While using Fiddler to examine HTTP traffic on your localhost, you may get this error:
Fiddler: No connection could be made because the target machine actively refused it
This happens because by default .NET bypasses local proxies while sending requests and Fiddler runs as a proxy. One way to catch local HTTP traffic is to change the URL in the browser by appending a "dot" to it (after the localhost), for example:
If this still does not work, then make sure that Fiddler is set to ignore IPv6 because VS.NET in-built web-server by default uses IPv4 stack.