books
Google Books API
Google's index of book volumes, covering tens of millions of titles with metadata and, where permitted, previews. You can search by title or ISBN through its API, and a free key raises the otherwise tight request quota. It offers broad coverage for confirming a book's existence and edition details and for finding preview pages.
Books API
Why it’s useful & how it works
Keyless allowed but per-IP quota hit fast (429 direct); proxies errored. Add a free Google Cloud key and route direct. JSON.
What’s inside
Tens of millions of volumes.
API access
Access
Programmatic API access (a key may be required — see the API tag).