BEACON: an efficient SAT-based tool for debugging ℰℒ + ontologies. Description Logics (DLs) are knowledge representation and reasoning formalisms used in many settings. Among them, the ℰℒ family of DLs stands out due to the availability of polynomial-time inference algorithms and its ability to represent knowledge from domains such as medical informatics. However, the construction of an ontology is an error-prone process which often leads to unintended inferences. This paper presents the BEACON tool for debugging ℰℒ + ontologies. BEACON builds on earlier work relating minimal justifications (MinAs) of ℰℒ + ontologies and MUSes of a Horn formula, and integrates state-of-the-art algorithms for solving different function problems in the SAT domain.