Mental health applications have shown promise in improving mental health and quality of life in a variety of contexts, such as depression, anxiety, and stress. However, multiple barriers to optimization of mental health application design exist, most prominently, the lack of research. In addition, adherence levels for mental health applications vary depending on the user’s mental health, motivation, and internal features of the application. Specifically, the relationship between mental health applications, adherence, and the reduction of depressive symptoms through different application features is an under-explored area of research. The primary purpose of the current study is to investigate the effect of customization on depressive symptoms, adherence, and motivation under customization and standard-no customization conditions. Furthermore, the secondary aim of the current study is to examine whether mobile journaling, mood tracking, and reminders, in addition to customization, also lead to a reduction of depressive symptoms and increased adherence and motivation rates. The current study also aims to investigate whether these four features lead to reduced levels of anxiety, stress, and rumination. Mental health symptoms, motivation, and identification will be measured using self-report questionnaires, while adherence will be collected from the completion rate of cognitive behavioral therapy (CBT) modules. A predicted total of 100 undergraduate students will complete a 14-day trial with the CBT mental health application, completing a total of seven modules. It is expected that the customization condition will result in reduced depressive, anxiety, stress, and rumination symptoms compared to the standard- no customization condition. Additionally, it is predicted that the customization condition will have a higher adherence rate, and motivation, and identification with the avatar compared to the standard-no customization condition. These findings could have potential implications for improving the optimization of mental health application design, such as imparting new research regarding adherence to further assist developers.