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xISBN (Web service)

Use this Web service to map book-related identifiers (ISBN, LCCN, OCLC number), based on WorldCat information. Free and subscription versions are available.

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xISBN Web service

The xISBN Web service supplies ISBNs and other information associated with an individual intellectual work that is represented in WorldCat. Submit an ISBN to this service, and it returns a list of related ISBNs and selected metadata. The service is based on WorldCat, the world's largest network of library content and services. Current xISBN database covers 23,227,419 ISBNs.

We also support other books-related identifiers mapping, such as xOCLCNUM as part of xISBN service.

How xISBN works

ISBNs are related to each other using librarian-catalogued bibliographic records in WorldCat with an algorithm developed by OCLC Research. The algorithm restructures WorldCat bibliographic records to conform to the FRBR conceptual model for information objects. For instance, rather than requiring an end user to traverse multiple records that represent many different manifestations of a book—including printings, hardback or paperback editions or even filmed versions—"FRBRized" WorldCat information allows that user to review a core record that lists all manifestations.

The xISBN Web service queries database tables in WorldCat created by the FRBR algorithm.

Using the xISBN Web service

To use the service, you submit a single, known ISBN value embedded in a URL to the xISBN server, and the server returns a list of associated ISBNs and relevant metadata. The ISBNs are sorted by the number of times each represented item is held by a WorldCat library, highest to lowest. Therefore, the first returned ISBN represents the most-held item in WorldCat among all associated items.

You may receive associated ISBNs in either XML, XHTML, Python, JSON, or Ruby format. The xISBN server supports REST-based requests as well as the OpenURL and unAPI protocols.


The xISBN Web service is free for non-commercial use when usage does not exceed 1000 requests per day. Free usage is governed by the WorldCat Affiliate Terms and Conditions. See the xISBN API for instructions.

The xISBN Web service is free to all OCLC cataloguing members after subscription.

The service is also available on a subscription basis for commercial use or non-commercial usage that meets or exceeds 1000 requests per day. Subscription-based use is available in two types:

  1. Access by cumulative total
    It enables a specific number of queries (e.g. 100,000 accesses) that have no time limits or expiration date.
  2. Daily access limit
    It allows a specific number of queries (e.g. 1,000 accesses) per day.

How to subscribe

You must first create a WorldCat Affiliate account. Have one already? Sign in to place an order. For technical support, Please contact us at