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JSON Formatter

Format, validate and minify JSON

Pretty-print or compact JSON, sort keys, and find the exact line and column of syntax errors.

How to use JSON Formatter

  1. Paste JSON into Input JSON, drop a file on it, or use Open file or Try an example.
  2. Pick an Action: Format to pretty-print, Minify to remove all whitespace, or Validate to only check the syntax.
  3. For Format, choose an Indent of 2 spaces, 4 spaces or a tab. Tick Sort keys (recursively) to order every object’s properties.
  4. If the JSON is invalid, read the message with its line and column, and use Jump to error in input to select the spot.
  5. Copy the result, Download .json, or use Send to… to open it in another tool.

How it works

The input is checked by a strict JSON parser (RFC 8259) written for this tool. It reads the text in one pass without recursion, so very deeply nested documents can’t overflow the stack, and it stops at the first error with a specific message, such as a trailing comma, single quotes, a comment or a missing comma, plus its line and column.

Numbers and strings keep the exact text they were written with. A long ID such as 12345678901234567890 isn’t rounded the way JSON.parse would round it, and escapes like \u00fc stay as escapes. Formatting rewrites only the whitespace between values, and sorting reorders properties by key, comparing the keys character by character (so uppercase letters come before lowercase). Everything runs on the page, on a deferred copy of the input so typing stays responsive.

Limits

  • Strict JSON only: comments, trailing commas, single quotes, unquoted keys, NaN and Infinity are reported as errors. JSON5, JSONC and JSON Lines aren’t supported.
  • Input over 20,000,000 characters (about 20 MB) isn’t processed. Opened or dropped files can be up to 10 MB.
  • Output longer than 1,000,000 characters is cut short on screen; Copy and Download .json still give all of it.
  • Duplicate keys are kept in the output and flagged (the first five are named), because most other parsers keep only the last value.
  • Numbers with more than 15 significant digits are flagged: they are kept exactly here, but JSON.parse in other programs may round them.

Privacy

Your JSON is parsed and formatted in your browser and never uploaded or stored. Copy share link puts the input and options in the link’s # fragment, which browsers don’t send to servers; links are limited in size, so large documents show Too large to share. If you use Send to…, the output is handed over through this tab’s session storage and removed as soon as the other tool reads it.

Frequently asked questions

Why does the formatter accept my big numbers when other tools round them?

JavaScript numbers hold about 15–17 significant digits. This tool never converts numbers; it keeps the digits you wrote, so 12345678901234567890 comes out unchanged. It warns you because other parsers may still round it.

Can it fix JSON with comments or trailing commas?

No. It validates strict JSON and points at the first problem, with a hint such as trailing comma? or Comments aren’t allowed in JSON. Remove those parts and the rest is formatted.

Does sorting keys change arrays?

No. Only object properties are reordered, at every level. Array items keep their order.

What happens to duplicate keys?

They are kept, in their original order, and listed in a warning. JSON allows them, but most parsers keep only the last value, so it is usually worth removing them.

Is a single value like "hello" or 42 valid JSON?

Yes. Any JSON value can be the whole document, not just an object or array, and it is formatted as is.

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