Pattern mining algorithms allow to extract structures from data to highlight interesting and useful knowledge. However, those approaches can only be truly helpful if the users can actually understand their outputs. Thus, visualization techniques play a great role in pattern mining, bridging the gap between the algorithms and the users. In this demo paper we propose GraphMDL Visualizer, a tool for the interactive visualization of the graph patterns extracted with GraphMDL, a graph mining approach based on the MDL principle. GraphMDL Visualizer is structured according to the behavior and needs of users when they analyze GraphMDL results. The tool has dierent views, ranging from more general (distribution of pattern characteristics), to more specic (visualization of specic patterns). It is also highly interactive, allowing the users to customize the dierent views, and navigate between them, through simple mouse clicks. GraphMDL Visualizer is freely available online.