ABSTRACT Objectives: to assess the usability of an app prototype for diabetic foot self-care by an end user. Methods: a descriptive study that uses heuristic assessment of a hybrid app usability. Fifteen users of an outpatient diabetes care service in a capital of Northeastern Brazil participated in the study during April 2018. The usability measurement tool called Smartphone Usability questionnaiRE was applied. Results: the lowest score was 77 and the highest was 112, with an average usability of 96.1 points. Usability was framed in the last two levels, 70 and 8o. Users now strongly agree (level 70) and fully (level 80) with the assessed items, which represents good usability of the apps prototype. Conclusions: the final product developed focuses on user needs and requirements, which can ensure usability based on effectiveness, efficiency and satisfaction triad.