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 my indexable pages without building a single new tool. The Italian version of text repeater ranks on page 1 of Google — the English version doesn't even appear.
3. JSON-LD structured data is free SEO
Adding FAQPage, HowTo, and WebApplication schemas helped Google understand what each page does. It's a few lines of code for potentially better search snippets.
Tools That Developers Will Actually Use
Here are some that I use daily myself:
- JSON Formatter — paste, format, done
- Regex Tester — real-time matching with explanation
- SQL Formatter — cleans up messy queries
- YAML Formatter — validates and prettifies
- Base64 Converter — encode/decode instantly
- Hash Generator — MD5, SHA-1, SHA-256
- Color Palette Generator — for quick UI work
- Cron Expression Generator — never Google cron syntax again
Privacy First
Every tool runs 100% client-side. No analytics cookies (we use consent-based GA4), no server processing, no data storage. Your files and data never leave your browser.
What's Next
I'm aiming for 200 tools by Q2 2026. The site is open and free — if you have ideas for tools you'd find useful, drop a comment!
Check it out: toolkitonline.vip
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