uniqueItems : Boolean

uniqueItems

Boolean

If this keyword is set to the boolean value true, the instance validates successfully if all of its elements are unique.

Value This keyword must be set to a boolean value Hint: Use the jsonschema metaschema and jsonschema lint commands to catch keywords set to invalid values
Kind Assertion
Applies To Array
Base Dialect Draft 7
Changed In None
Introduced In Draft 2
Vocabulary Validation
Specification https://json-schema.org/draft-07/draft-handrews-json-schema-validation-01#rfc.section.6.4.5
Metaschema http://json-schema.org/draft-07/schema#
Official Tests draft7/uniqueItems.json
Default false
Annotation None
Affected By None
Affects None
Also See

When set to true, the uniqueItems keyword restricts array instances to items that only occur once in the array. Note that empty arrays and arrays that consist of a single item satisfy uniqueness by definition.

Remember that JSON Schema is a constraint-driven language. Therefore, non-array instances successfully validate against this keyword. If needed, make use of the type keyword to constraint the accepted type accordingly.

Examples

A schema that constrains array instances to not contain duplicate items Schema 
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "uniqueItems": true
}
Valid An array value without duplicate items is valid Instance 
[ 1, "hello", true, { "name": "John" } ]
Invalid An array value with duplicate elements is invalid Instance 
[ { "name": "John" }, 1, "hello", true, { "name": "John" } ]
Valid An empty array value is valid Instance 
[]
Valid A non-array value is valid Instance 
"Hello World"
A schema that allows array instances to contain duplicate items Schema 
{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "uniqueItems": false
}
Valid An array value without duplicate items is valid Instance 
[ 1, "hello", true, { "name": "John" } ]
Valid An array value with duplicate elements is valid Instance 
[ { "name": "John" }, 1, "hello", true, { "name": "John" } ]
Valid An empty array value is valid Instance 
[]
Valid A non-array value is valid Instance 
"Hello World"