Objectives: We aimed to develop and test a tool to engage parents of febrile infants ≤ 60 days of age evaluated in the emergency department (ED). The tool was designed to improve communication for all parents and to support shared decision-making (SDM) about whether to perform a lumbar puncture (LP) for infants 29 to 60 days of age. Methods: We conducted a multiphase development and testing process: 1) individual, semistructured interviews with parents and clinicians (pediatric and general emergency medicine [EM] physicians and pediatric EM nurses) to learn their preferences for a communication and SDM tool; 2) design of a “storyboard” of the tool with design impression testing; 3) development of a software application (i.e., app) prototype, called e-Care; and 4) usability testing of e-Care, using qualitative assessment and the system usability scale (SUS). Results: We interviewed 27 parents and 23 clinicians. Interviews revealed several themes, including that a communication tool should augment but not replace verbal communication; a Web-based format was preferred; and information about infections and testing, including the rationales for specific tests, would be valuable. We then developed separate versions of e-Care for infants ≤ 28 days and 29 to 60 days of age, in both English and Spanish. The e-Care app includes four sections: 1) homepage; 2) why testing is done; 3) what tests are done; and 4) what happens after testing, including a table for parents of infants 29 to 60 days of age to compare the risks/benefits of LP in preparation for an SDM conversation. Parents and clinicians reported that e-Care was understandable and helpful. The mean SUS score was 90.3 (95% confidence interval = 84 to 96.6), representing “excellent” usability. Conclusions: The e-Care app is a useable and understandable tool to support communication and SDM with parents of febrile infants ≤ 60 days of age in the ED.