What makes JSON invalid?

Trailing commas, comments, single quotes, unquoted keys and unescaped line breaks inside strings.

Does it check against a schema?

No. It checks syntax. Schema validation needs a schema tool.

Not in standard JSON. Formats such as JSON5 allow them, but most parsers do not.

Yes. Nothing is uploaded or logged.

Check whether a JSON document parses before you ship it. Valid input is summarised; invalid input gets the parser's error message.

Paste JSON to check

The result appears as soon as you paste something.

Validation runs as you paste, with no button to press.

Valid documents report their top-level type and size.

The parser message points at what went wrong.

Nothing is uploaded to a server, so your content stays on your device.

No account, no watermark and no daily limit.

Large tap targets and layouts that fit a phone screen.

Beautify or minify JSON and catch syntax errors.

Decode a Base64 string back into readable text.

Turn a percent-encoded URL back into readable text.

Deduplicate any list, with sorting and case options.