Abstract: We present Viser, a toolkit for 3D visualization in robotics and computer vision. Viser aims to bring easy and extensible 3D visualization to Python: we provide comprehensive 3D scene and 2D GUI primitives, which can be used independently with minimal setup or composed to build specialized interfaces. This paper details features and key design choices—an imperative-style API and a web-based viewer—which improve compatibility with modern programming patterns. We then discuss system architecture, adoption, and limitations.