Complete JSON Guide & Reference

What is JSON?

JSON (JavaScript Object Notation) is a standardized, language-independent data interchange format defined by RFC 8259 and ECMA-404. It uses human-readable text to store and transmit data objects consisting of attribute-value pairs and arrays.

The 6 Supported JSON Data Types

Strict JSON supports exactly six data types. Any other type (such as functions, undefined, or Symbols) is invalid in JSON.

{
  "string": "UTF-8 text wrapped in double quotes",
  "number": 42.5,
  "boolean": true,
  "null": null,
  "array": [1, 2, 3],
  "object": {
    "key": "value"
  }
}

1. Strings

Strings must always be enclosed in standard double quotes ("). Single quotes (') and backticks (`) are illegal in standard JSON.

Special characters must be escaped using a backslash (\):

• \" — Quotation mark
• \\ — Reverse solidus (backslash)
• \/ — Solidus (forward slash)
• \b — Backspace
• \f — Form feed
• \n — Newline
• \r — Carriage return
• \t — Horizontal tab
• \uXXXX — 4-hex-digit Unicode character

{
  "quote": "She said, \"Hello!\"",
  "backslash": "C:\\Users\\AppData",
  "newline": "First line\nSecond line",
  "unicode": "\u2602 (umbrella emoji)"
}

2. Numbers

JSON numbers can be integers, decimal fractions (floats), or exponential/scientific notation (e.g. 1.5e3). Leading zeros (like 05), hexadecimal (0xFF), NaN, and Infinity are not permitted.

3. Booleans

Booleans are written in lowercase: true or false. Title-cased values like True (common in Python) will cause parse errors.

4. Null

The keyword null represents an intentional absence of value.

5. Objects

An unordered set of name/value pairs wrapped in { }. Every key must be a valid string enclosed in double quotes followed by a colon :.

6. Arrays

An ordered collection of values wrapped in [ ], separated by commas. Arrays can contain mixed data types or nested arrays/objects.

Fundamental JSON Syntax Rules

• Double Quotes Only: All object keys and string values must use double quotes.
• No Trailing Commas: Commas can only appear between items, never after the last item.
• No Comments: The official JSON specification does not support single-line (//) or multi-line (/* */) comments.
• UTF-8 Encoding: JSON text is serialized in UTF-8 by default.

JSON vs. JavaScript Objects

While JSON syntax is derived from JavaScript object literal syntax, they have important differences:

• In JavaScript, object keys do not require quotes; in JSON, keys must be double-quoted.
• JavaScript supports single quotes, template strings, functions, undefined, and trailing commas; JSON prohibits all of them.
• JSON is purely a data format, not a programming language.

Helpful Tools

Validate your JSON syntax against these rules in our JSON Validator, pretty-print it in the JSON Formatter, or read the Common JSON Errors Guide.