# Microsoft Extensions Configuration

Microsoft.Extensions.Options patterns including IValidateOptions, strongly-typed...

- Repository: https://github.com/Aaronontheweb/dotnet-skills (1244 stars)
- Category: Business
- License: MIT
- Last updated: 2026-10-28
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add Aaronontheweb/dotnet-skills --skill microsoft-extensions-configuration -g -a claude-code -y`
Codex: `npx skills add Aaronontheweb/dotnet-skills --skill microsoft-extensions-configuration -g -a codex -y`
Cursor: `npx skills add Aaronontheweb/dotnet-skills --skill microsoft-extensions-configuration -g -a cursor -y`
Gemini CLI: `npx skills add Aaronontheweb/dotnet-skills --skill microsoft-extensions-configuration -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add Aaronontheweb/dotnet-skills`

## Description

Microsoft.Extensions.Options patterns including IValidateOptions, strongly-typed settings, validation on startup, and the Options pattern for clean configuration management.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Microsoft.Extensions Configuration Patterns

## When to Use This Skill

Use this skill when:
- Binding configuration from appsettings.json to strongly-typed classes
- Validating configuration at application startup (fail fast)
- Implementing complex validation logic for settings
- Designing configuration classes that are testable and maintainable
- Understanding IOptions<T>, IOptionsSnapshot<T>, and IOptionsMonitor<T>

## Reference Files

- [advanced-patterns.md](advanced-patterns.md): Validators with dependencies, named options, complete production example (AkkaSettings), and testing validators

## Why Configuration Validation Matters

**The Problem:** Applications often fail at runtime due to misconfiguration - missing connection strings, invalid URLs, out-of-range values. These failures happen deep in business logic, far from where configuration is loaded.

**The Solution:** Validate configuration at startup. If invalid, fail immediately with a clear error message.

```csharp
// BAD: Fails at runtime when someone tries to use the service
public class EmailService
{
    public EmailService(IOptions<SmtpSettings> options)
    {
        var settings = options.Value;
        // Throws NullReferenceException 10 minutes into production
        _client = new SmtpClient(settings.Host, settings.Port);
    }
}

// GOOD: Fails at startup with clear error
// "SmtpSettings validation failed: Host is required"
```

---

## Pattern 1: Basic Options Binding

### Define a Settings Class

```csharp
public class SmtpSettings
{
    public const string SectionName = "Smtp";

    public string Host { get; set; } = string.Empty;
    public int Port { get; set; } = 587;
    public string? Username { get; set; }
    public string? Password { get; set; }
    public bool UseSsl { get; set; } = true;
}
```

### Bind from Configuration

```csharp
builder.Services.AddOptions<SmtpSettings>()
    .BindConfiguration(SmtpSettings.SectionName);

The rest: https://github.com/Aaronontheweb/dotnet-skills/blob/HEAD/skills/microsoft-extensions-configuration/SKILL.md