inside select() strings. The database doesn't understand SQL comments in a JavaScript string — it silently returns null instead of data.
6. Add structured logs and a quick self-test. A simple health endpoint (/health) plus structured logs on every request will catch regressions before they reach users.