How to check if I am using localhost server or not in C# MVC?

You can simply use the below code to check if you are on localhost

if(HttpContext.Current.Request.IsLocal )
{
   //Yes you are on localhost website
}

OR

//check using AbsoluteURI
var IsLocal = HttpContext.Current.Request.Url.AbsoluteUri.
            StartsWith("http://localhost:");

I have tested the first solution which is more simpler but second one should also work where we are checking is Absolute URI starts with "localhost".

Above works if you are using ASP.NET MVC, but if you are using ASP.NET Core 2.1 , you can check if it is local using below code

var callingUrl = Request.Headers["Referer"].ToString();
var isLocal = Url.IsLocalUrl(callingUrl); // return if URL is local

https://docs.microsoft.com/en-us/dotnet/api/Microsoft.AspNetCore.Mvc.IUrlHelper.islocalurl?view=aspnetcore-5.0#Microsoft_AspNetCore_Mvc_IUrlHelper_IsLocalUrl_System_String_

OR

If you are using ASP.NET Core 3.1, you can also try the below code

if (Request.Host.Host == "localhost") {
      // do something with local URL
}