I've had them listed on our domain tools for a spell: Domain Name Tools
I like how it turns red when you type a domain and it's taken but I have found a number of inconsistencies where it says a domain is taken and it is actually not. So I don't know how they collect their data but I can assure you the domains they have marked as taken are not always taken.
I like how it turns red when you type a domain and it's taken but I have found a number of inconsistencies where it says a domain is taken and it is actually not. So I don't know how they collect their data but I can assure you the domains they have marked as taken are not always taken.
Likely they use the zonefiles in order have a local lookup database and then do a full check later. It would be interesting to look at some examples to get a better idea. There's some delay in zonefile updates, at least 24 hours. I can also think of a number of cases where domains would show as available, but might be registered or blocked.