What is JSON formatting?
JSON (JavaScript Object Notation) is a lightweight data interchange format. This free online JSON formatter takes minified or messy JSON and outputs clean, indented, syntax-highlighted JSON that's easy to read and debug. All processing happens in your browser — your data never leaves your machine.
Why validate JSON before you ship it
A single misplaced comma or an unquoted key can break an entire API response, configuration file, or data import. JSON validation catches these problems instantly by parsing your input against the official JSON grammar and pointing to the exact character where parsing failed — so you fix the cause, not the symptom.
Formatting and validation happen together. To format JSON the tool must first parse it, which means invalid JSON is caught in the same step: valid JSON is re-indented and highlighted, while invalid JSON surfaces a clear error message with the position of the problem.
Formatting vs. minifying
Formatting — also called beautifying or pretty-printing — adds indentation and line breaks so JSON is easy for a human to read and debug. Minifying does the opposite: it strips every non-essential space and newline to produce the smallest possible payload, which is what you want for production API responses and network requests. Both produce identical data; only the whitespace differs.
Common causes of invalid JSON
Most JSON errors come from a small set of mistakes: a trailing comma after the last item, single quotes instead of double quotes, keys left unquoted, a missing comma between items, or an unescaped quote or control character inside a string. Values like NaN, Infinity, and undefined are also invalid in standard JSON.
When a parser reports an error, start at the position it names and scan backwards — the real cause is often a few characters earlier, such as a missing closing brace or bracket that only surfaces later in the text.
How to format and validate JSON online
- 1Paste your JSON. Paste or type your JSON into the input panel — an API response, a config file, or a single object.
- 2Choose an action. Select Format to beautify and indent, Minify to compress, or Validate to check the structure without changing the layout.
- 3Read any errors. If the JSON is invalid, the tool describes what went wrong and where — for example an unexpected token or a trailing comma.
- 4Explore with Tree view. Switch to Tree view to expand and collapse nested objects and arrays and inspect the structure visually.
- 5Copy the result. Use Copy output to copy the formatted or minified JSON to your clipboard.
Examples
Beautify messy JSON
Input
{"id":42,"tags":["a","b"],"ok":true}Output
{
"id": 42,
"tags": ["a", "b"],
"ok": true
}Minify formatted JSON
Input
{
"id": 42,
"ok": true
}Output
{"id":42,"ok":true}Trailing comma (invalid)
JSON does not allow a comma after the last element.
Input
{"a":1,"b":2,}Output
Error: Unexpected token } — remove the trailing comma
Single quotes (invalid)
Keys and strings must use double quotes.
Input
{'name':'Ada'}Output
Error: Unexpected token ' — use double quotes
JSON data types
Every JSON value is one of six types.
| Type | Example |
|---|---|
| String | "hello" |
| Number | 42, -3.14, 2.5e8 |
| Boolean | true, false |
| Null | null |
| Object | { "key": "value" } |
| Array | [1, 2, 3] |
Frequently asked questions
Is my JSON data sent to a server?+
No. All formatting, validation, and minifying happen locally in your browser using JavaScript. Your data never leaves your machine, which makes the tool safe for sensitive or proprietary payloads.
What does "Unexpected token" mean?+
The parser reached a character it did not expect for valid JSON — commonly a trailing comma, single quotes instead of double quotes, an unquoted key, or a missing comma between items. The error points to where parsing stopped.
What is the difference between formatting and validating?+
Validating checks whether your JSON conforms to the JSON grammar and reports errors. Formatting parses the JSON and re-prints it with clean indentation. Formatting includes validation, because JSON must be parsed before it can be re-printed.
Can it handle large JSON files?+
Yes. Because processing runs in your browser, the practical limit is your device's memory rather than an upload cap. Multi-megabyte files format in place with no round trip to a server.
Does it support comments or JSON5?+
Standard JSON does not allow comments or trailing commas, so those are reported as errors. The tool validates against the official JSON specification (RFC 8259).
What indentation does it use?+
You can choose 2-space or 4-space indentation. Two spaces is the most common convention and matches the defaults of most linters and editors.
Is it free?+
Yes — completely free, with no sign-up, no account, and no usage limits.
Can I convert the formatted JSON to other formats?+
Yes. Once your JSON is valid you can convert it with the related JSON to CSV and JSON to YAML tools, or compare two documents with JSON Diff.