Access environment name in Program.Main in ASP.NET Core

I think the easiest solution is to read the value from the ASPNETCORE_ENVIRONMENT environment variable and compare it with Environments.Development:

var environment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
var isDevelopment = environment == Environments.Development;

.NET 6 or higher

Starting from .NET 6 using the new application bootstrapping model you can access the environment from the application builder:

var builder = WebApplication.CreateBuilder(args);
var isDevelopment = builder.Environment.IsDevelopment();