This study evaluated the effectiveness of the Crosswords: Learn English Words application in enhancing the English vocabulary mastery of 7th-grade students at SMP N 1 Kedungbanteng. The research was motivated by observed difficulties in student vocabulary acquisition and the necessity for innovative, interactive digital instructional media. The methodology employed a quasi-experimental pre test/post-test non-equivalent control group design. Two classes, designated as the experimental group (VII B) and the control group (VII F), were selected through cluster random sampling with lottery, each consisting of 32 students. Data were gathered using pre-test and post-test instruments. The resultant data were analyzed using the Mann-Whitney test (non-parametric hypothesis testing) to assess significant differences in vocabulary improvement, which was measured by N-gain scores. The findings indicate a statistically significant difference and a substantial improvement in vocabulary mastery in the experimental group following the intervention. Based on the Mann-Whitney test, the Asymp (Sig) value was 0.013, which means that the hypothesis (ha) was accepted. Specifically, the mean scores in the experimental class increased markedly from 72.1 (pre-test) to 88.4 (post-test), yielding an average N-gain score of 65%. In contrast, the control group exhibited a lower increase, with mean scores rising from 74.1 to 80.3, corresponding to an average N-gain score of only 32%. Based on the N-gain classification, the effectiveness of the Crosswords: Learn English Words application in the experimental class is categorized at the "Quite Effective" level.