What is this JSON formatter?

A formatter, validator, and minifier in one pane: paste JSON and get pretty-printed output with syntax colors, a strict validity check with the exact line and column of the first error, or a compact one-line version for transport. Non-standard input (single quotes, trailing commas, comments, Python-style None/True) is auto-repaired and flagged. Unlike most online formatters, everything runs in your browser: no upload, no storage, zero network requests.

How to use

1. Paste JSON into the Document pane. The formatted result appears in the output pane.
2. Press Format for pretty-printed output or Minify for a compact single line.
3. Press Validate for a strict RFC-8259 check with the precise error line and column.
4. Switch the output to Tree to explore structure, or Query to filter with JSONPath.
5. Copy the result. Your input is never modified.

Examples

{"id":42,"name":"Ada","tags":["json","diff"]}

{
  "id": 42,
  "name": "Ada",
  "tags": [
    "json",
    "diff"
  ]
}

{ 'name': 'Ada', active: True, } // from Python

{
  "name": "Ada",
  "active": true
}

{
  "a": 1,
  "b": 
}

Line 4, col 1: Unexpected token '}', expected a value

Edge cases & gotchas

• JSON requires double quotes: 'single' quotes are invalid, but Format auto-repairs them.
• Trailing commas and comments are not standard JSON (that's JSONC/JSON5); Validate flags them, Format fixes them.
• NaN and Infinity are not valid JSON values.
• Huge numbers lose precision beyond IEEE-754 doubles. Keep 64-bit IDs as strings.
• Duplicate keys are technically parseable but the last one silently wins, a common source of bugs.

FAQ

Related tools

• JSON Compare / Diff
• Sort JSON Keys
• Strip Comments
• JSON Analyzer