Arrays

Array value syntax — ordered, comma-separated collections of values.

An array is an ordered collection of values enclosed in square brackets. Arrays are containers used to express lists, sequences, and multi-dimensional tabular structures.

Each value in an array may be:

A scalar (string, number, boolean, null), or
A structured value (an object or another array).

Arrays are syntactically compact, support nesting, and avoid ambiguity by requiring every value to be present — trailing and elided elements are not allowed.

Syntax

An array begins with [ and ends with ], containing zero or more comma-separated values.

array = "[" [ value *("," value) ] "]"

Here, value is any valid Internet Object value, as defined in Value Representations. The syntax and behavior of each value type (strings, numbers, booleans, objects, arrays, null) is defined in its own page.

Structural characters

Symbol

Name

Unicode

Description

[

Open square bracket

U+005B

Starts an array

]

Close square bracket

U+005D

Ends an array

,

Comma

U+002C

Separates values within an array

Valid forms

[]                       # Empty array
[apple, banana, cherry]  # String values
[1, 2, 3]                # Number values
[T, F, N]                # Boolean and null values
[{x:1}, {y:2}]           # Array of objects
[1, [2, 3], [4, [5, 6]]] # Nested arrays
[[1,2],[3,4]]            # 2D array

Optional behaviors

Whitespace and formatting

Whitespace is permitted around elements and structural characters for readability.

[ a , b , c ]   # Valid

All forms with an equivalent value structure are interpreted identically.

Empty array

An empty array is written as a pair of brackets with nothing between them:

[]

This is a valid array with no elements.

Nesting

Arrays may contain other arrays, allowing arbitrarily deep structures.

[1, [2, 3], [[4]]]

Comments

Comments are allowed around and within arrays, following the format's general comment syntax.

[
  1, 2,  # inline comment
  3
]

Comments must not break value boundaries, and must not appear inside strings or object keys.

Invalid forms

A comma separates values, so every comma needs a value on each side of it:

[a, b, ]     # ✗ unexpected-token — trailing comma
[a,,c]       # ✗ unexpected-token — elided value
[ , ]        # ✗ unexpected-token — no value at all
[,a]         # ✗ unexpected-token — nothing before the comma

Missing separators are a different matter, and not an error:

---
[a b c]      # → ["a b c"] — one open string, not three values

An open string may contain spaces, so a b c is a single well-formed value and there is nothing for the parser to object to. See Syntax Errors for why this is the one place the format cannot help you.

Corrected versions

[a, b]       # ✓ valid
[a, null, c] # ✓ use null for a missing value

Preservation of structure

Internet Object preserves:

Value order
Whitespace (non-significant in interpretation)
Syntactic fidelity (as written)

It does not interpret:

The meaning of order
Whether values must be unique

Those semantics belong to the schema, the validator, or the application.