JSON Formatter & Validator

How it works

The text is parsed with your browser's built-in JSON parser and written back out. If parsing fails, nothing is output and the parser's own error message is shown. If it succeeds, Pretty-print indents with two spaces and Minify removes all spacing. Both keep the data identical.

Example

The input {"a":1,"b":[true,null]} pretty-prints to:

{
  "a": 1,
  "b": [
    true,
    null
  ]
}

What re-writing can change

• Strict JSON only: comments, trailing commas and single quotes are rejected rather than repaired.
• If an object repeats a key, only the last value survives.
• Integers beyond 9,007,199,254,740,991 lose precision, because the parser reads numbers as JavaScript numbers.
• Error wording differs a little between browsers, so the same mistake may be described differently.

Pretty-print vs. minify

Pretty-printing adds indentation and line breaks to make JSON readable for humans. Minifying strips all unnecessary whitespace to make the file as small as possible — useful when sending JSON over a network where every byte counts, but hard to read.

Handy ways to use the output

Pretty-print before comparing two versions of a file line by line, for example in the Text Diff Checker, because both copies then use the same layout. Minify before pasting JSON into a single-line field such as a config value or a URL parameter.

Common JSON mistakes this catches

• Trailing commas after the last item in an object or array
• Using single quotes instead of double quotes for strings
• Missing a closing brace, bracket, or quote
• Unquoted object keys

Edge cases, with real input

Pretty-print and Minify both parse the text and write it back out, so they show what a program would actually read. Minify turns { "a" : 1 , "b" : [ true , null ] } into {"a":1,"b":[true,null]}. Numbers are rewritten as numbers, so [1.0, 1e3, 0.10] becomes [1,1000,0.1]. Empty containers stay compact, and {"a":{}} pretty-prints as an object holding an empty object on one line.

Three results surprise people. A repeated key keeps only its last value, so {"a":1,"a":2} becomes {"a":2}. A key that looks like a whole number moves to the front of its object, so {"b":1,"2":2,"1":3} comes out as {"1":3,"2":2,"b":1}, because that is how JavaScript orders object keys. And 12345678901234567890 is written back as 12345678901234567000, since the last digits cannot be held exactly; keep IDs that long as strings.

A missing quote, an unquoted key or a trailing comma is reported with your browser's own wording and, in current browsers, a line and column position. Fix the first reported problem and format again, since later ones are often caused by it.