From the RePEc Blog:
RePEc is all about the dissemination of its metadata on the economics research literature, and another means of dissemination has been added to its portfolio: an API (Application Programming Interface).
As we have yet to learn how much demand there is and how it will load our servers, the use of the API is restricted at this point. We want to encourage data user to first use the traditional method to gather RePEc data, as described in this document, before applying for an API user code. Note that functionalities are getting added to the API as users demand, thus not everything is possible at this point.