This month, the German Digital Library (Deutsche Digitale Bibliothek - DDB) made a promising step towards the further openness of their data by providing an API for users. This API provides access to all DDB metadata published under a license of CC0, which is predominant in their materials. Publishing this API provides many opportunities for users to create applications, combine with other data, or incorporate German digital heritage on other platforms. In the future, DDB also plans to hold a programming competition for API applications as well as a series of workshops for developers.
And, of course, we must not forget that API exists in many digital state libraries. For example, there is an API at the Australian National Library in many of their projects , as well as a library of congress in the form of a Search and Retrieve API .