Unable to start debugging on the web server. Unable to connect to the web server. Verify that the web server is running and that incoming HTTP requests are not blocked by a firewall.

Problem

When trying to debug  your solution or project, hosted on IIS Express, the following error occurs:

Unable to start debugging on the web server. Unable to connect to the
web server. Verify that the web server is running and that incoming
HTTP requests are not blocked by a firewall.

Solution

Change the project's Web settings to "IIS Express" instead of "External Host". This is under "Web" under the "Servers" section. Visual Studio should automatically fill in the Project Url.

Click the picture to enlarge.

Explanation

When a project's Web settings are set to an external server, Visual Studio will try to connect to that server to debug the project. This would be used if you were running IIS (not IIS Express) on your local machine and wanted Visual Studio to debug the app running on IIS.

Other things to try

• Restart Visual Studio, which also restarts IIS Express
• Run Visual Studio as Administrator.