This research proposes the development of a web-based assessment system to identify students' misconception. The system, named WAS (web-based assessment system), can identify students' misconception profile on linear kinematics automatically after the student has finished the test. The test instrument was developed and validated. Items were constructed and arranged from the result of a focus group discussion (FGD), related to previous research. Fifty-eight students (female = 37, male = 21) were used as samples. They were from different classes with 18 students from the gifted class and another 40 students from the normal class. WAS was designed specifically to support the teacher as an efficient replacement for a paper-based test system. In addition, WAS offers flexible timing functionally, stand-alone subject module, robustness and scalability. The entire WAS program and interface was developed with open source-based technologies such as the XAMP server, MySQL database, Javascript and PHP. It provides results immediately and provides diagrammatic questions as well as scientific symbols. It is feasible to apply this system to many students at once. Thus, it could be integrated in many schools as part of physics courses.