Obesity-related knowledge and functional requirements were extracted from clinical practice guidelines, a literature review, and consultations with experts. The extracted knowledge was used to design obesity-management algorithms, and the functions of the developed app are presented through a use case diagram and activity diagrams. The database and user interface were designed and then an app was developed. The proficiency and efficiency of the algorithm were evaluated using scenarios, while the user interface was assessed using a mobile heuristics evaluation tool, with its usability determined using the Post-Study System Usability Questionnaire.