Thanks to the WebGL graphics API specification for the JavaScript programming language, the possibility of using the GPU capabilities in a web browser without the need for an ad-hoc plug-in is now coming true. This paper introduces SpiderGL, a JavaScript library for developing 3D graphics web applications. SpiderGL provides data structures and algorithms to ease the use of WebGL, to define and manipulate shapes, to import 3D models in various formats, to handle asynchronous data loading. We show the potential of this novel library with a number of demo applications. Furthermore, we introduce MeShade, a SpiderGL-based web application for shader material editing from within the web browser, which produces all the code needed for embedding interactive 3D model visualization capabilities inside web pages and online repositories.