Microsoft Extensions Configuration

If you're tired of runtime configuration failures in .NET apps, this walks you through the Options pattern with startup validation. It covers IOptions vs IOptionsSnapshot vs IOptionsMonitor, when to use Data Annotations versus IValidateOptions for complex cross-property rules, and how ValidateOnStart makes misconfiguration fail immediately instead of deep in production. The examples are practical, from basic appsettings.json binding to background services that react to config changes. The anti-patterns section alone is worth it, especially the reminder to never inject IConfiguration directly when you could have strongly-typed, validated settings classes instead.