I always wonder, how do sites like this get their list of books and book metadata? Do publishers have an API? What about Amazon?
It is so bad!!! I use Nielsen's API, but the data is pretty rough, and you have to spend a lot of time cleaning it. Plus, the archaic industry standards around genre are hard to translate to what readers use - https://www.bisg.org/complete-bisac-subject-headings-list . Ingrams and Bowker are the other big metadata providers. Ingram's is good but expensive, but the data faces the same issues.
I imagine it complements or my even supersede tags.
(Admit I haven’t looked at all the sites people are mentioning in the comments yet- lots of good leads!)