Of course, there are tons, they're generally called IDLs (interface description languages), common examples are Protobufs, Avro, Thrift, etc. They're not hugel

Of course, there are tons, they're generally called IDLs (interface description languages), common examples are Protobufs, Avro, Thrift, etc. They're not hugely popular for web services largely because the web was designed to avoid exactly this kind of a priori contractual requirements between communicating parties. But that's a much bigger conversation.