Debugging

There are many popular tools for web performance profiling/debugging these days. From my personal tool set I could mention Firebug, IE Developers Toolbar (integrated with IE from version > 8) or Fiddler. The common problem with those tools is that they are installed and run locally on developers machine. Sometimes, for example when behaviour of the web app depends on loading all elements in the specific order or time, it is important to determine if those factors vary in different geographical locations. The download speed for China and Germany could be very different. If you face with this kind of problems I could recommend you a great distributed web performance profiler - WebPageTest.

Have you ever had a problem with a user complaining on and on that when he clicks some button in your application his computer hangs but it works fine on any other machine where you have tested it? The web service is consuming all the available memory in completely indeterministic way? Or maybe your web application is magically crashing on production machine when it works in the same usage scenario on development and test environment? If not, you are probably in about 1% of the most luckiest developers in the world (or you are not the developer).