How to Add Startup.cs in a .NET Core Project (manually)

In .NET 6 and later, Startup.cs is optional because configuration is done in Program.cs using Minimal Hosting Model. But if you want to use the traditional Startup.cs structure, you can manually add it.

Steps to Add Startup.cs:

1. Right-click your project → Add → New Item

2. Select Class, name it Startup.cs

1. Add the following code in Startup.cs

public class Startup
{
    public IConfiguration Configuration { get; }
    
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllers(); // Add MVC or API services
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.UseRouting();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }
}

    

2. Modify Program.cs to Use Startup

using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Hosting;

namespace YourAppNamespace
{
    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup &lt Startup &gt(); 
                });
    }
}