Open Library

Open Library, run by the Internet Archive, is an ambitious effort to build one web page for every book ever published. Behind those pages sits an open, editable catalogue of more than 20 million records, assembled from library systems, publishers, and readers, covering works, editions, authors, subjects, publication dates, identifiers such as ISBNs, and cover images. For a large slice of titles it also runs controlled digital lending, where one borrower reads one scanned copy at a time.

The metadata is what makes it useful for RAG. You can query it live through a public REST API (search, works, editions, and author endpoints returning JSON), or, better for large jobs, download the monthly bulk data dumps of the whole catalogue rather than crawling the API. The dumps are big line-delimited files, so plan to stream and filter them down to the fields you actually need. A passage per book (title, author, subjects, and a one-line summary) gives clean, factual chunks to ground a system in bibliographic detail.

It is best for anything that reasons about books as objects: recommendation tools, catalogue enrichment, reading assistants, or a layer that resolves fuzzy references to real editions and identifiers. If you need dependable answers about who wrote what, in which edition, and when, this is a strong backbone.

Keep the split between metadata and content clear. The catalogue records are released under CC0, placing them in the public domain, so you can reuse them freely with no attribution required. Full text, however, sits under the lending programme and is not open for reuse: you cannot treat the scanned books as an open text corpus. Record quality also varies, since it is community-edited, so duplicate editions and patchy fields show up and are worth deduplicating.

For actual public-domain full text, pair Open Library with Project Gutenberg or the wider Internet Archive; use Open Library itself when what you want is rich, freely reusable book metadata at scale.