How to determine the URL a web project will run under (the start URL)?

Hi, my extension needs to know the URL that any web project/site in the solution will run under.  The port specifically.

I've researched some ways such as watching the IIS Express logs for new entries (hopefully there's a more direct way?), or looking at the project options (but this doesn't help with the port).

Ideally I'd like an event that occurs when the project is run and IVsWebBrowsingService.CreateWebBrowser is called from the IDE.

Any ideas how to accomplish this please?

Thanks