JSON formatter and validator

What this tool does

It parses your input with the browser's own JSON engine. If parsing succeeds, the data is re-printed with consistent indentation and you get a node count and character length. If it fails, you get the parser's exact error message, which usually names the position of the problem.

The errors you will hit most

• Trailing commas. {"a": 1,} is valid JavaScript and invalid JSON.
• Single quotes. JSON requires double quotes around both keys and string values.
• Unquoted keys. {a: 1} is an object literal, not JSON.
• Comments. JSON has none. Formats like JSONC and JSON5 add them, but standard parsers reject them.
• NaN, Infinity or undefined. None are valid JSON values; use null.

Formatting conventions

Two spaces is the common default and what most linters expect. Tabs are preferred by teams that want each developer to control the visible width. Minified output removes all optional whitespace, which matters when JSON is embedded in a page or sent over a slow connection — though if you are serving JSON over HTTP, gzip or Brotli compression saves considerably more than minification does.

A note on large files

Everything happens in the browser tab, so very large documents are limited by available memory rather than any upload cap. Several megabytes is normally fine; tens of megabytes may be slow. For genuinely large data, a command-line tool such as jq is a better fit.

Questions

Is my data sent anywhere?

No. The parsing happens in your browser with the built-in JSON engine. You can disconnect from the internet and the tool still works.

Why does my API response fail to parse?

Most often the response is not JSON at all — an HTML error page or a redirect. Check the content type and the status code before parsing.

Does it sort or filter keys?

No. It preserves the structure exactly and only changes whitespace, so the output is always equivalent to the input.

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