JSON Formatter — No Upload, No Logs, Instant

About JSON Formatter

JSON (JavaScript Object Notation) is a lightweight, text-based data format built from two structures: objects, which are unordered collections of key-value pairs wrapped in curly braces, and arrays, which are ordered lists wrapped in square brackets. Values can be strings, numbers, booleans, null, or further nested objects and arrays. It became the default format for web APIs and configuration files because it is human-readable, language-agnostic, and maps cleanly onto the data structures of almost every programming language. A formatter takes the compact or inconsistently-spaced JSON that machines emit and re-indents it so a person can actually read the hierarchy.

This tool parses your input with the browser's native JSON.parse and re-serializes it with JSON.stringify using either 2- or 4-space indentation. Because it does a full parse before printing, it doubles as a validator: if the text is not strictly valid JSON, parsing fails and you get an error instead of malformed output. That round-trip also normalizes the data — duplicate object keys collapse to the last value, and the output reflects exactly what a conforming parser would see, which is often more useful than a purely cosmetic reformat.

The most common reasons valid-looking JSON is rejected are details the format is strict about. Keys and string values must use double quotes, never single quotes. Trailing commas after the last element of an object or array are not allowed. Comments are not part of the JSON specification, so any // or /* */ will cause a parse error. Numbers cannot have leading zeros or a trailing decimal point, and undefined, NaN, and Infinity are not valid JSON values. JavaScript object literals tolerate many of these; JSON does not.

Use a formatter when you copy a minified API response and need to find a specific field, when you are diffing two payloads and want consistent indentation so the diff is meaningful, or when you are hand-editing a config file and want to confirm it still parses before you ship it. The main limitation to keep in mind is that JSON has no native type for dates, big integers beyond IEEE-754 double precision, or binary data — those are conventionally carried as strings. Everything here runs in your browser; the JSON you paste is never sent to a server.