Fiddler Ideas

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Do not warn on certificate mismatch when using localhost.fiddler for localhost

In order to debug a website served on localhost by IIS Express you need to use localhost.fiddler to get traffic to show up in Fiddler, but if you use HTTPS you'll first get a warning that the certificate name does not match and you have to manually confirm this connection.

This is generally a good idea, but in the case of localhost and localhost.fiddler I think this warning should not be shown, as having to use localhost.fiddler is simply a technical restriction that Fiddler should know about...

  • Guest
  • Oct 3 2018
  • Under review
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  • Eric Lawrence commented
    5 Oct, 2018 12:54pm

    This is a good bug to fix.


    The workaround for now is simple. Click Rules > Customize Rules. Scroll to OnBeforeRequest and add the code:

     if (oSession.HostnameIs("localhost")) {
    // Use X-IgnoreCertErrors if you want to ignore *ALL*
    // errors (e.g. untrusted root)
    oSession["X-IgnoreCertCNMismatch"] = "ImplicitlyTrustingLocalServerCN";