Here I have compiled three of the easiest to use REST services to check a domain WHOIS information. Some also provide extra services as check domain availability, take a screenshot of the site, check if email address is valid... All those actions are available as actions that simply ask for the domain and api key (you need to register with the sites). It has a total of 13 Application Objects, but you can drop most of them if you're sticking with a single provider.