Online JSON Formatter: Pretty-Print, Validate & Minify JSON Instantly
Every developer hits the same wall: an API returns a wall of minified JSON, or a config file fails to parse and you can't see where. An online JSON formatter fixes both — pretty-print for readability, validate to catch errors, and minify to shrink payloads. The good ones run entirely in your browser, so your data never touches a server.
What a JSON formatter does
- Pretty-print — turn minified JSON into readable, indented output
- Validate — instantly find missing commas, quotes, or brackets
- Minify — compress JSON for storage and API payloads
- Error location — see exactly where the parser choked
Format JSON online with Tooly
The Tooly JSON Formatter covers all of it:
- Paste any JSON → pretty-printed instantly, with syntax highlighting
- Validation errors reported with line context, so you fix them fast
- One-click minify for production payloads
- 100% client-side — your data never leaves your browser
Open JSON Formatter
Common JSON errors (and how to spot them)
| Error | Fix |
|---|---|
| Missing comma between objects | Add , after the closing brace |
| Trailing comma in arrays/objects | Remove the last comma before ] or } |
| Single quotes instead of double | JSON requires double quotes: "key": "value" |
| Unquoted keys | Every key must be wrapped in quotes |
| Comments in JSON | JSON doesn't allow comments — strip them (use JSONC for configs) |
When you'll reach for it
- Debugging API responses from curl or Postman
- Cleaning up config files before deployment
- Preparing data for CSV/JSON conversions (see CSV to JSON)
- Shrinking payloads for storage or transfer (minify)
Frequently Asked Questions
Is this JSON formatter really free? Yes — unlimited use, no account, no watermark, no limits.
Is my JSON uploaded? No — formatting and validation run entirely in your browser, so sensitive data stays on your device.
Does it handle large JSON files? Yes — it processes in-browser with fast validation, ideal for API dumps and configs.
Can it convert JSON to CSV? Use the dedicated JSON to CSV tool for that.