Working with JSON every day, I found myself constantly switching between browser tabs to format messy payloads from APIs. Every tool I used either had ads everywhere, required signup, or sent my data to a server. So I built my own.

jsonproject.com — a free, browser-only JSON formatter, validator, and auto-fixer. No ads, no signup, no data ever leaves your machine.

What it does

Format & pretty-print — 2, 3, 4 spaces, tabs, or compact mode

Validate against RFC 8259 with inline error markers

Minify for production payloads

Auto-fix broken JSON — trailing commas, single quotes, unquoted keys

Fetch JSON from a URL — paste an API endpoint and format the response instantly

Drag-and-drop file upload

Format history — last 20 operations saved in session

Dark mode

Monaco Editor — same editor as VS Code, with full syntax highlighting

Tech stack

Angular 21 with SSR and prerendering

Monaco Editor via ngx-monaco-editor-v2

Tailwind CSS for styling

TypeScript throughout

The interesting parts

Monaco Editor in…