The Six JSON Data Types

JSON has exactly six data types. Understanding these is the foundation of working with JSON. Every value in every JSON document is one of: string, number, boolean, null, object, or array. There are no dates, no functions, no undefined — if you need those, you represent them as strings or omit them entirely.

A sequence of Unicode characters wrapped in double quotes. Single quotes are not allowed. Use a backslash to escape special characters inside strings.

Common escape sequences:

• \" — double quote
• \\ — backslash
• \n — newline
• \t — tab
• \uXXXX — any Unicode character

"Hello, World!"

"She said \"hi\" and left."

"Path: C:\\Users\\alice"

Important: Dates are not a native JSON type. Store them as ISO 8601 strings like "2024-01-15T09:30:00Z".

An integer or floating-point number. No quotes. Scientific notation is valid. There is no separate integer vs float type in JSON — it is all just "number."

42

3.14

-100

1.5e10

Watch out: Very large integers (above 2^53) can lose precision when parsed in JavaScript. Use strings for large IDs.

Exactly two values: true or false. Both must be lowercase — True or TRUE are not valid JSON.

true

false

Represents the intentional absence of a value. Always lowercase null. It is distinct from an empty string "" or the number 0.

null

Use null when a property exists but has no meaningful value, such as "deletedAt": null for a record that has not been deleted yet.

An unordered collection of key-value pairs enclosed in curly braces {}. Keys must be strings. Values can be any of the six types, including other objects — enabling nested structures.

{
  "name": "Alice",
  "age": 30,
  "active": true,
  "address": {
    "city": "London",
    "zip": "EC1A 1BB"
  }
}

Key order is not guaranteed. Do not rely on insertion order when parsing JSON objects across different languages and parsers.

An ordered list of values enclosed in square brackets []. Array elements can be any type, and you can mix types (though keeping them uniform is a best practice).

["red", "green", "blue"]

[1, 2, 3, 4, 5]

[
  {"id": 1, "name": "Alice"},
  {"id": 2, "name": "Bob"}
]

{
  "username": "alice123",
  "score": 9850,
  "verified": true,
  "nickname": null,
  "tags": ["admin", "beta"],
  "profile": {
    "city": "London",
    "joined": "2022-03-15"
  }
}

Paste any JSON into the JSON Validator to confirm every value uses a valid type. The validator reports exactly which line contains an unsupported value so you can fix it immediately.