The Configuration Binding Source Generator in .NET 8

Configuration binding in .NET has always relied on reflection. When you call builder.Services.Configure<MyOptions>(config.GetSection("MySection")), the framework uses reflection to discover properties, match them to configuration keys, and set values. This works fine in standard deployments but becomes a problem with Native AOT, where the trimmer can remove the very metadata that reflection depends on.

.NET 8 introduced a configuration binding source generator that replaces this reflection with compile-time code generation.

Enabling the source generator

The generator is opt-in. Add a single property to your project file:

MyApp.csproj 
<PropertyGroup>
    <EnableConfigurationBindingGenerator>true</EnableConfigurationBindingGenerator>
</PropertyGroup>

That's it. The source generator intercepts calls to Bind, Get, and Configure extension methods and replaces them with generated binding code at compile time. Your application code doesn't change at all.

What gets generated

Given this options class:

Example.cs 
public class DatabaseSettings
{
    public string ConnectionString { get; set; } = "";
    public int MaxRetryCount { get; set; } = 3;
    public TimeSpan CommandTimeout { get; set; } = TimeSpan.FromSeconds(30);
}

And this registration:

Program.cs 
builder.Services.Configure<DatabaseSettings>(
    builder.Configuration.GetSection("Database"));

The source generator produces a binding method that explicitly reads each property from the configuration:

Example.cs 
// Simplified representation of what the generator produces
public static void BindDatabaseSettings(
    IConfiguration configuration, DatabaseSettings instance)
{
    if (configuration["ConnectionString"] is string connectionString)
        instance.ConnectionString = connectionString;

    if (configuration["MaxRetryCount"] is string maxRetryCount
        && int.TryParse(maxRetryCount, out var maxRetryCountValue))
        instance.MaxRetryCount = maxRetryCountValue;

    // ... and so on for each property
}

No reflection, no PropertyInfo enumeration, no runtime type inspection. The generated code is visible in your IDE under the analysers node if you want to inspect it.

Supported binding patterns

The generator handles the common binding methods:

Example.cs 
// All of these are intercepted by the source generator

// Options pattern registration
builder.Services.Configure<DatabaseSettings>(config.GetSection("Database"));

// Direct binding
var settings = new DatabaseSettings();
config.GetSection("Database").Bind(settings);

// Get with type parameter
var settings = config.GetSection("Database").Get<DatabaseSettings>();

It also supports nested objects, collections, and dictionaries:

Example.cs 
public class AppSettings
{
    public DatabaseSettings Database { get; set; } = new();
    public List<string> AllowedOrigins { get; set; } = [];
    public Dictionary<string, FeatureFlag> Features { get; set; } = new();
}

public class FeatureFlag
{
    public bool Enabled { get; set; }
    public double Percentage { get; set; } = 100;
}
data.json 
{
  "Database": {
    "ConnectionString": "Server=localhost;Database=myapp"
  },
  "AllowedOrigins": ["https://example.com", "https://app.example.com"],
  "Features": {
    "DarkMode": { "Enabled": true, "Percentage": 50 },
    "NewCheckout": { "Enabled": false }
  }
}

Compile-time diagnostics

One benefit of the source generator approach is earlier error detection. If the generator encounters a type it can't bind — for example, a property with no public setter and no matching constructor parameter — it emits a compiler warning rather than silently failing at runtime.

Common warnings include:

These warnings help catch configuration binding issues during development rather than in production.

Performance impact

The practical performance difference for most applications is small — configuration binding typically happens once at startup. The real benefit is for applications using Native AOT or aggressive trimming, where reflection-based binding simply doesn't work.

However, if you're binding configuration in a hot path (which is unusual but does happen with IOptionsMonitor<T> and frequent configuration changes), the generated code avoids the overhead of repeated reflection.

Benchmarks from the .NET team show the generated binding is approximately 2-3x faster than reflection-based binding for small to medium options classes, with the gap widening for types with many properties.

Limitations

The source generator has a few constraints to be aware of:

Init-only properties are not supported in .NET 8 but are supported from .NET 9 onwards.

Constructor binding works but requires the constructor parameter names to match configuration keys (case-insensitive).

Private members are not bound, which is consistent with the reflection-based binder.

Third-party types that you don't control may need wrapper classes if the generator can't bind them directly.

Should you enable it?

If you're targeting Native AOT or using PublishTrimmed, enabling the generator is essentially required — reflection-based binding will fail or behave unpredictably.

For standard deployments on .NET 8 or later, it's a low-risk, low-effort improvement. The generator is designed to be a drop-in replacement: enable it, build, and check for any compiler warnings. If everything compiles cleanly, you've eliminated a source of reflection with no code changes.