RunToolRunJSON Formatter
Format and beautify JSON data.
How to Format and Validate JSON
Paste your JSON
Drop raw, minified or messy JSON into the input field.
Format or minify
Pretty-print with proper indentation for reading, or minify to a single line for production.
Copy the result
Grab the clean output — validation errors are reported with details if the JSON is broken.
JSON is stricter than it looks
The format allows no comments, no trailing commas, and no single quotes around strings or keys. Every key must be a double-quoted string. These rules catch people constantly, because JavaScript object literals allow all of those things and JSON looks like a JavaScript object literal.
That strictness is deliberate. JSON was designed to be unambiguous across every language that parses it, and each convenience it refuses is a place where two parsers might disagree. A formatter that accepts your file is telling you something useful: that any other parser will accept it too.
What the error message is really saying
Parse errors report the position where parsing became impossible, not where the mistake is. A missing closing brace is reported at the end of the file; a trailing comma is reported at the token after it. The fault is almost always earlier than the reported position.
The fastest way to locate it is to format the file: valid sections indent cleanly and the structure becomes visible, so a block that does not line up with its neighbours stands out immediately. Reading raw minified JSON to find a syntax error is doing the hard version of an easy job.
Numbers lose precision, silently
JSON numbers have no size limit in the specification, but most parsers read them into a double-precision float, which represents integers exactly only up to about 9 quadrillion. A 19-digit identifier — common in databases and social platforms — will be silently rounded, and the value you get back is not the value that was sent.
This is one of the few JSON problems that produces no error at all. The defence is to transmit large identifiers as strings. If an API returns them as numbers and the last digits look wrong, this is why.
Duplicate keys and key order
The specification does not forbid duplicate keys, and it does not say what a parser should do with them. Most take the last one. Some take the first. A file with duplicates is valid JSON that means different things to different readers, which is a genuinely dangerous property.
Key order is similarly unspecified. Objects are unordered by definition, so a formatter may preserve the original order or sort alphabetically, and neither is wrong. If your code depends on key order, it depends on something the format does not promise.
Formatting, minifying, and where it runs
Indented JSON is for humans reading it; minified JSON is for transmission, where the removed whitespace is real bandwidth. Neither changes the data, so switching between them is always safe.
Parsing and formatting happen in your browser. API responses, configuration files and exported records routinely contain credentials, tokens and personal data, and pasting those into a server-side formatter hands them to someone else. Here nothing is transmitted.