The Open Archives Initiative (OAI) is dedicated to solving problems of digital library interoperability by defining simple protocols, most recently the Open Archives Initiative Protocol for Metadata Harvesting [2], which was unveiled in January 2001. To support the adoption of this new interoperability technology, we have developed the Repository Explorer [1], a web-based tool to enforce compliance to the same interpretation of the protocol by the various different server implementations. This demonstration will show how the Repository Explorer can be used to perform either user-driven browsing or automatic testing of an implementation of the protocol.