This paper treats a 3D graphics software development system called IntelligentBox and its aspects as a rapid construction system for web 3D educational contents. IntelligentBox provides various 3D software components called boxes each of which has a unique functionality and a 3D visible shape. IntelligentBox also provides a dynamic data linkage mechanism that allows users to develop interactive 3D graphics applications only by combining already existing boxes through direct manipulations on a computer screen. However, developed 3D contents could not be available on the web. So, the author extended IntelligentBox system to make it possible to develop web 3D contents including web 3D educational contents. This paper introduces the web version of IntelligentBox and shows its availability as a development system for web and mobile 3D educational contents.