Environment tag dosent work?

If you use .NET CORE 1.0, namespace changes to

"Microsoft.AspNetCore.Mvc.TagHelpers"

It seems you need to add @addTagHelper "*, Microsoft.AspNetCore.Mvc.TagHelpers" to the file containing the html, or if you follow the setup of a default project add it to _ViewImports.cshtml.

Also make sure you have added Microsoft.AspNetCore.Mvc.TagHelpers to your project.json.

I had this issue because I wasn't using app.UseStaticFiles(); in my startup