JSON arrays — syntax, examples, and common mistakes

A JSON array is an ordered list of values enclosed in square brackets. Arrays can contain any mix of JSON value types and are zero-indexed like arrays in most programming languages.

Syntax rules

[value, value, value]

• Square brackets wrap the array: [ and ]
• Values are separated by commas
• No trailing comma after the last value
• Values can be any JSON type: string, number, boolean, null, object, or another array
• Whitespace (spaces, tabs, newlines) between values is allowed and ignored

Examples

// Array of strings
["apple", "banana", "cherry"]

// Array of numbers
[1, 2, 3, 4, 5]

// Mixed types (valid JSON)
["Ada", 30, true, null, {"role": "engineer"}]

// Empty array
[]

// Nested arrays (matrix)
[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

// Array of objects (the most common API pattern)
[
  {"id": 1, "name": "Ada"},
  {"id": 2, "name": "Linus"},
  {"id": 3, "name": "Grace"}
]

Accessing array elements

// JavaScript
const tags = JSON.parse('["json", "api", "rest"]');
tags[0];        // "json"
tags.length;    // 3
tags[tags.length - 1]; // "rest"

// Nested
const matrix = JSON.parse('[[1,2],[3,4]]');
matrix[1][0];   // 3

// Python
import json
tags = json.loads('["json", "api", "rest"]')
tags[0]         # "json"
tags[-1]        # "rest"  (Python negative indexing)

Common mistakes

Trailing comma

// ✗ Invalid — trailing comma after last element
[1, 2, 3,]

// ✓ Valid
[1, 2, 3]

Using single quotes

// ✗ Invalid
['apple', 'banana']

// ✓ Valid — double quotes only
["apple", "banana"]

Missing comma between elements

// ✗ Invalid
["apple" "banana"]

// ✓ Valid
["apple", "banana"]

Arrays vs objects in JSON APIs

Use an array when the response is a list of items with no meaningful key. Use an object when you need named fields or metadata alongside the list.

// Array response — a list of users
[{"id":1,"name":"Ada"}, {"id":2,"name":"Linus"}]

// Object response — metadata + data
{
  "total": 2,
  "page": 1,
  "users": [{"id":1,"name":"Ada"}, {"id":2,"name":"Linus"}]
}