XDT Transformation to add custom error page URLs to an ASP.NET application.

gistfile1.xml

  <system.webServer>
    <httpErrors errorMode="Custom" existingResponse="Replace" xdt:Transform="Insert">
      <remove statusCode="404" />
      <error statusCode="404" path="/error/404" responseMode="ExecuteURL" />
      <remove statusCode="500" />
      <error statusCode="500" path="/error/500" responseMode="ExecuteURL" />
      <remove statusCode="403" />
      <error statusCode="403" path="/error/403" responseMode="ExecuteURL" />
    </httpErrors>
  </system.webServer>