There has been an increase in online debate platforms in recent years that allow individuals to exchange their opinions or to foster civic engagement. Even though the design of platforms has a significant influence on the quality of debates, research has yet to systematically analyze the graphical user interfaces of debate tools that are currently in use. To address this, we collected 25 off-the-shelf online debate platforms and conducted a comparative visual analysis of their graphical user interfaces. We identified different types of platforms, interface blocks, hierarchies, and display layout patterns. We found a strong similarity among these platforms in their design and a shared emphasis on individual input. Drawing from these insights, we discuss how the design of platforms frames the practice of debate and identify potential design dimensions in order to move beyond the existing boundaries of online debate.