Hermet.dev

Developer tools that never phone home.

Developer tools that never phone home.

Everything runs in your browser — open your Network tab and check. No accounts, no tracking, no uploads, no save button.

JSON FormatterFormat and validate JSON, with plain-language error locations. JSON RepairFix broken JSON — trailing commas, single quotes, truncated AI output. JSON ViewerExplore JSON as a collapsible tree and see the path of any value. JSON to CSVTurn an array of JSON objects into a spreadsheet-ready CSV. JSON to TypeScriptGenerate TypeScript interfaces (or Python dataclasses) from sample JSON. JWT DecoderRead a token's header and claims, and check its expiry. Locally, of course. Base64Encode and decode Base64 with proper UTF-8 handling. URL EncoderPercent-encode text or a full URL, and decode it back. UUID GeneratorBulk-generate version 4 UUIDs from your browser's crypto source. Timestamp ConverterUnix seconds and milliseconds to human dates, and back.

Verify it yourself

  1. Open your browser’s developer tools and go to the Network tab.
  2. Reload this page. The only files loaded come from this site itself — no fonts, no analytics, no third parties.
  3. Use any tool. Zero new requests appear. Your input is processed on this device and nowhere else.
  4. Bonus check: turn on airplane mode after the page loads. Every tool still works.

This page also ships a Content Security Policy of connect-src ’none’ — the browser itself is forbidden from sending your data anywhere, even if the code wanted to. It doesn’t.

Why

Popular formatter sites have been caught exposing what people pasted — production JSON, tokens, keys — through “save” and “share” features, wrapped in hundreds of tracking cookies. Hermet is built the other way: the features that leak were never written.

“Hermetically sealed” is named for the seal of Hermes Trismegistus — Hermes the Thrice-Great. Nothing got in or out then, either.