JSON Formatter and Validator

What the formatter changes

Formatting only changes the whitespace between values: line breaks and indentation for Format, and none at all for Minify. Everything else is copied exactly as you wrote it:

• Numbers keep their original digits. 1.50 stays 1.50, 1e3 stays 1e3, and a 19-digit ID is not rounded.
• Strings keep their escape sequences, so \u00e9 is not turned into é and nothing is re-encoded.
• Key order stays the same unless you switch on Sort keys A to Z. Sorting is recursive, so keys inside nested objects are sorted too, but the order of items in an array never changes. Keys are compared by character code, as jq does, so capital letters come before lower-case ones.

How validation works

The tool checks your JSON against the standard (RFC 8259) as you type and reports the first problem with its line and column. When you press Format, it selects the faulty character in the input and shows an excerpt with a marker under it. The checking is done by the tool itself rather than by the browser, so the message and the position are the same in Chrome, Firefox and Safari.

These are the mistakes it explains most often:

• a trailing comma before } or ], or a missing comma between two values
• single quotes or curly quotes instead of straight double quotes
• property names without quotes, as written in JavaScript code
• comments, NaN, undefined, and Python's True, False and None
• numbers with leading zeros, such as 0123
• brackets or strings that are never closed, and line breaks inside strings
• invisible characters, such as non-breaking spaces copied from a web page

It also warns about two things that are valid but risky: the same key repeated inside one object (most programs keep only the last value) and whole numbers larger than 9,007,199,254,740,991.

Large numbers and precision

JavaScript stores numbers as 64-bit floating point values, which hold whole numbers exactly only up to 2^53 − 1 (9,007,199,254,740,991). Formatters that parse the JSON and write it out again silently change a value such as 12345678901234567890 into 12345678901234567000. This formatter copies the digits instead. The program that later reads your JSON may still round them, so store such IDs as strings when the exact value matters.

Privacy

Your JSON is processed by JavaScript on your own device. It is not uploaded, logged or stored, so you can use the tool for API responses and configuration files that contain private data. Large inputs are handled in a background thread of your browser to keep the page responsive.