Today’s online model repositories offer to download and view the textual specifications of e.g. metamodels and models in the browser. For users, in order to efficiently search a model repository, a graphical visualization of the stored models is desirable. First attempts that automatically generate class diagrams as bitmaps, however, do not scale for large models and fail to present all information. In this paper, we present our Web 2.0 MetaModelbrowser, a model visualization service which provides an Ajax-based tree-viewer for efficiently browsing Ecore-based metamodels and their models. As a main contribution of this work the MetaModelbrowser is complementary to existing model repositories in that its visualization service can be integrated into them. The MetaModelbrowser, furthermore, allows zooming in and out of the details of arbitrarily sized models as necessary. Furthermore, we have done some case studies on the one hand how to extend the MetaModelbrowser, e.g., for creation, update, and deletion of model elements as well as supporting model weaving, and on the other hand how to incorporate the MetaModelbrowser in current versioning systems.