JSON Formatter & Validator

How JSON formatting works

JSON (JavaScript Object Notation) organizes data as nested key-value pairs. A formatter takes compact JSON — with no line breaks or indentation — and rewrites it with a clear visual hierarchy, so it's easy to read and debug:

// Before
{"user":{"id":42,"name":"Ada","roles":["admin","dev"]}}

// After (2 spaces)
{
  "user": {
    "id": 42,
    "name": "Ada",
    "roles": ["admin", "dev"]
  }
}

This tool uses the browser's native JSON.parse to validate the structure and JSON.stringify to reformat it — no external libraries, no server calls.

Frequently asked questions

Is it safe to paste sensitive data here?

Yes. All processing happens in your browser using native JavaScript; no data is ever sent to a server.

Does it support large JSON files?

It handles most typical JSON files well. Extremely large documents (several MB) can get slow because formatting runs on the main thread.

Does it detect syntax errors?

Yes, it shows the exact line and column where the JSON stops being valid, as soon as you stop typing.

Can I paste multiple JSON documents in a row (NDJSON)?

Yes. If you paste several JSON documents one after another (separated by whitespace or a newline), each one is validated and formatted separately instead of the whole input being marked invalid.