WSDL describes a pact between a client and a server so they can't screw it up. Comparing WSDL to WADL would make sense. JSON just describes objects in compact notation. Comparing JSON to XML would make sense when XML is only used to describe objects and nothing more. WSDL and WADL and HTML are all XML derivatives. WSDL and WADL could never exist or HTML for that matter if trying to use JSON to describe them since that's not what JSON was designed for.