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Type-safe appsettings configuration in .NET Core

Configuration errors have a special way of ruining your day. You deploy to production, everything looks fine, then a specific code path hits and boom - NullReferenceException because appSettings["SomeKey"] returned null or you mistyped the configuration e.g. appSettings["Somkey"].

I've been burned by this enough times that I now default to strongly-typed configuration classes with required properties. This catches missing configuration at startup rather than runtime, and gives you IntelliSense when accessing values.

Setup #

Create a configuration class that mirrors your appsettings.json structure:

public class AppSettings
{
    public required ConnectionStringsConfig ConnectionStrings { get; init; }
    public required LoggingConfig Logging { get; init; }

    public class ConnectionStringsConfig
    {
        public required string DefaultConnection { get; init; }
    }

    public class LoggingConfig
    {
        public required string LogLevel { get; init; }
    }
}

Corresponding appsettings.json:

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=myserver;Database=mydb;"
  },
  "Logging": {
    "LogLevel": "Information"
  }
}

Register both IOptions<AppSettings> and the settings object directly:

builder.Services.Configure<AppSettings>(builder.Configuration);
builder.Services.AddSingleton(x => x.GetRequiredService<IOptions<AppSettings>>().Value);

The dual registration gives you clean injection in most cases, plus IOptions<T> when you need change notifications.

Usage #

Constructor injection:

public class MyService(AppSettings appSettings)
{
    public void DoWork()
    {
        var connectionString = appSettings.ConnectionStrings.DefaultConnection;
        // IntelliSense works, no magic strings, no null checks needed
    }
}

Blazor pages:

@inject AppSettings appSettings

Minimal APIs:

app.MapGet("/api/status", (AppSettings settings) => 
{
    var connectionString = settings.ConnectionStrings.DefaultConnection;
    return Results.Ok(new { Status = "Healthy" });
});

Why this works #

Required properties ensure missing configuration fails fast at startup with clear error messages. Nested classes as inner classes keep related settings grouped and make the hierarchy obvious. The compiler catches configuration problems immediately instead of NullReferenceExceptions deep in production code paths. IntelliSense is available, so no typos in magic strings.