Using this specification you will need to build a REST-service for validating JSON documents against JSON Schemas.
This REST-service should allow users to upload JSON Schemas and store them at unique URI and then validate JSON documents against these URIs.
Additionally, this service will "clean" every JSON document before validation: remove keys for which the value is null.
Client-side software as well as GUI is out of scope of this specification - user can choose any tool able to communicate via HTTP like curl
or write their own.