Pretty Pretty JSON

Try it live

A single-file, privacy-first JSON prettifier & JWT decoder. Paste unformatted JSON (or a JWT) on the left, get a clean, color-coded, collapsible tree on the right.

Everything happens in your browser. There are no external scripts, fonts, or stylesheets, no network calls, no cookies, and no analytics - the page even ships its own Content-Security-Policy (default-src 'none') so it can't phone home even by accident.

Features

• JSON prettifier - collapsible, color-coded tree plus a plain indented "Raw" view, with clear line/column error messages
• JWT decoder - paste a token to see its decoded header and payload as JSON (decoded locally, signature not verified)

...and a few more worth finding on your own.

Run it locally

Just open public/index.html directly in a browser - double-click it.

No server, no build, no install required. The whole deployable site is the public/ folder - index.html plus a _headers file adding a strict Content-Security-Policy and other hardening headers, for static hosts that support it.

Tests

A Playwright regression suite lives in tests/ and runs against public/index.html directly - no dev server needed.

npm install
npx playwright install chromium   # first time only, downloads the browser
npm test

See tests/README.md for what's covered.

About

I'm Filipe Albero Pomar. Engineering manager, sometime product manager, still hands-on with the code. Curious how? More at alpomar.dev