Purpose: The purpose of this presentation is to reveal usability testing results of a web-based electronic clinical decision support (ECDS) tool developed to promote and guide critical thinking towards the differential diagnosis of dizziness. Description: Innovative, responsive, and clinically relevant support tools are useful adjuncts to physical therapy education curriculum and the development of clinical competency. Engaging students and clinicians in self directed critical thinking activities promotes professional development, pattern recognition, and skill in hypothesis development leading to Physical Therapy diagnoses. DizzyDx is a mobile web application designed to assist physical therapy students and clinicians in creating a prioritized list of impairments, leading to the development of an evidence-supported and case-specific differential diagnosis for the perception of dizziness. The app includes multiple sensory system categories, neurological and musculoskeletal considerations, autonomic and immune considerations, direction toward appropriate testing, supporting best evidence, and indicators that would suggest the need for multidisciplinary consultation or referral. Summary of Use: Five students enrolled in Doctorate level physical therapy education engaged in usability testing based upon a video of a real patient interview. A User Experience (UX) Designer performed a heuristic study, monitored in-person screen and audio-visual recordings of participants, administered a usability questionnaire, and collected analyzed data. The results of the study will guide future iterations of app development and determine readiness for product launch. Importance to Members: Dizziness is an elusive and invisible problem often associated with vestibular and cardiovascular disorders. It is a poor prognostic factor following head and neck trauma and can co-exist in many complex autoimmune and neuroinflammatory disorders. Up to 80% of individuals who seek medical care for symptoms of dizziness receive no explanatory diagnosis. Consumer demand for information related to effective diagnosis and management of dizziness is substantial, with an estimated > 1,000,000 global Google searches per month, and > 500,000 per month in the US alone. Unlike medical algorithmic models, the DizzyDx app does not produce a diagnosis, but rather promotes critical thinking skills a therapist uses to arrive at an actionable diagnosis. The app represents content developed for vestibular and concussion management workshops where clinician and student participants expressed strong interest in access to the tool to reinforce clinical decision making. Ongoing usability testing comparing user experience between physical therapy students, faculty from physical therapy programs, and practicing physical therapy clinicians will determine the clinical usefulness and perceived clinical value of DizzyDx. Ultimately DizzyDx is intended to support autonomous practitioners’ level of critical thinking required for the evaluation and management of challenging subjective complaints of dizziness.