  This paper introduces RL Brush, a level-editing tool for tile-based games
designed for mixed-initiative co-creation. The tool uses
reinforcement-learning-based models to augment manual human level-design
through the addition of AI-generated suggestions. Here, we apply RL Brush to
designing levels for the classic puzzle game Sokoban. We put the tool online
and tested it in 39 different sessions. The results show that users using the
AI suggestions stay around longer and their created levels on average are more
playable and more complex than without.
