Optional appsettings.local.json in (new format) visual studio project

For .NET 6, you can use this.

Also make sure, you git ignore appsettings.local.json to avoid check-in sensitive information like password and secrets.

var builder = WebApplication.CreateBuilder(args);

// Add configurations
builder.Host.ConfigureAppConfiguration((hostingContext, config) =>
{
    config.Sources.Clear();

    var env = hostingContext.HostingEnvironment;

    config.SetBasePath(env.ContentRootPath)
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true) //load base settings
            .AddJsonFile("appsettings.local.json", optional: true, reloadOnChange: true) //load local settings
            .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true) //load environment settings
            .AddEnvironmentVariables();

    if (args != null)
    {
        config.AddCommandLine(args);
    }
});

For .Net Core >2.1 you can simply chain the extension method ConfigureAppConfiguration(Action<WebHostBuilderContext, IConfigurationBuilder> configureDelegate) to your WebHost. Here is an example:

WebHost.CreateDefaultBuilder(args)
    .ConfigureAppConfiguration((hostingContext, config) =>
    {
        config.AddJsonFile(
            "appsettings.Local.json",
             optional: true,
             reloadOnChange: true);
    })
    // ...

And of course ignore the appsettings.Local.json in your .gitignore.

With v2 this is dead simple.

1. Add an appsettings.local.json to your project (it should nest itself below the main appsettings.json file).
2. Add appsettings.local.json to your .gitignore

3. In your startup.cs within the constructor do the following:

   public class Startup
   {
       public IConfigurationRoot Configuration { get; }
   
       public Startup(IHostingEnvironment env)
       {
           var builder = new ConfigurationBuilder()
               .SetBasePath(env.ContentRootPath)
               .AddJsonFile("appsettings.json", optional: false, reloadOnChange: true) //load base settings
               .AddJsonFile("appsettings.local.json", optional: true, reloadOnChange: true) //load local settings
               .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true) //load environment settings
               .AddEnvironmentVariables();
   
           Configuration = builder.Build();
       }
   
       /*
        * rest of your startup.cs
        */
   }