Fiddler: Error 502 Proxy Error


I am using Fiddler to debug all HTTP request of my ASP.NET application.

For a while (about 6 months) I had no problem. All HTTP requests appeared on Fiddler and so on.

The last two days Fiddler stoped working :/ Always returns the same error: "The request failed with HTTP status 502: Proxy Error ( The ISA Server denied the specified Uniform Resource Locator (URL). )."

The strange thing is that only happens to my application, i. e. all HTTP requests from youtube, email, etc, appear on Fiddler.

What is the problem here?


From my case adding this line on OnBeforeRequest function in Fiddler Script fixed it for me,

oSession["x-OverrideSslProtocols"] = " ssl3;tls1.0;tls1.1;tls1.2";


I had the same issue with Fiddler - my HTTPS site worked fine in IE, however got <strong>502</strong> error in <strong>Chrome</strong>. After analyzing the issue, I found that has manual proxy enabled in Fiddler (not recommended):

Tools -> Fiddler Options -> Gateaway

it was the root cause of this strange behavior. Switching to "System Proxy" made this working for both IE and Chrome.


I had a scenario where production url was https and test was http.

When wrongly calling test with https in fiddler then I got 502 and ended here on stack overflow.

I will just leave this here in case anyone else does the same mistake.


I solved my problem =)

I seems that something changed at my company network. So I changed the file CustomRules.js from Fiddler and added some lines at OnBeforeRequest.

Now, everything works just fine

Best regards.


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