Educational technology plays a major role in today’s learning as it offers significant advantages in delivering learning content, classroom communications, and assessing learners. Assessment is a cornerstone in modern and formal education and is particularly necessary for tracking progress, measuring knowledge or achievement, and planning future educational steps. This study investigates the effects of using an online game-based learning (GBL) approach in students’ assessment in terms of their performance and self-efficacy in English as a foreign language (EFL) learning. A quasi-experiment was conducted on intermediate school-level students, who were divided into two groups, namely control and experimental. Each group underwent an English language test conducted through a Google Form and a role-playing game developed to mimic the functionality of an assessment tool. The results indicate that the performance of the experiment group was neither affected positively nor negatively using the GBL assessment tool. On the other hand, the results also show that using such a tool has positively affected students’ self-efficacy levels.