Sunfish allow plugin creation too add more functionality through service types.
For details see Sunfish Text Plugin solution.
Create a new C# library project, the assembly name should start with "sf-" and use Sunfish.exe as reference. If the Sunfish reference is set as project, also copy the $sunfish directory
If the resulting assemlby is not a .dll and not starts with sf- Sunfish will not load it.
Also is hight recomendable to set the startup program on debug as the Sunfish.exe inside bin/debug folder.
Create a class that inherits SunfishService and implement Process method.
The call object contains methods for accessing request and response.
Place the plugin on the same path ans sunfish.exe
Newtonsoft's Json.NET is available for plugins.