In this paper we describe a web-based tool that supports the human in revising ontology alignments. Our tool uses logical reasoning as a basis for detecting conflicts in mappings and exploits these conflicts to propagate user decision. The proposed approach reduces the effort of the human expert and points to logical problems that are hard to find without support. 1 Motivation The alignment of ontologies is a common problem on the semantic web as many tasks such as information integration or semantic search rely on integrated background knowledge. As manual ontology alignment is a difficult and timeconsuming process, a variety of algorithms and systems for computing matches between elements of different ontologies have been developed [2]. Almost all of these methods rely on linguistic or structural heuristics for deciding whether to regard elements from different ontologies as equivalent or not. These heuristics are bound to fail in many situations resulting in erroneous mappings...