books
WorldCat / OCLC
The world's largest union catalogue of library holdings, aggregating more than 550 million records and showing which libraries hold a given item. You search it through the web interface at search.worldcat.org. There is no longer a free API, so use the website, it remains the reference standard for locating a physical copy in a library.
No programmatic check, opens the archive’s own search.
Why it’s useful & how it works
WorldCat is the definitive tool for answering one question: which library near you holds a particular book. It aggregates holdings from more than 10,000 libraries worldwide, so a search surfaces not just whether a book exists but exactly where physical or digital copies are held, enabling interlibrary loan requests. There is no free API, so Echo links you to the search.worldcat.org website, where you search by title, author, ISBN, or OCLC number and filter by library location or format.
What’s inside
More than 2.7 billion item holdings drawn from over 10,000 member libraries globally, representing the broadest union catalogue of physical and digital library collections in existence.
What we measured
Our own probes, not the archive’s own claims. Re-run periodically; every reading below is dated.
Reachability
- Direct request
- Responded HTTP 200 597 ms
- Through a datacenter proxy
- Responded HTTP 200 1.1 s
- API, direct
- Not found HTTP 404 232 ms
- API, through a proxy
- Not found HTTP 404 573 ms
Reachability measured 2026-08-22.
Access
Catalogue link only, open the archive to search it yourself.