Building a Free Invoice Generator with Zero Backend Cost

The Problem Every freelancer needs invoices. Most "free" tools aren't really free — they limit you to 5 invoices/month, require an account, or add watermarks. I wanted to build the simplest possible invoice tool with zero ongoing costs. The Architecture The entire application runs client-side in the browser: No backend — all logic runs in JavaScript No database — form state lives in the DOM No auth — no accounts to manage No server costs — Firebase Hosting free tier handles everything Key Techni