I Built 155+ Free Browser Tools — Here's What I Learned

Last year I started a side project: build a collection of free online tools that work entirely in the browser — no signups, no server processing, no data collection. Today ToolKit Online has over 155 tools across 7 categories, available in 6 languages. Here's what I learned building it. The Stack Next.js 16 with App Router TypeScript + Tailwind CSS Vercel for hosting (free tier) Static generation for all pages (~960 pages) Every tool is a single page.tsx with 'use client' — no backend needed. All processing happens in the browser using Web APIs: Canvas for image tools, Web Audio for sound tools, Clipboard API for text tools. What Surprised Me 1. Finance tools get the most traffic I expected developer tools to perform best (JSON formatters, regex testers). Wrong. Finance calculators like the fuel cost calculator and VAT calculator get the most Google impressions by far. 2. Localization matters more than you think Adding Italian, Spanish, French, German, and Portuguese translations 6x'd