JSON Formatter

What formatting does

JSON is the format most web APIs and configuration files use, and it is often delivered as one long line with no spaces. The JSON Formatter turns that line into an indented, readable structure, or does the opposite and removes all spaces to make it as small as possible. Take the compact text {"name":"Ada","tags":["a","b"],"address":{"zip":"E1 6AN","city":"London"},"active":true}. Beautified with two spaces it becomes a nested layout that is 133 characters long, and minified it is 88 characters. The data is identical in both.

The options

Three settings control the output.

• Mode: Beautify adds indentation and line breaks; Minify removes them.
• Indent: two spaces, four spaces or tabs. Two spaces is the most common convention in web projects.
• Sort keys A-Z: puts the keys of every object in alphabetical order, which makes two similar documents easy to compare. The sample above becomes {"active":true,"address":{"city":"London","zip":"E1 6AN"},"name":"Ada","tags":["a","b"]}. Arrays keep their order, because order in an array carries meaning.

Error messages that point to the problem

Real-world JSON often has small mistakes. The formatter reports each with its line and column and a hint, so you can fix it quickly.

• {"a":1,} gives "Trailing comma is not allowed in JSON" at line 1, column 8, and suggests removing the comma before the closing bracket.
• {'a':1} gives "Property names must use double quotes, not single quotes" at line 1, column 2.
• {"a":1 gives "Unexpected end of input: the object is missing its closing }".
• {"a":01} gives "Numbers cannot have leading zeros".

The rules of JSON

JSON is stricter than JavaScript object syntax, which is why code that looks right is rejected. Names and strings must use double quotes. Trailing commas are not allowed. Comments are not part of the format. Values can be strings, numbers, true, false, null, arrays and objects, and the only way to show a missing value is null. If you need to check a document against these rules without changing it, the JSON Validator does that, and for a schema use the JSON Schema Validator.

Large numbers and other limits

The tool runs JavaScript in your browser, and JavaScript stores numbers as 64-bit floating point values, so integers with more than 15 or 16 significant digits lose precision. The number 12345678901234567890 comes back as 12345678901234567000. If you handle identifiers that long, keep them as strings in your JSON. The formatter checks syntax but does not check meaning.

What to do next

To shrink JSON for production, the JSON Minifier parses first and reports errors. To compare two documents by key, use the JSON Diff Checker. To turn a list of records into a spreadsheet, use JSON to CSV. Everything runs in your browser, so API responses with private data are not uploaded.

Formatting in a workflow

A sensible routine is to format a response when you debug, minify the data you ship, and sort keys when you want a stable file that produces clean differences in version control. Keep a formatted copy of any configuration file you edit by hand, because the readable layout makes mistakes obvious before they reach production.