JSON formatter & validator
Paste JSON to format and check it. Everything happens in your browser — nothing is uploaded, saved or shared, so there's nothing to leak.
Formatted JSON will appear here
Questions
Is my JSON uploaded anywhere?
No. Formatting and validation run entirely in your browser, and there's no save or share feature. Your data never reaches our server, so it can't leak, be logged or be scraped. It isn't even kept in your browser's storage: close the tab and it's gone.
Why does that matter?
In November 2025, security researchers found that popular online formatters had exposed more than 80,000 saved snippets, including passwords, API keys and cloud credentials, and that attackers were already harvesting them (BleepingComputer). People paste config files and API responses into these tools all the time. They shouldn't end up public.
What does “Fix it” do?
It repairs common near-JSON: trailing commas, single quotes, unquoted property names, missing commas between properties, // and /* */ comments, and Python's True, False and None. You can paste a JavaScript object or a Python dict and get valid JSON back. Anything it can't repair safely is left for you to fix, with the exact line and column.
Why are my large numbers different in other formatters?
Most formatters use JavaScript's JSON.parse, which silently rounds integers larger than 9,007,199,254,740,991. An ID like 12345678901234567890 becomes 12345678901234567000. justformat.dev keeps every number exactly as you wrote it.
How do I minify JSON?
Set Indent to Minify. The output removes all whitespace, ready to copy.
Does it handle large files?
Yes. Typical API responses format instantly, and files of several megabytes take around a second. Very large results are previewed without colour, and only the first megabyte is shown, to keep the page responsive. Copy and Download always give the full result.