As the quality of ontologies plays an important role in supporting semantically-enabled applications, defining concepts as well as their relations correctly and completely is crucial when developing an ontology. In this paper we introduce a Protégé plugin for extending ontologies, which guides Protégé users through the addition of new concepts as well as their instances and axioms in which they participate in a semiautomatic way. Furthermore, the tool suggests additional subsumption axioms that a user can validate and, if appropriate, add to the ontology to make the ontology more complete.