Options Dialog Box, Projects and Solutions, Web Projects
Applies to: 
Visual Studio 
Visual Studio for Mac
Note
This article applies to Visual Studio 2017. If you're looking for the latest Visual Studio documentation, see Visual Studio documentation. We recommend upgrading to the latest version of Visual Studio. Download it here
Sets the web server that web projects will use for development within Visual Studio. To access these options, select Tools > Options expand Projects and Solutions, and select Web Projects.
By default, running a web project in Visual Studio uses the Visual Studio Development Server. For more information, see Web Servers in Visual Studio for ASP.NET Web Projects.
Settings
Use the 64-bit version of IIS Express for web sites and projects
Select this option to use IIS Express instead of the Visual Studio Development Server. For more information, see Introducing IIS Express and IIS Express Overview.
Warn before running web applications when there are errors in the error list
If this option is set, you will be warned if you try to run your web application when it does not compile without errors.