Hermet.dev Pro

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 for the tools, 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 or markdown-wrapped 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.

Only two pages ever talk to a server: the Account page, for sign-in and your plan, and the Pro checkout, where payment is handled by Paddle. No tool page can — the policy above forbids it.

Each tool page also counts for you while you work: a line at the top reads “Network requests while you work: 0”, and it stays at zero.

Why

Popular formatter sites let anyone read what people had saved. In November 2025, watchTowr Labs pulled 80,000+ saved pastes from two of them — production JSON, passwords, tokens, keys — because their “save” and “share” links were public, listed for anyone to browse, on pages that fire more than 500 requests to third parties in a single visit. 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.

Hermet Pro

The tools above are free, and stay free. Pro adds batch processing, large files that never freeze the page, saved workspaces on your own device, and the installable offline app. $5/month or $39/year.