In recent years, the widespread growth of mobile-assisted language learning using apps has made English vocabulary learning increasingly accessible. This study investigated students' perceptions of a vocabulary learning app developed by the researcher as a tool to help them to improve their L2 receptive vocabulary. The app, containing 20 levels, works with both iOS and Android. The participants were 14 undergraduate students at an English-medium university in Hong Kong. A qualitative methodology of semi-structured interviews captured a holistic overview and revealed students' perceptions of the app. The results suggested that Hong Kong university students have a strong motivation for acquiring an L2 vocabulary. Participants also indicated a preference for mobile applications using gamified features. The study highlights directions for future research into apps for English language learning.