JsonWhois.io - JsonWhois is the leading cloud hosted Whois API.
WhoisAPI - WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses...
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
ICANN WHOIS - The official ICANN WHOIS search for domain lookups.
DNSdumpster.com - Open source domain intelligence lookups for security recon
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.