Utilore

JSON Validator

Paste the file and get a straight answer: valid or not. If not, the message says what the parser expected and at which position — usually a trailing comma or a missing quote.

How to use

  1. Paste the JSON into the box — the check runs on every keystroke.
  2. Read the line under the box: green means valid, red carries the parser's own message.
  3. Fix the reported spot and watch the message turn green.

Good to know

The four mistakes behind most errors

A trailing comma after the last element, single quotes instead of double, an unquoted key, and a stray comment. JSON allows none of them, although JavaScript, Python and YAML each allow some — which is exactly why they slip in.

Valid is not the same as correct

This page checks syntax, not meaning. A file can parse perfectly and still miss a required field or hold a string where a number belongs. For that you need a schema, not a parser.

Frequently asked questions

Is my file uploaded for checking?

No. Validation uses the parser built into your browser, so the data never leaves the device.

Which standard is used?

The same one every runtime follows — RFC 8259, via JSON.parse. What passes here passes everywhere.

Why is a trailing comma an error?

JSON has no optional trailing comma: after the last element the parser expects a closing bracket. JavaScript tolerates it, JSON does not.

Can I check very large files?

Up to five megabytes of text. Larger files are better checked with a command-line tool.

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