Abstract: The Flipped Classroom approach with large classes, especially at higher education level, is known to pose serious challenges to effective students’ participation. One of these challenges is the adequacy of the teachers’ preparation in order to meet all / most of the possible concerns/questions by the students. Since contact hours are limited, the risk is to use all the time to answer only few concerns by those students who dare to speak up. In this brief paper, we present a Video-tagging Tool to support the Flipped Classroom approach. The approach is akin to Students’ Response System, but the novelty is that it is asynchronous. The tool allows students to tag an educational video they are supposed to watch before the class, expressing their opinion on what is not clear or particularly clear as well as asking time-stamped questions. A dashboard allows the teacher to monitor her/his students’ feedback in real time and see aggregated data about the points that most find unclear (therefore, to be tackled in presence) or so clear that no additional explanation is needed, as well as questions/comments. The tool was made available for free in March 2020 and has gathered thousands of users from all around the globe.