JSON Formatter and Validator

How JSON Formatting Works

JSON (JavaScript Object Notation) is a lightweight text format for exchanging structured data. It is defined by ECMA-404 and RFC 8259. The format consists of two structures: objects (collections of key-value pairs enclosed in curly braces) and arrays (ordered lists enclosed in square brackets). Keys must be strings enclosed in double quotes, and values can be strings, numbers, booleans (true / false), null, nested objects, or arrays.

Formatting (also called pretty-printing or beautifying) adds newlines and indentation to make JSON easier to read. Minifying removes all whitespace to produce the smallest possible string, which is useful for reducing file sizes in APIs and config files. This tool uses the browser's native JSON.parse() to validate and then JSON.stringify() with an indent argument to produce formatted output.

Worked Example

Given the following minified JSON input (the default in this tool):

With 2-space indentation selected, the formatter produces:

The input has 4 top-level keys, an input size of 60 characters, and a formatted size of 95 characters.

Common JSON Errors

• Trailing comma: {"a":1,} is invalid. Remove the comma after the last key-value pair or array element.
• Single quotes: {'name':'Alice'} is invalid. All keys and string values must use double quotes.
• Unquoted keys: {name:"Alice"} is invalid. Keys must always be quoted strings.
• Undefined or NaN: JavaScript's undefined, NaN, and Infinity are not valid JSON values. Use null instead, or convert numbers to strings.
• Comments: JSON does not support comments. Remove any // or /* */ before parsing.
• Unescaped control characters: Literal tab or newline characters inside a string value must be escaped as \t or \n.

When to Use JSON vs Other Formats

JSON is the default data exchange format for REST APIs, web browser storage (localStorage, sessionStorage), and configuration files for Node.js projects and many modern tools. For configuration files that benefit from comments, YAML or TOML are popular alternatives. For binary efficiency over the wire, formats such as MessagePack or Protocol Buffers are used. For human-authored config where schema validation matters, JSON Schema can be layered on top of JSON.

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Method: Validation and formatting use the browser's built-in JSON.parse() (ECMA-404 / RFC 8259) and JSON.stringify(indent). No server-side processing. Input size is measured in UTF-16 code units (same as JavaScript's String.length).

This tool processes all data locally in your browser. No input is transmitted or stored anywhere. Suitable for sensitive JSON content such as API keys, tokens, and configuration data.