I've been building SnapAPI — a tool that turns JSON into REST APIs instantly — and along the way I built some standalone JSON utilities that I use daily. They're all free, no signup, and work right in your browser.
1. JSON Formatter
Paste messy JSON, get it beautifully formatted. Also has a minify button for when you need compact JSON.
I use this dozens of times a day when debugging API responses.
2. JSON Validator
Real-time validation as you type. Shows you exactly where the syntax error is, plus structural info (number of keys, array lengths, nesting depth).
3. JSON to TypeScript
Paste an API response, get TypeScript interfaces. Handles nested objects, arrays, and mixed types. Saves me from writing interfaces by hand.
4. Fake Data Generator
Define fields and types, get realistic mock data instantly. Supports names, emails, numbers, dates, UUIDs, and more.
Perfect for:
- Seeding a database
- Testing UI components
- Creating demo data
Bonus: Turn your JSON into a live API
This is what SnapAPI was actually built for. Drop any JSON and get a fully functional REST API with CRUD operations in 5 seconds:
curl -X POST https://snapapi.akokoa1221.workers.dev/api/mock \
-H "Content-Type: application/json" \
-d '{"users": [{"id": 1, "name": "Alice"}]}'
No signup, CORS enabled, auto data generation, delay simulation — all free.
All tools are open source: github.com/ko-tarou/snapapi
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