This thesis, the interactive of formative assessment through gamification tool of ‘Kahoot!’ in learning English at reading classes of second grade of SMA N 5 Semarang, has a purpose to describe the process of it, including the implementation of ‘Kahoot!’ and students’ learning activeness when assessed using ‘Kahoot!’. This study used the descriptive qualitative method because the data were analyzed using sentences. The data were collected by three-technique; observation, interview, and documentation. Process of data analysis involved three activities; those are data reduction, data display, and conclusion drawing or verification. Descriptive qualitative analysis was used to present the result of the study in the form of descriptive explanation. These descriptions were analyzed based on the principles of the assessment process used a digital tool. The result of this study showed that ‘Kahoot!’ is utilized for a post-test in learning English. The assessment process using ‘Kahoot!’ is more convenient and comfortable than the use of paper-based testing. But, the preparation of doing the assessment using ‘Kahoot!’ takes a long time. The use of ‘Kahoot!’ is quite effective because it can’t accommodate the assessment based-text. Furthermore, the students enjoy and are motivated when assessed using ‘Kahoot!’. They must compete with their friends to become a winner. The process of assessment involved teacher-students and students-students interaction that creates an interactive formative assessment.