Motivation -- Evaluation of the visual design and cognitive ergonomics of teaching ontologies. Research approach -- The underlying research framework is pursuing one method, where clarity and harmony of teaching ontology are evaluated by assessing its structure with several quantitative metrics. Findings/Design -- The method represents an 8-step methodology where different parameters of an ontology are assessed. An application was developed that helps experts during the evaluation process by utilizing automatic metric values calculating. Research limitations/Implications -- Such an approach is feasible for ontologies that are used by people for education or knowledge sharing; it is not applicable for evaluating ontology performance in the software applications. Originality/Value -- This method will practically aid the process of knowledge structuring and ontology design. Take away message -- The main characteristic of "good" teaching ontology is its harmony.