What's the difference between an opaque token and a JWT (self-contained token) from the resource server's perspective?

An opaque token is a meaningless random string that the resource server must send to the Authorization Server's introspection endpoint to validate and learn its associated claims — this adds a network call per request but allows instant revocation. A JWT is fully self-contained and cryptographically verifiable locally (via signature check), requiring zero network calls per request, but cannot be instantly revoked before its natural expiry.