Frequently Asked Questions
Short answers to the stuff people ask most. If yours isn't on the list, send it through the contact page. That's usually how new ones end up here.
A free online JSON formatter and validator that runs entirely in your browser. Paste a chunk of JSON (or a URL that returns JSON), pick which spec to check it against, and you get it back cleanly indented, with syntax highlighting and a collapsible tree you can click through. Handy for eyeballing an API response or untangling a config file.
Free, and no. No sign-up, no login, no daily limit. Open the page and start pasting.
No. Everything (the parsing, the formatting, the validation, the JWT decoding) happens locally in your browser, so your JSON never touches our servers. Your recent runs live in sessionStorage and disappear the moment you close the tab, and the only thing kept between visits (localStorage) is your two preferences: the spec and the indentation you last picked. That's it.
Five: RFC 8259, RFC 7159, RFC 4627, ECMA-404, and JSON5. You choose the one you want to validate against from the dropdown.
Honestly, for the first four, nothing you'll notice: RFC 8259, 7159, 4627, and ECMA-404 all describe the same strict JSON, so they behave identically here. JSON5 is the odd one out. It's a looser superset that lets you use comments, single quotes, unquoted keys, and trailing commas, which is what you want when a config-style file bends the rules on purpose.
Yep. Instead of pasting, drop a URL into the box and it fetches the JSON and formats it for you. Your browser makes that request directly, so it needs a connection, and the URL has to allow it (CORS still applies).
When something's off you get an INVALID banner with the spec name and, more usefully, the exact line and column of the problem plus a small compiler-style code frame with an arrow pointing at the bad line. It also catches the classic trailing comma, the one most parsers blame on the wrong line and send you hunting in the wrong place.
Two, three, or four spaces, a tab, or Compact if you want it minified down to a single line. Switch between them and the output updates.
Yep, once the page has loaded. All five specs run in your browser, JSON5 included (that parser ships with the site now, it doesn't come from anywhere else), so formatting and validating keep working with the connection off. The one thing that still needs the network is pulling JSON from a URL, since that's a real request going out.
Usually one of three things strict JSON doesn't allow: a trailing comma after the last item, single quotes instead of double, or keys without quotes. Check the line the error points to. Or, if you're using that syntax on purpose, switch the spec to JSON5 and it'll pass.
Head to the contact page and send a message with your name, email, and what's up. Every one gets read, and bug reports and ideas are genuinely how the tool gets better.