I am not so sure what you mean exactly but this is my stack.
I use pure Zinc-REST on the Gemstone side and the REST API is
described in Swagger-Spec from within Gmestone.
Clients are VBA, Amber and Pharo and they utilize the Swagger API
spec to access the server.
Works pretty well and is much more preformant than the intial Pharo
MongoDB backend I initially used.
Have a look into
http://smalltalkhub.com/#!/~HeSe/Swagger-Spec
There you can find most of the needed Swagger implementation some
minor details like type constants are missing.
Once your Gemstoneserver knows how to host his Swagger-Spec you can
host it via
https://github.com/swagger-api/swagger-ui
This saves a lot of explaning time to client developers.