Neat. I thought for a moment it was just a script embedded in a TXT record, but you do communicate over DNS with a server-side implementation of the game. The perl bit is just to unescape the response.
It uses a custom DNS server that returns the result as a TXT record for the domain <your guess>.wd.ip.wtf. You don't need to point directly at that server as it's registered as the nameserver for that domain.
It uses a custom DNS server that returns the result as a TXT record for the domain <your guess>.wd.ip.wtf. You don't need to point directly at that server as it's registered as the nameserver for that domain.