JSON Syntax Rules

The 6 JSON Value Types

A JSON value must be exactly one of these six types:

"Hello, world!"

42

true / false

null

{"key": "value"}

[1, "two", true]

String Rules

Strings are the strictest part of JSON syntax. The rules:

• Double quotes only: Strings must be wrapped in double quotes. Single quotes are not valid JSON: 'hello' is invalid, "hello" is valid.
• Escape special characters: Certain characters inside strings must be escaped with a backslash: \" (quote), \\ (backslash), \n (newline), \t (tab), \r (carriage return), \/ (forward slash).
• Unicode escapes: Any Unicode character can be represented as \uXXXX where XXXX is the four-digit hex code.
• No raw control characters: Control characters (ASCII 0–31) must be escaped. You cannot include a raw newline or tab inside a string.

// Valid string examples
"Simple string"
"String with \"quotes\" inside"
"Line one\nLine two"
"Tab\there"
"Unicode: \u0041"  // = "A"

Number Rules

0
42
-7
3.14
1.5e10
2.5E-3

NaN
Infinity
0x1F      (hex)
077       (octal)
+42       (leading +)
.5        (leading dot)

Numbers cannot have leading zeros (except 0.5). NaN and Infinity are JavaScript concepts — they are not part of JSON.

Object Rules

• Keys must be strings in double quotes
• Key-value pairs are separated by a colon :
• Multiple pairs are separated by commas
• No trailing comma after the last pair
• No duplicate keys (technically allowed by spec but discouraged — parsers may ignore duplicates)
• Order of keys is not guaranteed

{
  "name": "Alice",
  "age": 30,
  "active": true,
  "address": {
    "city": "New York"
  }
}

Array Rules

• Values are wrapped in square brackets [ ]
• Values are separated by commas
• No trailing comma after the last element
• Values can be of any valid JSON type — including mixed types
• Arrays can be empty: []
• Arrays can be nested: [[1, 2], [3, 4]]

[
  "string",
  42,
  true,
  null,
  {"nested": "object"},
  [1, 2, 3]
]

Whitespace & Formatting

Whitespace (spaces, tabs, newlines) is ignored between tokens in JSON. Both of these are identical to a parser:

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

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