JSON Formatter and Validator - Line and Column Errors

The frustrating part of a broken JSON payload is rarely knowing that it is broken; it is knowing where. A bare “unexpected token” message is little help when the payload is four hundred lines long. This tool leans on the fact that the browser’s own JSON.parsealready knows where it gave up: when parsing fails it reports either a character position into the string or, in some browsers, a line and column directly. The tool turns whichever it gets into a line and column and draws a caret under the exact character, so the search is over before it starts.

Validation also runs as you type, not only when you press a button. The status line above the editor flips between valid and invalid on every keystroke, which means you can paste a payload and immediately see whether it parses, and watch it become valid as you fix the flagged spot. Formatting and minifying stay explicit actions, because those change the text and you should decide when that happens, but the yes-or-no of validity is answered continuously.

Because the check uses the same parser your JavaScript runtime uses, the verdict is exactly the one your code will reach. There is no second, slightly different validator with its own quirks; if this tool says the payload is valid, JSON.parse in your application will agree, and if it rejects it, so will your code.

It is reasonable to worry that reformatting might alter data, so it is worth being precise about what happens. The tool parses your text into values and then re-serializes them, which means the output is canonical JSON rather than a character-for-character copy. The keys, the values, the arrays, and the nesting are identical. Key order is preserved, because the parser keeps the order it encountered and JSON.stringify writes them back in that order.

The one visible normalization is in numbers. Because a parsed number is just a number, a value written as 1.0 comes back as 1, and 1e3 comes back as 1000; these are the same value in a canonical form. If you are working with numbers so large that they lose precision as JavaScript doubles, that is a limitation of JSON numbers in JavaScript generally, not of this tool, and such values are usually best carried as strings.

Everything runs in your browser’s memory. The parse, the live validation, the formatting, and the minify never touch a network, so a payload full of tokens, credentials, or personal data stays on your machine. That is why the tool is safe for exactly the sensitive payloads people most often need to inspect.

JSON is often one step in a chain. If you are moving between formats, the YAML Converter turns JSON into the more human-friendly YAML and back, and the CSV to JSON Converter bridges tabular data and JSON arrays. When a payload arrives base64-encoded, the Base64 Converter decodes it back to text you can paste here to format and validate.