The enormous flexibility of the modern GPU rendering pipeline as well as the availability of high-level shader languages have led to an increased demand for sophisticated programming tools. As the application domain for GPU-based algorithms extends beyond traditional computer graphics, shader programs become more and more complex. The turn-around time for debugging, profiling, and optimizing GPU-based algorithms is now a critical factor in application development which is not addressed adequately by the tools available. In this paper we present a generic, minimal intrusive, and application-transparent solution for debugging OpenGL Shading