Open Library
Open Library, run by the Internet Archive, aims to create a single page for every book ever published. It combines catalogue records from libraries, publishers, and readers into an open, editable database of authors, editions, subjects, and covers. For many titles it also offers controlled digital lending, where one reader borrows one copy at a time.
The metadata is the main draw for RAG. You can query it through a public API or download bulk data dumps, which makes it useful for building book recommendation tools, enriching library catalogues, or grounding a system in bibliographic facts. Full text is available for some works but is subject to lending terms rather than open reuse.
The catalogue metadata is released under CC0, placing it in the public domain, so you can reuse the records freely. Full-text access is governed separately by the lending programme.
Related sources
Google Books Ngrams
Word and phrase frequency data drawn from Google's digitised book collection, spanning centuries of published text. It counts how often words and short phrases appear by year, which is useful for historical language analysis and time-aware RAG features.
LibriVox
A volunteer project providing free public domain audiobooks. Volunteers record themselves reading works whose copyright has expired, which makes it a handy source of speech data for training speech-to-text models and building multimodal RAG.
Project Gutenberg
A volunteer effort to digitise and archive public domain books, with more than 70,000 free ebooks. Mostly English, but it covers many languages. One of the oldest digital library projects, so it is a clean, permissively licensed source of full-text literature for RAG.
Standardized Project Gutenberg Corpus (SPGC)
A research-ready version of the Project Gutenberg catalogue with consistent formatting, tidy metadata, and token counts for every book. It saves you the cleanup work, so you get uniform full-text literature ready to chunk and embed for RAG.