Is the JSON validator free?
Yes. This JSON validator is completely free to use with no signup or account required.
Does this upload my JSON?
No. Validation happens entirely in your browser on your own device, so your JSON is never uploaded to a server and stays private.
Does it show the parsed output too?
Yes. Valid JSON is displayed in a readable, formatted form so you can confirm it and inspect the structure.
What happens if my JSON is invalid?
The validator reports a clear parse error so you can find the misplaced comma, bracket, or quote instead of getting broken output.
Does it work on mobile?
Yes. The validator runs in any modern browser, including mobile, since all processing happens locally on your device.
Why is my JSON invalid when it looks fine?
The four usual causes are a trailing comma after the last item, a comment, a single-quoted string and an unquoted key. All four are valid JavaScript, which is why they look right, and none of them is valid JSON. The error position in the message points at where the parser gave up, which is usually one character after the real problem.
Does it check my JSON against a schema?
No. This checks that the document parses, which is a syntax question. Whether the document has the right fields, the right types or the right values is a schema question and needs a schema validator. Valid JSON can still be entirely wrong data.
What happens if I have the same key twice?
The document validates and the last value wins. The JSON specification permits duplicate keys and leaves the behaviour to the parser, and every browser keeps the final one. This is a real source of silent data loss, so if a field is mysteriously not what you set, search the document for a second copy of the key.
Can it validate a JSON Lines or NDJSON file?
No. Those formats put one JSON document per line and the whole file is not itself valid JSON, so the parser rejects it at the start of the second line. Validate a single line at a time, or wrap the lines in an array with commas between them.
Why does it show my JSON formatted after validating?
Because the parse produces a real structure, and printing it back with indentation is free. It also serves as a second check: if the reformatted output looks wrong, for example a field missing that you expected to see, the input said something different from what you thought it said.
Is my JSON uploaded?
No. Validation uses the browser's own JSON.parse in the page. Nothing is sent to a server, which matters given how often the JSON people need to validate is a real API response with real credentials in it.