From Ingenieurbuero David Fischer:
Proxy Sniffer is a professional, Web load and stress testing tool with an intuitive user-friendly interface. It permits you to analyze the performance characteristics and the stability of your Web server under various load conditions and to tune Web applications. The built-in Websurfing session recorder enables capturing all data between any Web browser and the Web application server(s). This allows a detailed analysis of all exchanged data that can be used to tune the content and the size of the Web pages.
Thereafter an exact copy of a recorded Websurfing session can be transformed automatically into a Java load test program which can be easily compiled and executed by using the GUI interface. All measured performance data and all occurred errors during a load test-run are stored inside a single result file, from which consolidated detailed statistics and diagrams can be created.