I maintained a domain database and normalised to ASCII with libidn, sometimes the input data was not from zone files and preferably would've been able to double

I maintained a domain database and normalised to ASCII with libidn, sometimes the input data was not from zone files and preferably would've been able to double check the characters used in a potential domain to ensure it's something that's registerable, without any network required. That was my motivation for looking into the topic originally.