Solution to "Port '443' is in use" When Starting a Web App from Visual Studio

If you see this error when trying to run a web app in Visual Studio – that means something is currently running on that port.

To find out what app is using that port…

Open resmon.exe

Go to Network tab, Listening Ports

Find 443 (or whatever port VS is complaining about)

And see what app is using it – and kill it.

In my case Skype was using 443.

Signing out of Skype solved the problem.