In this paper, we introduce a visual debugger that helps us develop soccer agents for RoboCup Soccer 3D Simulation. The visual debugger enables us to monitor the internal state of a soccer agent and the soccer field graphically. We show the characteristic features of the debugger such as visualization of body position, field status, and game status. We also show a soccer agent that can be manually controlled by a game-pad. The communication protocol that is necessary for using the visual debugger is explained.