Fiddler: Is It Possible To Replace Part Of Url Using Onbeforeresponse Function?

if (oSession.HostnameIs('www.youtube.com') && oSession.oResponse.headers.ExistsAndContains('Content-Type','text/html')){ oSession.utilDecodeResponse();

Solution 1:

You can replace anything in the url inside OnBeforeResponse, but doing so won't do anything useful, because the URL has already been sent to the server by then, so changing it that late has no visible impact to anything outside of Fiddler.

If you want to change the URL, do so inside OnBeforeRequest. In your FiddlerScript, look for the urlreplace handler to see how that works.