JSON formatter and validator
Paste JSON and have it automatically formatted, indented and validated. The tool cleanly aligns the structure, can minify it back into a single line, and on an error points out exactly where the problem is. It is handy for reading API responses, debugging configuration files, and checking whether JSON is syntactically valid. Everything runs locally in your browser — no data is sent anywhere.
How the JSON formatter works
JSON (JavaScript Object Notation) is a text format for exchanging data. It consists of objects { } with key–value pairs, arrays [ ], quoted strings, numbers, and the values true, false and null. The formatter takes your input, reads it with the browser's parser (the JSON.parse function) into a data structure, and then prints it back out (the JSON.stringify function) with your chosen indentation.
Two things happen at once. First, validation: if the input is not valid JSON, the parser fails with an error and the tool shows it, so you immediately know the data is malformed. Second, pretty-printing: valid JSON is printed with an indent of 2 spaces, 4 spaces, or a tab according to your choice, so the structure is readable at a glance. In the other direction, minification removes all redundant spaces and line breaks and produces compact single-line JSON that takes up less room in transit.
The tool works purely with syntax and structure. It does not change values, only rearranges them; the order of keys in objects is preserved exactly as the parser reads them.
How to use the JSON formatter
- Paste or type JSON into the top box (e.g. an API response or the contents of a file).
- Choose the indentation: 2 spaces, 4 spaces, or a tab.
- Click Format — the bottom box shows the neatly indented result and a ✓ Valid JSON message appears below it.
- If you need the compact form instead, click Minify.
- If the input is malformed, instead of a result you'll see an error message describing the problem (e.g. the position where the parser hit an unexpected character).
Example of turning messy input into formatted output:
| Input | Output (2 spaces) |
|---|---|
{"name":"John","age":30,"tags":["a","b"]} | { |
What the JSON formatter is good for
It is most appreciated by developers and API testers: a server response is often packed onto a single line and hard to read — the formatter expands it into a clear shape. It is also useful for checking configuration files (package.json, tool settings, manifests), where a single missing comma or quote breaks the whole file; validation tells you exactly where to look for the mistake.
Minification is handy when you want to embed JSON in code, a URL, or transfer it as small as possible — the compact form saves bytes. The tool also helps with comparing and debugging data, when you need consistent indentation so differences are easy to spot.
Because processing happens entirely in your browser, it is safe to paste even more sensitive data — configs, tokens, or internal responses. Nothing is sent to a server, so the content never leaves your device. General caution still applies: don't accidentally copy a password or secret key somewhere else.
FAQ
What does it mean that JSON is "valid"?
That it exactly matches JSON syntax: properly closed brackets, keys and string values in double quotes, commas between elements, and no extra comma at the end. If any of that is missing, the parser reports an error.
Why does it report an error even though the JSON looks correct?
The most common causes are single quotes instead of double quotes, a comma after the last element (a trailing comma), comments (JSON does not allow them), or an unclosed bracket. The error message usually gives the position where the parser hit the problem.
What is the difference between formatting and minifying?
Formatting (pretty-print) adds indentation and line breaks so the JSON is readable for a human. Minifying does the opposite — it removes all redundant spaces and produces a compact single-line form suitable for transfer and machine processing.
Is my data sent anywhere to a server?
No. Both formatting and validation happen entirely in your browser using the built-in JSON parser. The pasted text goes nowhere, so it is safe to work with internal or sensitive data.
Does the tool preserve the order of keys?
Yes, keys are printed in the order the parser reads them from the input. The tool does not reorder or alphabetically sort keys.
Does it support tab indentation?
Yes. In the dropdown you can choose 2 spaces, 4 spaces, or a tab. A tab is suitable if your project uses tab indentation across files.
Can it handle very large JSON?
Processing is limited only by the performance of your device and browser. It handles ordinary API responses and configs instantly; for files of many megabytes, formatting may take a moment.
Will the tool fix broken JSON for me?
No. The tool only finds and reports the error; it does not guess what you meant and does not edit the data itself. You have to make the fix (e.g. adding quotes or removing an extra comma) manually in the input.
Sources & standards
📅 Last updated: 11 July 2026