The Whois Tool is meant to help you find out information about a domain, like who owns it, name servers and other information.

It's basicaly a protocol used to query databases for various information ( domains, IP blocks, AS systems and others ).

The whole protocol is documented in RFC 3912 and wikipedia.

You can use this to query specific whois servers if you're wondering about information about new .tld's.

You can use the api to query curl https://serverstuff.info/api/whois?host=<query>&whoishost=<server> the [whoishost] part is optional.