~/tools/json

> json

format and validate json in your browser. pretty-print with 2 or 4 spaces or minify to a single line. syntax errors are shown inline.

indent:

input

$ output

error: empty input

## overview

json (javascript object notation) is the default data interchange format on the web. it is a text-based format for structured data: objects, arrays, strings, numbers, booleans, and null. the spec (rfc 8259) is small enough to fit on a postcard, but valid json has subtle rules: double-quoted keys, no trailing commas, no comments, no single quotes, no unquoted keys. this tool parses json with the browser's built-in json parser, so what passes here is what your javascript will parse. errors include the position of the first mistake. formatting options: 2-space indent (common in code), 4-space indent (legible for data dumps), minified (single line for apis). valid inputs are pretty-printed; invalid inputs show the parser error so you can fix them.

## how to use

paste your json — paste anywhere. the tool parses as you type.
choose indentation — pick 2 spaces, 4 spaces, or minified. this affects the output only, not validation.
read the error if any — if the input is invalid, the error shows the problem and often the character offset.
copy the output — copy the formatted text for use in a file, test fixture, or api request body.

## examples

$ example 1 — pretty-printed with 2-space indent

$ in
{"a":1,"b":[1,2,3]}

# out
{
  "a": 1,
  "b": [
    1,
    2,
    3
  ]
}

$ example 2 — invalid

$ in
{a:1}

# out
error: unexpected token a — keys must be double-quoted strings

$ example 3 — trailing comma

$ in
{"a":1,}

# out
error: unexpected token } — trailing commas are invalid in json

## common mistakes

trailing commas — valid in javascript, invalid in json. remove any comma before `]` or `}`.
single quotes — json requires double quotes around strings and keys. `'a'` is invalid.
comments — json has no comments. `//` and `/* */` will fail to parse. if you need comments, use jsonc (a json superset) — but only tools that explicitly support it will parse it.
number edge cases — json numbers cannot be NaN, Infinity, or have leading zeros. `-.5` is invalid; use `-0.5`. very large integers lose precision beyond 2^53.
duplicate keys — json technically allows duplicate keys; behaviour depends on the parser. some take the first, some the last. avoid them.

## faq

does this send my json anywhere?

no. parsing runs in your browser via `JSON.parse` and `JSON.stringify`.

what is the size limit?

limited by your browser's string memory and the textarea. roughly a few megabytes is fine; gigabytes are not.

why does my json say 'unexpected token'?

usually a quote, comma, or bracket mismatch. the parser will point at the first problem, but the real mistake is often just before.

can i preserve key order?

yes. JSON.parse and JSON.stringify preserve insertion order per the spec.

does minified json save much?

minified removes whitespace. for typical api payloads, expect 5-30% size reduction.

what about jsonc or json5?

this tool parses strict json (rfc 8259). for jsonc (with comments) or json5 (relaxed syntax), remove those features first or use a dedicated parser.

why do my numbers round?

javascript numbers are ieee 754 doubles; integers above 2^53 − 1 lose precision. if you need exact big integers in json, encode them as strings.

## related tools

base64 — encode and decode base64 strings (client-side, unicode-safe).
url codec — percent-encode and decode URL components.

## references

ad slot · tool-json