JSON formatter and validator

The text is parsed as you type (big inputs after a short pause). Valid JSON is printed again with the indentation you pick: 2 spaces, 4 spaces or tabs, or no whitespace at all in Minify mode. Sort keys orders every object's keys the way jq -S and Python's sort_keys do, which makes two JSON files easy to compare in a diff.

Unlike formatters built on JSON.parse, it never converts your values. Numbers and string escapes are printed exactly as written, so a 19-digit ID or 1.50 comes out unchanged. It also warns about things that are valid but risky: duplicate keys, integers too big for JavaScript, and a whole document that is a string with escaped JSON inside (common in logs), which you can unescape with one click.

Input can come from the clipboard, a dropped or opened .json file, or a public URL (load URL). Big files stay usable: parsing waits for a short pause in typing, the tree shows long arrays 200 items at a time, and the size, key count, depth and value counts update with every change.

The Tree view collapses objects and arrays and shows how many keys or items each one holds. Search finds keys and values, and clicking a row copies its path as JSONPath ($.orders[0].total), with buttons for the JavaScript accessor and JSON Pointer (/orders/0/total). To query a document with JSONPath expressions, use the JSONPath tester.

JSON is stricter than the JavaScript it came from. RFC 8259 allows only double-quoted strings, no comments, no trailing commas, and the values true, false and null. These are the mistakes that break most JSON, and all of them are fixed by Repair JSON:

Repair also handles Python True/False/None (from printing a dict), curly quotes pasted from a document, hex numbers, a JSONP callback(...) wrapper and missing closing brackets at the end of a cut-off response. It lists every change it made, and Undo brings back your input.

JavaScript: the third argument of JSON.stringify is the indent, a number of spaces (up to 10) or a string such as a tab.

const pretty = JSON.stringify(data, null, 2);
const minified = JSON.stringify(data);
const fromText = JSON.stringify(JSON.parse(text), null, '\t');

Python: json.dumps takes indent and sort_keys. Pass ensure_ascii=False to keep non-ASCII characters instead of \u00e9 escapes. From a shell, python -m json.tool formats a file.

import json
print(json.dumps(data, indent=2, sort_keys=True, ensure_ascii=False))

# shell
python -m json.tool data.json
python -m json.tool --sort-keys --indent 4 data.json

jq: . pretty-prints, -c minifies, -S sorts keys and --tab or --indent n sets the indentation.

jq . data.json
curl -s https://api.example.com/users | jq .
jq -c . data.json        # minify
jq -S --indent 4 . data.json

Go: json.MarshalIndent encodes a value with indentation, and json.Indent reformats JSON bytes you already have.

out, err := json.MarshalIndent(v, "", "  ")

var buf bytes.Buffer
err = json.Indent(&buf, raw, "", "  ")

Config files often use relaxed JSON dialects. Turn on Allow comments (JSONC) above to format them without errors. In that mode comments are kept when formatting; minifying or sorting keys drops them.

A JSON parser rejects anything in the JSONC or JSON5 columns. To turn such a file into strict JSON, press Repair JSON. To move between JSON and YAML, use the JSON to YAML converter.

JSON itself puts no limit on numbers, but RFC 8259 notes that software commonly stores them as IEEE 754 double-precision floats, which hold integers exactly only up to 2⁵³ - 1 (9007199254740991, Number.MAX_SAFE_INTEGER in JavaScript). Anything larger is rounded by JSON.parse:

JSON.parse('{"id": 1851234567890123456}').id
// 1851234567890123500

That is why many APIs send large IDs as strings. This formatter keeps the original digits and flags each number that would be rounded, with its path. In your own code, ask the API for string IDs, or parse with a library that supports BigInt.

Convert an array of objects to a spreadsheet with JSON to CSV, generate types with JSON to TypeScript, or compare two documents in the diff checker (format both with sorted keys first). Building on an API? Browse API tools on DevHunt.