BrickBench: Evaluating Agentic Brick Design

We propose BrickBench, a benchmark for agentic text-conditioned LEGO-set design. Given a prompt, an agent is tasked with producing an assembly that not only satisfies semantic and design criteria, but that also can be physically built. To do so, it must select parts from a discrete library and reason jointly about local and global constraints. We provide BrickAgent, an environment in which coding agents build, and we score validity, alignment, and design across three settings that vary scale and part availability. We find that leading agents largely satisfy the verifiable physical and semantic specifications, but fall substantially short of human design quality.