I Built a Privacy-First Zakat Calculator with React—Here's What I Learned

A few months ago, I built a Zakat calculator for my family. It was supposed to be a weekend project. It turned into a lesson in privacy, performance, and what "free" actually costs. The stack: React, Vite, Tailwind CSS, hosted on Netlify. The twist: I decided early that this would be completely privacy-focused. No backend. No database. No analytics. No email capture. Here's what that decision taught me. Why Privacy-First Architecture Matters Most Islamic finance apps I tested required: Email signup Phone number verification Account creation just to calculate a number Your Zakat calculation reveals your complete financial picture—bank balances, investments, gold holdings, debts. That's sensitive data. I didn't want to store that. Ever. Technical approach: 100% client-side JavaScript localStorage for temporary calculation state (clears on page close) No API calls after initial page load No cookies, no tracking pixels, no Google Analytics Trade-off? I can't "improve the product"