Fiddler is a web debugging tool that captures HTTP traffic between chosen computers and the Internet. It allows you to analyze incoming and outgoing data to monitor and modify requests and responses before they hit the browser.
Fiddler gives you extremely detailed information about HTTP traffic and can be used for testing the performance of your websites or security testing of your web applications (e.g. Fiddler can decrypt HTTPS traffic).When you launch Fiddler, HTTP traffic will start to be captured automatically.
To toggle traffic capturing, hit F12. You can choose which processes you wish to capture HTTP traffic for by clicking on “All Processes” in the bottom status bar, or by dragging the “Any Process” icon from the top menu bar onto an open application.