What is the use of the Program.cs and Startup.cs files in ASP.NET Core?

Question

Anubhav Kumar · Answer

In ASP.NET Core, the Program.cs and Startup.cs files play a crucial role in
configuring and bootstrapping your application. Here's a clear explanation of their purposes:
Program.cs – Application Entry Point
Purpose:
Defines the main entry point of the application.Responsible for creating and running the web host (the environment in which the app runs).
Responsibilities:
Configures the host (web server, logging, etc.)Calls the Startup class to set up services and middleware.
Example (.NET Core 3.1 style):
public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }
    public static IHostBuilder CreateHostBuilder(string[] args) =andgt;
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =andgt;
            {
                webBuilder.UseStartupandlt;Startupandgt;();
            });
}
Startup.cs – App Configuration
Purpose:
Contains methods to configure services and the HTTP request pipeline.
Key Methods:
ConfigureServices(IServiceCollection services) Register app services, e.g., MVC, EF Core, authentication, etc.Configure(IApplicationBuilder app, IWebHostEnvironment env) Set up the
middleware pipeline (e.g., routing, error handling, static files).
Example:
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllersWithViews();
    }
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
            app.UseDeveloperExceptionPage();
        app.UseStaticFiles();
        app.UseRouting();
        app.UseEndpoints(endpoints =andgt;
        {
            endpoints.MapDefaultControllerRoute();
        });
    }
}
In .NET 6/7+, Program.cs Merges Everything
In .NET 6 and newer, Startup.cs is optional. The
Program.cs file uses a minimal hosting model, combining everything in one place:
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllersWithViews();
var app = builder.Build();
app.UseStaticFiles();
app.UseRouting();
app.MapDefaultControllerRoute();
app.Run();
Summary
File
Purpose
Used In
Program.cs
Entry point, host setup
All ASP.NET Core apps
Startup.cs
Configure services and middleware
.NET Core 2.x – 5.x (optional in .NET 6+)
Program.cs (Minimal API style)
Combines both responsibilities
.NET 6 and newer

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What is the use of the Program.cs and Startup.cs files in ASP.NET Core?

Anubhav Kumar

Can you answer this question?

1 Answers

`Program.cs` – Application Entry Point

Purpose:

Responsibilities:

Example (`.NET Core 3.1` style):

`Startup.cs` – App Configuration

Purpose:

Key Methods:

Example:

In .NET 6/7+, `Program.cs` Merges Everything

Summary

Liked By

File	Purpose	Used In
`Program.cs`	Entry point, host setup	All ASP.NET Core apps
`Startup.cs`	Configure services and middleware	.NET Core 2.x – 5.x (optional in .NET 6+)
`Program.cs` (Minimal API style)	Combines both responsibilities	.NET 6 and newer