Array Items Schema — Uniform Type Validation

Uniform Array Item Validation

The items keyword defines a schema that every element in the array must satisfy. This is the most common way to validate arrays — ensuring all elements share the same type and constraints.

Basic Syntax

{
  "type": "array",
  "items": {
    "type": "string",
    "minLength": 1
  }
}

Every element in the array must be a non-empty string. An empty array [] also passes because there are no elements to violate the constraint.

How the Example Schema Works

The schema defines three arrays with different item types:

1. userIds — an array of positive integers. The items schema requires each element to be an integer with minimum: 1. The array itself must contain 1 to 100 elements. The test value [101, 202, 303, 404] passes — four positive integers.

2. emails — an array of email strings. Each element must satisfy format: "email". The test value contains two valid email addresses.

3. coordinates — an array of coordinate pairs. Each element is itself an array of exactly two numbers (enforced by minItems: 2 and maxItems: 2). This creates a list of [latitude, longitude] pairs. The test value contains two valid coordinate pairs.

Nested Arrays

The coordinates field demonstrates nested array validation. The outer items schema is itself an array schema:

{
  "type": "array",
  "items": {
    "type": "array",
    "items": { "type": "number" },
    "minItems": 2,
    "maxItems": 2
  }
}

This pattern is useful for matrices, GeoJSON coordinates, and any two-dimensional data structure.

items vs. contains

• items — every element must match the schema.
• contains — at least one element must match the schema.

{
  "type": "array",
  "contains": { "type": "string", "const": "admin" }
}

This requires the array to contain at least one "admin" string, but other elements can be anything. Use contains when you need to assert the presence of a specific value without constraining all elements.

Empty Arrays

By default, an empty array [] passes items validation because there are no elements to check. Use minItems: 1 if you need at least one element. This is a common gotcha — forgetting minItems allows empty arrays to slip through.