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. The main constraint I set for myself was to use zero dependencies, no server, and no telemetry. When using Antigravity Tools, every operation runs inside your browser using native APIs, ensuring your data stays private and secure.

The 8 tool categories include:

🔐 Security & Auth Tools: JWT Inspector for decoding JWT headers, payloads, and checking expiry; RSA & ECC Key Generator for generating 2048-bit key pairs; Hash & Password Generator using SHA-256/SHA-512; PII Masker for stripping emails, credit cards, SSNs, and IPs from text; Universal Encoder/Decoder for Base64, URL, Hex, HTML entities, and Unicode encoding.

🤖 AI & Prompting Tools: AI Token Counter to estimate cost across GPT-4o, Claude 3.5, Gemini 2.0, and DeepSeek; System Prompt Builder to structure agent instructions with XML tags and tool definitions; AI Text Humanizer to rephrase robotic AI output into natural writing; Prompt Cost Trimmer to compress prompts by 30-50% to reduce API costs.

⚡ Dev & Code Tools: JSON Workbench to beautify, validate, and convert to TypeScript, Python, or Go types; cURL Converter to convert cURL commands to JavaScript fetch, Python requests, Go, or PHP; Regex Tester for real-time match highlighting with capture group display; Cron Builder, a visual cron expression editor with plain-English output; Git Command Helper for building undo, squash, and cherry-pick commands visually.