I recently shipped CutoutKit, a small web app that removes image backgrounds and returns a transparent PNG.
The interface is intentionally simple: upload an image, wait a few seconds, and download the result. The implementation behind that flow was less simple. Once I moved past the prototype, I needed authentication, usage limits, payments, webhook reliability, privacy boundaries, and an architecture that could run comfortably on Cloudflare.
This post covers the decisions and mistakes that were most useful to me. It is not a tutorial for a specific starter repository; it is a set of patterns you can reuse in other API-backed SaaS products.
The constraints shaped the architecture
I started with a few deliberate constraints:
