Reliable numerical computations are central to HPC and ML. We present FlowFPX, a Julia-based tool for tracking the onset and flow of IEEE Floating-Point exceptions that signal numerical defects. FlowFPX’s design exploits Julia’s operator overloading to trace exception flows and even inject exceptions to accelerate testing. We present intuitive visualizations of summarized exception flows including how they are generated, propagated and killed, thus helping with debugging and repair.