JSON Schema for OpenAPI course

Looking to master JSON Schema for OpenAPI?

A 9+ hour course taught by a member of the JSON Schema Technical Steering Committee

Take the Video Course Also check out our O'Reilly book

additionalItems : Schema | Boolean

additionalItems

Schema | Boolean

If items is set to an array of schemas, validation succeeds if each element of the instance not covered by it validates against this schema. If set to false, no additional items are allowed in the array instance.

Value This keyword must be set to a valid JSON Schema Hint: Use the jsonschema metaschema and jsonschema lint commands to catch keywords set to invalid values
Kind Applicator
Applies To Array
Base Dialect Draft 4
Changed In None
Introduced In Draft 3
Vocabulary Validation
Specification https://json-schema.org/draft-04/draft-fge-json-schema-validation-00#rfc.section.5.3.1
Metaschema http://json-schema.org/draft-04/schema#
Official Tests draft4/additionalItems.json
Default {}
Annotation None
Affected By
Affects None
Also See

The additionalItems keyword restricts array instance items not described by the sibling items keyword (when items is in array form), to validate against the given subschema.

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 start with a boolean item followed by a number item, with only string items allowed beyond that Schema 
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "items": [ { "type": "boolean" }, { "type": "number" } ],
  "additionalItems": { "type": "string" }
}
Valid An array value that consists of a boolean item followed by a number item is valid Instance 
[ false, 35 ]
Valid An array value that consists of a boolean item followed by a number item and string items is valid Instance 
[ false, 35, "foo", "bar" ]
Invalid An array value that consists of a boolean item followed by a number item and non-string items is invalid Instance 
[ false, 35, { "foo": "bar" } ]
Valid An empty array value is valid Instance 
[]
Valid A non-array value is valid Instance 
"Hello World"
A schema that prevents additional items beyond the tuple Schema 
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "items": [ { "type": "boolean" }, { "type": "number" } ],
  "additionalItems": false
}
Valid An array value with exactly two items matching the tuple is valid Instance 
[ false, 35 ]
Invalid An array value with items beyond the tuple is invalid Instance 
[ false, 35, "foo" ]
A schema that describes open items and additional items leads to the additional items schema being ignored Schema 
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "items": { "type": "number" },
  "additionalItems": { "type": "string" }
}
Valid An array value with only numbers is valid Instance 
[ 1, 2, 3 ]

Valid An array value with numbers and strings is valid as the keyword is ignored Instance 
[ 1, 2, "foo" ]
A schema with only additional items definitions leads to the additional items schema being ignored Schema 
{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "additionalItems": { "type": "string" }
}

Valid Any array is valid Instance 
[ 1, 2, 3 ]
Valid A non-array value is valid Instance 
"Hello World"