In performance analysis of computer systems, trace-driven simulation techniques have the important advantage of credibility and accuracy. Unfortunately, traces are usually difficult to obtain, and little work has been done to provide efficient tools to help in the process of reducing and manipulating them. In this paper, we present a tool we have developed to help in the data reduction and data analysis phases of trace-driven simulation studies. Our tool has three main advantages: it accepts a variety of common trace formats; it provides a programmable user interface in which many actions can be directly specified; and it is easy to extend. This tool is particularly helpful for reducing and analyzing complex trace data, such as traces of file system or database activity. In this paper, we present our design principles, our implementation techniques, and a few concrete examples of the use of this tool.