JsonWhois.io - JsonWhois is the leading cloud hosted Whois API.
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
EZwhois - Whois domain information such as registrar, domain status, expiration date, and name servers.
DNSdumpster.com - Open source domain intelligence lookups for security recon
WebCargo - Optimize your workflow by offloading it to us. Useful API's with seamless integration that scale to your needs.