Hmmm, I'm not sure what you mean but doesn't providing a whois script accomplish the same thing? If you whois a domain and it comes up "blank," it must be available, likewise, if it comes up with info, it's taken.
You should know, that whois check will not always mean a name is available. Names take hours (upto 24) to reach the main registry that whois checks. You should warn your users, that results do not include names registered in the last 24 hours.