Background: Enteral tubes are prevalent among children with medical complexity (CMC), and complications can lead to costly health care use. Our objective was to design and test the usability of a mobile application (app) to support family-delivered enteral tube care. Methods: Human-centered design methods (affinity diagramming, persona development, and software development) were applied with family caregivers of CMC to develop a prototype. During 3 waves of usability testing with design refinement between waves, screen capture software collected user-app interactions and inductive content analysis of narrative feedback identified areas for design improvement. The National Aeronautics and Space Administration Task Load Index and the System Usability Scale quantified mental workload and ease of use. Results: Design participants identified core app functions, including displaying care routines, reminders, tracking inventory and health data, caregiver communication, and troubleshooting. Usability testing participants were 80% non-Hispanic white, 28% lived in rural settings, and 20% had not completed high school. Median years providing enteral care was 2 (range 1-14). Design iterations improved app function, simplification, and user experience. The mean System Usability Scale score was 76, indicating above-average usability. National Aeronautics and Space Administration Task Load Index revealed low mental demand, frustration, and effort. All 14 participants reported that they would recommend the app, and that the app would help with organization, communication, and caregiver transitions. Conclusions: Using a human-centered codesign process, we created a highly usable mobile application to support enteral tube caregiving at home. Future work involves evaluating the feasibility of longitudinal use and effectiveness in improving self-efficacy and reduce device complications.