Building web applications is hard work. There are so many things that can go wrong, so many technologies to learn, and so many issues that remain undiscovered because everything is designed to allow things to continue to work even when they’re not quite right. All of our fault tolerant design begins to work against us.
Most people remain unaware of precisely how their web application is interacting with the web browsers that their clients have installed. If analytics are present on the site then the number of requests ending in a 404 status (File not found) may be logged but identifying precisely why the client was requesting a page in the first place may be difficult or impossible.
This is where Fiddler, a free tool, can simplify the process substantially. Fiddler is a transparent proxy that automatically adds itself to the WININET chain so that it can see every request being made. It logs those requests and the responses to allow you to see what is working and what isn’t working.