"We can't open this add-in from localhost" when loading an Office Add-in or using Fiddler
When you load an Office Add-in from https://localhost or when you use Fiddler, you receive the following error:
We can't open this add-in from localhost.
One cause of this error is that the Microsoft Edge Web Viewer does not have a loopback exemption. To resolve this issue, use either of these options to add a local loopback exemption to Desktop App Web Viewer:
Option 1: Use command to add a local loopback exemption
- Open a command prompt as administrator.
- Run the following command:
CheckNetIsolation LoopbackExempt -a -n="microsoft.win32webviewhost_cw5n1h2txyewy"
Option 2: Use Fiddler to add a local loopback exemption
- Select Tools > Win8 Loopback Exemptions.
- Add an exemption to Desktop App Web Viewer.
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