Ensuring that ontologies are consistent is an important part of ontology development and testing. This is especially important when autonomous software agents are to use ontologies in their reasoning. Reasoning with inconsistent ontologies may lead to erroneous conclusions. In this paper we introduce the ConsVISor tool for consistency checking of ontologies. This tool is a consistency checker for formal ontologies, including both traditional data modeling languages and the more recent ontology languages. ConsVISor checks consistency by verifying axioms. ConsVISor is part of the UBOT toolkit that uses a variety of techniques such as theorem proving and logic programming. Some examples of the use of these tools are given.