JSON validator

Check your JSON exactly.

Paste or open JSON to see whether it parses, where the first error is, and how it looks formatted — with big integers preserved digit for digit.

Drop a JSON file

Up to 5.00 MB — or paste below.

Choose a file

How it works

  1. 01Paste JSON or open a .json file (up to 5 MB).
  2. 02Validate to get the parse error with its line and column.
  3. 03Format or minify without rewriting numeric literals.
  4. 04Copy or download the result.

Precision

A normal parse turns 9007199254740993 into 9007199254740992. FormatOnce keeps the original digits, so IDs and high-precision decimals round-trip unchanged.

Questions & limits

Is an empty box valid JSON?
No. Empty input is reported as invalid rather than passing quietly.
Why does my huge ID change in other tools?
JavaScript numbers lose precision above 9007199254740991. FormatOnce parses and prints numbers losslessly, so nothing is rewritten.
Does it support JSON5 or comments?
No. Validation follows standard JSON, so trailing commas and comments are reported as errors.
Where does the data go?
Nowhere. Validation runs in this tab, and clearing the field or closing it removes the content from memory.