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

I have been quietly developing Antigravity Tools, a collection of 59 free, browser-based developer utilities. Today, I am sharing everything that was built and the lessons learned in the process. The main constraint set for this project was to use no dependencies, no server, and no telemetry. When you input your JWT token into jwt.io, the data is sent to their server.

Similarly, when using an online regex tester, your test strings are logged. Antigravity Tools ensures that every operation runs inside your browser using native APIs, including Web Crypto API, Canvas API, Web Audio API, and IndexedDB.

The project comprises eight tool categories:

- Security & Auth Tools: JWT Inspector, which decodes JWT header, payload, and checks expiry locally; RSA & ECC Key Generator, allowing the generation of 2048-bit key pairs via SubtleCrypto; Hash & Password Generator, utilizing SHA-256/SHA-512 via Web Crypto; PII Masker, which strips emails, credit cards, SSNs, IPs from text; and Universal Encoder/Decoder, supporting Base64, URL, Hex, HTML entities, and Unicode.

- AI & Prompting Tools: AI Token Counter, estimating costs across GPT-4o, Claude 3.5, Gemini 2.0, and DeepSeek R1; System Prompt Builder, structuring agent instructions with XML tags and tool definitions; AI Text Humanizer, rephrasing robotic AI output into natural writing; and Prompt Cost Trimmer, compressing prompts by 30–50% to reduce API costs.

- Dev & Code Tools: JSON Workbench, which beautifies, validates, and converts data to TypeScript, Python, Go types; cURL Converter, converting cURL to JS fetch, Python requests, Go, and PHP; Regex Tester, offering real-time match highlighting with capture group display; Cron Builder, a visual editor for cron expressions with plain-English output; and Git Command Helper, enabling the creation of undo/squash/cherry-pick commands visually.

To explore Antigravity Tools, visit https://antigravitytools.app.