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uniqueItems JSON Schema Keyword

Use uniqueItems to reject duplicate JSON values inside an array.

Array

Schema template

Try in Validator

JSON Schema

{
  "type": "array",
  "uniqueItems": true
}

Valid example JSON

[
  "admin",
  "editor"
]

Invalid example JSON

[
  "admin",
  "admin"
]

Fields

FieldTypeRequiredDescription
uniqueItemsbooleanYesWhen true, every array element must be unique by JSON value. Objects and arrays are compared structurally.

How to use this schema

Use uniqueItems for role lists, tags, IDs, and sets where repeated values would cause confusing behavior downstream.

Version support and combinations

This keyword or pattern is commonly supported across modern JSON Schema workflows. Check your validator for Draft-04, Draft-07, 2019-09, and 2020-12 behavior before relying on newer composition or conditional features.

Common combination: pair this reference with type, required, and properties so validation errors are specific enough for API clients and form users.

Batch validation seed

Want to validate JSON Schema in bulk? Toolumina Pro can grow into batch validation for 100+ files, saved schemas, and repeatable API contract checks.

Related reference pages

items JSON Schema KeywordUse items to define the schema that each element in an array must satisfy.minItems JSON Schema KeywordUse minItems to require an array to contain at least a minimum number of elements.contains JSON Schema KeywordUse contains when at least one array element must match a nested schema.