JSON has exactly six data types. Unlike programming languages, which usually have dozens of types (integer, float, date, etc.), JSON keeps a very lean set. This post lists each one quickly, with syntax and important notes.
String
Text, always in double quotes.
"any text"Special characters inside a string need to be escaped: double quotes (\"), backslash (\\), line break (\n), among others.
Number
Numbers, without quotes. JSON doesn’t distinguish integers from decimals (floats) in its syntax, both are just “number.”
42
3.14
-7
1.5e10Some formats aren’t accepted: a leading zero (01), a decimal point with no digit before (.5) or after (5.) it.
Boolean
Only two possible values, without quotes.
true
falseNull
Represents the absence of a value, without quotes.
nullWorth noting null is different from a key simply not existing in the object. {"age": null} means the field exists, but is empty; an object without the age key means the field wasn’t provided at all.
Object
A collection of key-value pairs, delimited by curly braces {}.
{"name": "Ana", "age": 30}Array
An ordered list of values, delimited by square brackets [].
["item1", "item2", "item3"]Types that do NOT exist in JSON
Worth highlighting what isn’t a valid type, since this tends to confuse people coming from other languages.
undefined: exists in JavaScript, not in JSONNaNandInfinity: exist in JavaScript, not in JSON- Date: there’s no native date type; dates are usually represented as strings in a specific format (like ISO 8601:
"2026-01-15T10:00:00.000Z") - Functions: JSON represents data, not executable code
Summary table
| Type | Syntax | Example |
|---|---|---|
| String | In double quotes | "text" |
| Number | No quotes | 42, 3.14 |
| Boolean | No quotes | true, false |
| Null | No quotes | null |
| Object | In curly braces | {"key": "value"} |
| Array | In square brackets | ["a", "b"] |
If you’re unsure whether a specific value is a valid type in JSON, paste the content into JSON Validator to confirm.