The International Standard Book Number is a unique identifier for books.
It was introduced in 1970 and currently has 13 numbers.
This, for example, is the ISBN for Microcavities: (ISBN: 978-0198782995) (through template {{ISBN|978-0198782995}}).
I need to write a script isbn2bib similar to doi2bib so as to archive books (since 19:00 on 23 August (2024)).
isbndb appears to be what I need but it is a paying service (it has an academic/educational plan of ~$7 per month).