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