REST is a design principle, not a protocol. As such you can make a REST system discoverable via e.g. external schemas (commonly OpenAPI) or self-documentation

REST is a design principle, not a protocol. As such you can make a REST system discoverable via e.g. external schemas (commonly OpenAPI) or self-documentation but there is no guarantee that either exists, and while the latter is intrinsic there is no standard discovery mechanism for the former (cf openapi-specification issues 724 or 2128).