This work describes RoboViz, a new software program designed to assess and develop agent behaviors in a multi-agent system, the RoboCup Soccer Simulation 3D sub-league. RoboViz is an interactive monitor that renders both agent and world state information in a three-dimensional scene. In addition, RoboViz provides programmable remote drawing functionality to agents or other clients that can communicate over a network. The tool facilitates real-time visualization of agents running concurrently on the SimSpark simulator to provide higher-level analysis of agent behaviors not currently possible with existing tools. Provided appropriate hardware, the monitor and debugging tool can produce high-quality stereo vision images. RoboViz is proposed as a replacement for the current SimSpark 3D league monitor to benefit developers as well as elevate public interest in the 3D simulation league, and it has been used officially at the 2011 German Open in Magdeburg, Germany. RoboViz was released in February 2011 as an open-source project under the Apache 2.0 license.