It's continuation of discussion from apigee-127/swagger-tools/issues/245. [Here](https://github.com/swagger-api/swagger-spec/blob/master/versions/2.0.md#schema-object) it said: > Unless stated otherwise, the property definitions follow the JSON Schema specification as referenced here. And I don't see any requirements for `items` inside `Schema object`. But JSON Schema treat `items` as optional field.