Schema languages for "REST" exist (OpenAPI, RAML), and many people use them, but they certainly haven't taken off to the extent that WSDL did. I find that odd.

Schema languages for "REST" exist (OpenAPI, RAML), and many people use them, but they certainly haven't taken off to the extent that WSDL did. I find that odd. The new hotness is gRPC, which is based on protocol buffers, which uses an out-of-band schema file (you can do a certain amount with protobufs without a schema file, but nothing very useful). People appear to be happily adopting that, and aren't complaining about the need for a schema.