Online JSON Formatter: What Formatting Changes in Your JSON

Pretty-Print, Minify or Validate

• Format JSON pretty-prints with a two-space indent and shows the number of keys and the output size.
• Minify JSON removes all whitespace outside strings, which makes files smaller for sending or storing.
• Validate JSON only checks that the text parses.

Input:  {"name":"devmeldex","tools":["json","regex"],"free":true}

Format JSON:
{
  "name": "devmeldex",
  "tools": [
    "json",
    "regex"
  ],
  "free": true
}

If the input is not valid, the tool shows your browser's parser error instead of an output. In Chrome and Edge, a trailing comma such as {"a":1,} gives Expected double-quoted property name in JSON at position 7 (line 1 column 8). Other browsers word it differently. The formatter page lists the most common syntax errors and how to fix them.

What Formatting Can Change in Your Data

Formatting parses your JSON into JavaScript values and writes them back out. That round trip keeps strings, booleans and normal numbers exactly, but it changes four things:

Input:  {"b":1,"2":2,"a":3,"1":4}
Output: {"1":4,"2":2,"b":1,"a":3}

Input:  {"id":12345678901234567890}
Output: {"id":12345678901234567000}

Input:  {"a":1,"a":2}
Output: {"a":2}

Input:  {"s":"caf\u00e9"}
Output: {"s":"café"}

These are JavaScript rules, not JSON rules. Python's json module, for example, keeps large integers exactly and keeps keys in their original order, although it also keeps only the last value of a duplicate key.

Validation Checks Syntax, Not Your Data

Valid JSON can still be wrong for your application: a missing required field, a number where a string is expected, or an unexpected extra key all pass validation. To check structure and types, validate against a JSON Schema in your code or build pipeline. To compare two versions of a response or config file, format both the same way and compare them with the Diff Checker, so only real changes are highlighted.

Working With Large Files

Everything runs in your browser, so the limit is your device rather than an upload size. In our test on a desktop computer, formatting 10 MB of JSON took under a second; pasting that much text into the input box took a few seconds. Results longer than 200,000 characters are shown as a preview so the page stays responsive, and Copy Output always copies the full result.

Converting JSON to CSV

JSON to CSV works best with an array of flat objects: each object becomes a row and each key a column. Nested objects and arrays are written into one cell as JSON text, so flatten them first if you need separate columns.

If a cell starts with =, +, - or @, the tool warns you, because spreadsheet apps such as Excel may treat it as a formula when you open the file. The CSV text itself is not changed, so check those cells before opening it.

Conclusion

Formatting makes JSON readable and catches syntax errors, but it is a round trip through JavaScript. Send long IDs as strings, avoid duplicate keys, and validate structure separately when it matters.