Abstract: We describe Tracy, an offline graphics debugging and system analysis toolkit for cross-platform system and application development in mobile graphics. Tracy operates by recording graphics function calls and argument data of unmodified applications into a trace file for offline playback, debugging, and performance analysis. In addition, traces can be edited and converted into platform-independent C files. We pay special attention to real-time performance; our trace compression mechanism allows interactive use of applications even when tracing long, multi-thousand-frame traces in real mobile hardware. We describe the use of the toolkit through real-world use cases such as debugging a visual error or a performance problem in an application, analyzing the application quality, and benchmarking a graphics engine.