This registration covers only Aim 1b, which focuses on testing usability. The study will include 20 participants who are breast cancer patients. Participants will be observed using the tool on their mobile devices, and their experience will be evaluated using a "think-aloud" method to capture their thoughts and reactions. Interviews will include open-ended questions about the content and format of the decision aid, with follow-up prompts to gather feedback on design elements (length, order, graphics), comprehension, ease of use, acceptance, and engagement with the tool. Knowledge will be measured using the Decision Quality Instrument before and after using the tool. Results will be analyzed to develop recommendations for the final version of the tool.