Is this JSON formatter free to use?

Yes. It runs entirely in your browser — no signup, no rate limit, no data sent to a server.

Why does it say my JSON is invalid?

The three most common causes: a trailing comma after the last item, single-quoted strings or unquoted keys, or a NaN/undefined value. All four are valid JavaScript but not valid JSON.

Does formatting change my actual data?

No — it only re-indents. One exception: if your JSON has duplicate keys, the formatted output keeps only the last one, because parsing happens before formatting and duplicate keys are resolved at parse time, not a side effect of formatting.

Is my JSON uploaded anywhere?

No. Parsing and formatting happen locally in your browser tab — nothing is sent to a server.

JSON Formatter & Validator Online

Paste JSON, get it pretty-printed with 2-space indentation instantly. There's no upload step and no server round-trip — parsing and formatting both happen in your browser.

Most "invalid JSON" errors trace back to one of three things: a trailing comma after the last item in an object or array, single-quoted strings or unquoted keys (both valid JavaScript object-literal shorthand, neither valid JSON), or a stray NaN/undefined value. None of those are formatter bugs — they're the JSON spec being stricter than JavaScript.

Frequently asked questions

Is this JSON formatter free to use?: Yes. It runs entirely in your browser — no signup, no rate limit, no data sent to a server.
Why does it say my JSON is invalid?: The three most common causes: a trailing comma after the last item, single-quoted strings or unquoted keys, or a NaN/undefined value. All four are valid JavaScript but not valid JSON.
Does formatting change my actual data?: No — it only re-indents. One exception: if your JSON has duplicate keys, the formatted output keeps only the last one, because parsing happens before formatting and duplicate keys are resolved at parse time, not a side effect of formatting.
Is my JSON uploaded anywhere?: No. Parsing and formatting happen locally in your browser tab — nothing is sent to a server.

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JSON Formatter

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