 This paper presents a new tool called the mobile app rating scale, MARS, which is designed to evaluate the quality of mobile health applications. The MARS consists of 23 items covering five different dimensions, engagement, functionality, aesthetics, information quality, and user experience. The authors conducted a pilot study with 50 mobile health apps and found that the MARS had excellent internal consistency and inter-rater reliability. This suggests that the MARS could be used as a reliable and valid tool for evaluating the quality of mobile health apps. This article was authored by Stoyanov, Stoyanar, Heids, Lian, Kavanaugh, David J, and others.