This article presents the usability evaluation of an e-learning web application that supports students in self-directed learning of key competences and soft skills during project phases. We developed “clavis” based on an open-source learning management system and optimized it for mobile access to microlearning content. The usability evaluation explores how students interact with the learning environment using predefined interaction scenarios and questionnaires. We used thinking aloud, observation and an interaction recording to assess the usability from the students’ point of view. Our article compares the evaluation results of desktop and mobile interface and discusses problems with the hybrid use of browser- optimized learning management systems on mobile devices.