JSON Format Explained

What is JSON?

JSON (JavaScript Object Notation) is a lightweight, text-based data interchange format. It was originally derived from JavaScript object literal syntax but is now completely language-independent. JSON is defined by RFC 8259 and is the de-facto standard format for REST APIs, configuration files, and data storage.

JSON is designed to be easy for humans to read and write, and easy for machines to parse and generate. A JSON document is always valid UTF-8 text, starts with either { (for an object) or [ (for an array), and contains only the six JSON data types.

Use the JSON Formatter to pretty-print and validate any JSON, or the JSON Examples page to see real-world JSON samples you can copy and use.

JSON Data Types

JSON supports exactly six value types. Any valid JSON value must be one of these — no more, no less.

Note: JSON has no date type, no function type, and no undefined type. Dates are typically represented as ISO 8601 strings.

JSON Objects

A JSON object is an unordered collection of key-value pairs enclosed in curly braces {}. Each key is a string in double quotes, followed by a colon, followed by a value. Pairs are separated by commas — but no trailing comma is allowed after the last pair.

{
  "name": "Alice",
  "age": 30,
  "isAdmin": false,
  "score": 99.5,
  "address": null
}

Key rules for JSON objects:

• All keys must be strings in double quotes
• Keys should be unique within an object (duplicate keys are technically legal but behavior is undefined)
• The order of keys is not guaranteed
• Values can be any of the six JSON types
• No trailing comma after the last key-value pair

JSON Arrays

A JSON array is an ordered list of values enclosed in square brackets []. Values are separated by commas. Arrays can contain any mix of JSON value types.

["apple", "banana", "cherry"]

[1, 2, 3, 4, 5]

[true, false, null, 42, "mixed"]

[
  {"name": "Alice"},
  {"name": "Bob"}
]

Key rules for JSON arrays:

• Values are indexed starting at 0
• Order is preserved
• Can mix any JSON value types in one array
• No trailing comma after the last element

Nested JSON

JSON can be nested to arbitrary depth — objects can contain arrays, arrays can contain objects, and objects can contain objects. This is what makes JSON powerful enough to represent complex real-world data structures.

{
  "user": {
    "id": 101,
    "name": "Alice",
    "roles": ["admin", "editor"],
    "address": {
      "city": "New York",
      "zip": "10001"
    },
    "tags": [
      {"id": 1, "label": "premium"},
      {"id": 2, "label": "verified"}
    ]
  }
}

Use the JSON Viewer to explore nested JSON as a collapsible tree, making it much easier to navigate deeply nested structures.

JSON Formatting & Whitespace

JSON ignores whitespace (spaces, tabs, newlines) outside of string values. This means minified JSON and pretty-printed JSON are semantically identical — parsers treat them the same.

{
  "name": "Alice",
  "age": 30
}

{"name":"Alice","age":30}

Use pretty-printed JSON when debugging or in config files. Use minified JSON when sending data over a network to reduce payload size.

JSON vs XML vs YAML

JSON, XML, and YAML are all data serialization formats. Here's how they compare for common use cases:

Common JSON Use Cases

FAQ – JSON Format