Atds is a program that generates a Scala interface from type definitions. In particular, given a set of ATD type definitions, this tool generates a set of Scala case classes representing those types with built-in JSON serializers. (Deserializers planned.)
The primary benefits of using the generated interface, over using a JSON library and writing case classes directly, are safety and ease of use when the same interface is needed in other languages.
Don't repeat yourself when defining a JSON interface in multiple languages. Instead generate compatible interfaces for all languages from a single definition.
Even if you're only using Scala, you may find the ATD definitions more concise and less boilerplaity than the equivalent Scala types. (Especially for sum types)