Tamper a session by setting breakpoints that can be automatic (after/before every request or response) or custom ones – insert breakpoints only when certain conditions are met. You can also use the quick exec box to create simple breakpoints for whenever a certain URL is hit. Fiddler then pauses the processing of the session and permits manual alteration of the request and the response. You can also choose the response that will be automatically returned.
Traffic rewriting may also be performed automatically by script or extensions running inside Fiddler. This feature proves useful for security testing, as well as for general functionality testing, because all code paths can be exercised.