I just wanted to check if my HTTP caching for my website is working especially since I moved to a CDN.
Now I used both Fiddler and Firebug and what I am seeing is that requests for ALL scripts and images on my page every time I navigate to it. Response code is 200.
If I open the page in Chrome, the developer tools also show me all these requests but Chrome also tells me that the requests are served from the Cache. Chrome requests are not listed in Fiddler (while FF and IE requests are).
My original assumption was that if Firefox or Internet Explorer get a file from their cache that request wouldn't show up at all in Fiddler.
I checked my caching headers and since Chrome behaved exactly like I expected I am asking myself if my assumption about Fiddler was wrong. Are FF/IE behaving differently when Fiddler is started? Is Fiddler showing cache hits?
As a network proxy, Fiddler is not able to show anything that comes out of the cache. If you see a request in Fiddler, then that request was sent over the wire.
One thing to keep in mind is that if you're refreshing the page (e.g. with the button or F5) then the cache can be bypassed; see http://blogs.msdn.com/b/ieinternals/archive/2010/07/08/technical-information-about-conditional-http-requests-and-the-refresh-button.aspx
来源：https://stackoverflow.com/questions/5851265/fiddler-showing-cache-hits