A web service can provide a schema similar to a header file to define its API but there is no "standard" format for this schema, nor is there a standard location to look for such a thing.
You can of course provide your own schema. This tool lets you design an API for a web service in a popular schema format called OpenAPI.
You can of course provide your own schema. This tool lets you design an API for a web service in a popular schema format called OpenAPI.