Add this to the section in your web.config
<defaultProxy> <proxy proxyaddress="" /> </defaultProxy> is the default address that Charles/Fiddler uses.

If you are doing requests against a site that uses HTTPS you can get some certificate errors like this one:
The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.

Just add this line of code right before you are executing your WebClient requests
ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => true;

You could also add the following to your web.config

<configuration> <> <settings> <servicePointManager checkCertificateName="false" checkCertificateRevocationList="false" /> </settings> </> </configuration>