The rapid growth of mobile applications and higher ergonomic requirements demand affordable tools for objective user-behavior analysis without the need for costly laboratory equipment. This paper presents a conceptual methodology for assessing mobile UI usability through eye-tracking that relies solely on a smartphone’s front-facing camera. Users view static app screens, and their gaze is captured with the camera and analyzed via key metrics, such as time to first fixation, fixation duration, fixation frequency, and scan path. These data reveal attention-attracting or overlooked elements and areas of cognitive load, enabling rapid, reliable comparison of diverse design variants during iterative prototyping and redesign processes. Leveraging built-in smartphone capabilities minimizes costs and makes eye-tracking studies accessible to a wide range of professionals, including researchers, designers, educators, and usability specialists, thereby supporting the integration of objective design assessment into digital product development workflows. The paper outlines staged procedures from preparation and planning to interpretation and implementation, and it recommends secure local processing with transparent disclosure of data use.