Can't See Localhost from Uwp App

Loopback enabled UWP app successfully reach localhost service only when Fiddler is running

Fiddler is able to Allow your App to use the local network loopback.

Simply check your App and you can reach your WebService.
You will see if you uncheck your App, you won't reach your WebService again.

Visual Studio enables the local network loopback while debugging as well if you check the option in your Projects Debugging Properties. (Project -> Properties -> Debugging -> Allow local network loopback)

UWP Enable local network loopback

For a line of business app use the checknetisolation.exe tool to grant the app a loopback exception.

To enable loopback use this command:

c:\>checknetisolation loopbackexempt -a -n=<package family name>

To disable loopback use this command:

c:\>checknetisolation loopbackexempt -d -n=<package family name>

The package family name for a UWP app can be found in several places: Visual Studio shows it in Package.appxmanifest editor on the packaging tab, PowerShell's get-appxpackage cmdlet displays it, etc. It will look something like "MyPackage_edj12ye0wwgwa"

In some cases loopback exemption will work for some time and then stop working. In this case you might need to run the following command to clean/remove all exemptions and then add them back one by one to get back in a good state. (from Pawel Sledzikowski's comment)

c:\>checknetisolation loopbackexempt -c

There is a whitepaper with more details at https://msdn.microsoft.com/en-us/library/windows/apps/dn640582.aspx

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