About 1 in 8 women are diagnosed with breast cancer during their lifetime; among them over 80% have hormone receptor-positive (HR+) tumors. Long-term aromatase inhibitors are commonly prescribed to women with HR+ breast cancer after surgery, chemotherapy, and/or radiation to lower cancer recurrence rates and improve survival. Despite the potential improvement in survival outcomes, recent evidence suggests that aromatase inhibitor adherence and persistence rates are low. Multiple studies point to adverse side effects of adjuvant therapies as a key reason for lower adherence or premature discontinuation. Patients who do not take the full amount of their medication as prescribed or who discontinue their aromatase inhibitor treatment early do not receive the full intended treatment benefits, and consequently are at increased risk for all-cause mortality, cancer death, and recurrence. Monitoring of adverse effects and symptoms, especially between clinic visits, could help healthcare providers better manage symptoms and increase long-term treatment adherence. Evidence indicates that patients generally experience most adverse effects early in their treatment, typically within the first six months. We plan to enroll 20 subjects per study arm, for a total of 40 participants. Potential subjects for recruitment will be identified from the electronic health records system of the West Cancer Center. Physicians and nurses at the West Cancer Center refer potentially eligible patients to the study nurse coordinator. The nurse will review eligibility criteria with patients and provide an overview of the research study and seek informed consent. Patients who provide informed consent will immediately be asked to complete a brief baseline survey about their preferences for receiving prompts, either via email or via cell phone using a text message. After survey administration, all patients will be registered in the mobile health app, which will be used report medication adherence and any related adverse symptoms. Study participants will be randomized into one of two arms: 1) active prompts to use the study app or 2) use of study app, but no prompts. All participants will be followed for a minimum of 6-8 weeks (depending on their scheduled follow-up visits at the center) and will be asked to complete a follow-up survey during or shortly after their scheduled in-clinic appointment at the end of the study. Baseline and follow-up questionnaires will collect data on quality of life (FACT-ES), health literacy, and demographics. The web-based app will be used to ask patients about medication adherence in the previous 7 days, any new symptoms, or changes in the severity of symptoms.