Paste JSON to format it with 2 spaces, 4 spaces or tabs, or minify it to one line. The formatter validates as you type and points to the exact line and column of any error, such as a trailing comma or single quotes.
The preview is shortened. Copy and Download include the whole result.
Your text never leaves your device.
Formatting never changes the data. Keys keep their order, strings keep their escape sequences exactly as written (an escaped é stays escaped), and numbers keep their exact digits.
| Error message | Typical cause | Fix |
|---|---|---|
| trailing comma | [1, 2, 3,] |
delete the last comma |
| single quotes | {'a': 1} |
use double quotes for keys and strings |
| unexpected character | unquoted key {a: 1}, undefined, NaN, +1, .5 |
quote the key; use null for missing values; write 1 and 0.5 |
| extra data after the end | a comment, or two objects one after another | remove comments; wrap several objects in an array |
| invalid number | a leading zero: 01.50, 007 |
write 1.50 and 7, or make the value a string |
| a string is not closed | a missing closing quote, or a raw line break inside a string | add the quote; write line breaks as \n |
| tabs and other control characters | a tab pasted inside a string | replace it with \t |
Columns count characters as you see them, so an emoji earlier on the line counts as one column.
{ name: 'Ada' } is valid JavaScript but not JSON. Quote the keys and switch to double quotes.Paste it into the box above. If it is valid, it is formatted immediately with 2-space indentation; choose 4 spaces or tabs if your project uses them. If it is not valid, the status line shows the line and column of the first error and what is wrong there.
The most common causes are a trailing comma after the last item, single quotes instead of double quotes, keys without quotes, comments (// or /* */), and values like undefined, NaN or .5. All of these are allowed in JavaScript but not in JSON. The error message names the problem and its position.
No. Many online formatters run JSON.parse, which turns 12345678901234567890 into 12345678901234567000 and 1.0 into 1, because JavaScript numbers have only about 16 significant digits. This formatter re-indents the original text instead, so every number, string escape and key stays exactly as you wrote it, including duplicate keys.
Yes. Formatting and validation happen in your browser and nothing is uploaded or logged. That is worth checking with any online tool, since API responses and config files often contain tokens and personal data.
Yes. Inputs larger than about 500 KB are formatted in a background thread, so the page stays responsive; a 5 MB file formats in well under a second on a typical laptop. The preview shows the beginning of very large results, while Copy and Download always give the complete output.