I built 59 free browser-based dev tools in vanilla JS — here's what I learned

I've been quietly building Antigravity Tools — a collection of 59 free, browser-based developer utilities — and today I'm sharing everything I built and learned. Why vanilla JS? No React, no build step. The main constraint I set for myself: zero dependencies, zero server, zero telemetry . When you paste your JWT token into jwt.io, it goes to their server. When you use an online regex tester, your test strings are logged. I built Antigravity Tools so every operation runs inside your browser, using native APIs. No Node.js backend No npm packages No webpack/vite/parcel No Google Analytics No cookies Everything runs on Web Crypto API , Canvas API , Web Audio API , and IndexedDB — all native to modern browsers. The 8 tool categories 🔐 Security & Auth Tools JWT Inspector — decode JWT header, payload, and check expiry locally RSA & ECC Key Generator — generate 2048-bit key pairs via SubtleCrypto Hash & Password Generator — SHA-256/SHA-512 via Web Crypto PII Masker — strip emails, credit cards, SSNs, IPs from text Universal Encoder/Decoder — Base64, URL, Hex, HTML entities, Unicode 🤖 AI & Prompting Tools AI Token Counter — estimate cost across GPT-4o, Claude 3.5, Gemini 2.0, DeepSeek R1 System Prompt Builder — structure agent instructions with XML tags and tool definitions AI Text Humanizer — rephrase robotic AI output into natural writing Prompt Cost Trimmer — compress prompts by 30–50% to reduce API costs ⚡ Dev & Code Tools JSON Workbench — beautify, validate, convert to TypeScript, Python, Go types cURL Converter — cURL → JS fetch, Python requests, Go, PHP Regex Tester — real-time match highlighting with capture group display Cron Builder — visual cron expression editor with plain-English output Git Command Helper — build undo/squash/cherry-pick commands visually Try it 👉 https://antigravitytools.app