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JSON Formatter

A JSON formatter turns compact or messy JSON into indented, readable text, and a validator checks that it follows the JSON syntax rules. This tool does both as you type: it parses your input with the browser's standard JSON parser, reports any syntax error, and outputs either pretty-printed JSON with 2-space indentation or a minified single line.

Updated Free, no sign-up, runs in your browserHow we check formulas

Output
Indent

Valid JSON

{
  "tool": "mortgage",
  "inputs": {
    "price": 425000,
    "down": 0.2,
    "rate": 6.4
  },
  "saved": true,
  "tags": [
    "home",
    "loan"
  ]
}

How to use the JSON Formatter

  1. Paste or type JSON in the JSON box.
  2. Check the status line: it says Valid JSON or shows the parser's error message.
  3. Choose Format for indented output or Minify for a single compact line.
  4. Press Copy to put the result on your clipboard.

Formula

JSON.parse(input) → JSON.stringify(value, null, 2) for Format, JSON.stringify(value) for Minify

Validation uses the browser's built-in JSON parser, which follows the JSON standard (RFC 8259). Formatting re-serializes the parsed value, so the data and key order stay exactly the same; only whitespace changes.

Common JSON syntax errors

  • Trailing commas after the last item in an object or array
  • Single quotes instead of double quotes around strings and keys
  • Unquoted keys, such as {name: "x"} instead of {"name": "x"}
  • Comments, which standard JSON does not allow
  • Special values like undefined, NaN or Infinity, which are not valid JSON

Privacy

Your JSON is parsed in your browser and is never uploaded, so it is safe to format API responses and configuration files that contain private data.

JSON Formatter questions

What does a JSON formatter do?

It adds line breaks and consistent indentation so nested objects and arrays are easy to read, without changing the data. Pretty-printed JSON is easier to review, debug and compare in version control than a single long line. It is also a quick way to spot structural mistakes, such as a value nested at the wrong level.

When should I minify JSON?

Minify JSON when size matters more than readability: API responses, files shipped to browsers and data stored in databases or caches. Removing whitespace typically saves 10 to 30% before compression. Keep a formatted copy for editing. Most servers then compress the response with gzip or Brotli for further savings.

How does JSON validation work?

The tool parses your input with the standard JSON parser. If parsing succeeds, the JSON is valid and the status says so; if it fails, the parser's message describes the problem, usually with the position of the first unexpected character.

Why is my JSON invalid?

The most common causes are a trailing comma, single quotes instead of double quotes, unquoted keys and comments. JSON is stricter than JavaScript object syntax, so code copied from a script often needs those fixes before it parses. The error message usually points to the first character the parser could not accept.

Does formatting change my data?

No. Formatting and minifying only change whitespace between tokens. Keys, values and their order stay the same. Very large numbers beyond JavaScript's safe integer range (2^53) may lose precision when parsed, so keep such values as strings. Duplicate keys are an exception: only the last value of a repeated key survives parsing.

Can I format large JSON files?

Yes, files of a few megabytes format quickly in a modern browser. Very large files, tens of megabytes or more, can make the page slow; for those, a command-line tool such as jq is a better fit. Because nothing is uploaded, there is no file size limit beyond your device memory.