JSON Formatter & Validator

What is JSON?

JSON (JavaScript Object Notation) is the plain-text format most APIs, config files and web apps use to exchange structured data — nested key-value pairs, lists and text, without any binary format or schema required. It's standardized in RFC 8259. When JSON comes back from an API compressed onto a single line, or has a typo that breaks it, this tool re-indents it for readability, tells you exactly where a syntax error is, and can shrink it back down (minify) for production use.

How to use JSON Formatter

1. Paste your JSON into the Input panel, or click Paste / Example.
2. Any syntax error is flagged immediately with the exact line and column.
3. Pick 2 sp., 4 sp. or Minified above the Output panel to control the output style.
4. Click Copy or Download to grab the formatted result.

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 — both implement the grammar defined in RFC 8259, so parsing behavior (rejecting trailing commas, requiring double-quoted keys, etc.) matches the spec exactly, not a looser JSON5/JSONC dialect. 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.