RealtimeCSG is a real-time constructive solid geometry (CSG) level design tool for Unity. It operates exclusively as an Editor extension, providing non-destructive boolean operations on brushes (box, sphere, cylinder, stairs, free-draw) with immediate visual feedback in the Scene view. The architecture is manager-driven: `InternalCSGModelManager` orchestrates hierarchy updates, mesh generation, and caching, while a native C++ DLL handles performance-critical CSG calculations. The tool offers multiple edit modes (Generate, Edit, Clip, Place, Surface) each with custom scene tools, handles, and inspector GUIs. It supports material assignment, UV editing, export to FBX or Unity prefab, and includes a full half-edge mesh representation (`ControlMesh`) for local mesh editing (vertex/edge/polygon). The codebase heavily relies on Unity Editor APIs, reflection to access internal Unity systems, and conditionals for cross-version compatibility. It is a production-grade, feature-rich tool used in game development workflows, though the closed-source native core and editor-only architecture limit runtime usage and cross-platform deployment.