How I built a calculator site with 13 languages and 5,500 static pages in Next.js 15

A few months back I got frustrated. I needed to calculate something — nothing crazy, just a loan payment — and every site I landed on either wanted me to sign up, showed ads on every input, or was in English only (not helpful when sharing with family abroad). So I built Calculora . It's a free calculator site. 150+ tools, 13 languages, zero data collection. Everything runs in your browser — nothing gets sent anywhere. Why 13 languages? Because most people on the internet don't speak English as a first language. I wanted it to actually work for them — not just have a translated homepage, but real localized URLs, right-to-left layout for Arabic, the whole thing. Getting that right in Next.js took more time than I expected. Each tool has a different slug per language, so the routing has to map hundreds of combinations correctly. Totally worth it though. The math rendering For tools like the equation solver and statistics calculator, I wanted the formulas to look like real math — not just text. I used KaTeX for this. It's fast, lightweight, and renders LaTeX properly in the browser. The step-by-step solutions actually show the working — discriminant, roots, the full process — rendered cleanly. Some tools I'm proud of Equation Solver — linear and quadratic, with full steps shown Statistics Calculator — mean, median, mode, IQR, std dev, exportable FIRE Calculator — retirement planning done simply Debt Snowball/Avalanche — side-by-side payoff comparison What's next More tools, better mobile experience, and filling in gaps across the language versions. If you try it, I'd genuinely love feedback — especially on anything that feels off or missing. calculora.net