Technology and artificial intelligence (AI) advancements are increasingly impacting second language (L2) learning, particularly in writing skills development. Motivated students seeking writing feedback can benefit from AI implementation, with writing feedback literacy being crucial for effective use. Engaged students with specific writing goals benefit from ongoing practice and learning to attain high-quality outcomes, whether from formal or informal settings such as AI application. AI's integration into L2 education underscores the need to comprehend its role in improving L2 writing engagement, writing feedback literacy, and writing outcome. A mixed-method study was conducted, which involved 46 students at the upper-intermediate level. The student cohort was divided into two groups for the purpose of the study. One group was designated the control group, while the other was the experimental group, each comprising 23 students. By using Wordtune, an AI-based application, the experimental group was able to significantly improve their writing outcomes, engagement, and feedback literacy when compared to the control group. Furthermore, the Wordtune application received positive feedback from students interviewed about its ability to improve their writing outcomes, engagement, and feedback literacy. These findings will contribute to our understanding of AI in L2 learning and inform instructional considerations for Wordtune's application.