Cadl is a language for describing cloud service APIs and generating other API description languages, client and service code, documentation, and other assets. Cadl provides highly extensible core language primitives that can describe API shapes common among REST, GraphQL, gRPC, and other protocols.
You can see some samples of this programming language on this online tool.
Cadl provides highly extensible core language primitives that can describe API shapes common among REST, OpenAPI, GraphQL, gRPC, and other protocols. Cadl is a design-first language that’s more maintainable and generates OpenAPI to take advantage of the ecosystem of available tooling.
You can read more about this on the devblogs Microsoft webpage.