It's a good question! For any use case where there is a set of servers and a set of clients that interact with those servers, you often end up having to hard-c

It's a good question! For any use case where there is a set of servers and a set of clients that interact with those servers, you often end up having to hard-code API contracts and response shapes on each client and each server. If your client and server are written in the same language, you might be able to write an interface/class once and share the code between both builds. But what if (as is more often the case) they are written in different languages? What if you introduce a 3rd client, written in a 3rd language (say C# on the server, Swift on iOS, and Java on Android)? This is what Google uses Protobuf for [0]. A competing solution is JSONSchema, which gives a slightly different set of functionality than Protobuf. You describe your interface once with JSONSchema, and compile it into interfaces/classes for your various clients/servers to consume. This gives you compile time safety, and eliminates the need to manually author these classes and manually keep them in sync between platforms. As you scale up the number of services/clients/servers you're running, a system like this becomes not just helpful, but necessary to ensure that they can all talk to one another. [0] https://developers.google.com/protocol-buffers/ https://developers.google.com/protocol-buffers/