Feature flags in .NET without the chaos → meet Microsoft.FeatureManagement

🚦 Feature flags in .NET without the chaos → meet Microsoft.FeatureManagement (aka the “FeatureManagement” NuGet package)

Shipping a feature shouldn’t mean:

• deploying late at night
• praying nothing breaks
• or keeping a 6-month-long “WIP” branch 😅

With Microsoft.FeatureManagement you can turn features on/off at runtime using a consistent API + ASP.NET Core integrations.

✅ What it gives you

• A clean way to define flags (config, Azure App Configuration, etc.)
• Code-level gating via IFeatureManager (no “if spaghetti”)
• ASP.NET Core gating with [FeatureGate] for controllers/pages/endpoints
• Feature filters for real rollouts (targeting, time window, percentages)

⚡ Quick setup (ASP.NET Core)

Install:

• Microsoft.FeatureManagement
• Microsoft.FeatureManagement.AspNetCore

appsettings.json

{
  "FeatureManagement": {
    "NewCheckout": true
  }
}

Program.cs

builder.Services.AddFeatureManagement();

Use it in code

app.MapGet("/checkout", async (IFeatureManager fm) =>
{
    if (await fm.IsEnabledAsync("NewCheckout"))
        return Results.Ok("✅ New checkout");

    return Results.Ok("⬅️ Old checkout");
});

Or gate an endpoint/page

[FeatureGate("NewCheckout")]
public class CheckoutController : Controller { }

🌩️ Pro move: Azure App Configuration

If you want centralized flags + refresh without redeploy, Azure App Configuration integrates directly (and supports feature filters + refresh intervals).

When to use (✅) vs when not to (❌)

✅ Use it for:

• gradual rollouts (percentage / targeting)
• “dark launches”
• A/B experiments
• emergency kill switches
• decoupling deploy from release

❌ Avoid it for:

• permanent business rules (“VIPs always…”)
• long-lived flags that never get removed
• security boundaries (flags reduce exposure, but don’t replace authorization)

Best practices (the stuff that saves you later)

• Name flags like products, not tech (Checkout.NewFlow, Billing.TaxesV2)
• Set an owner + removal date
• Test both paths
• Delete dead flags (flag graveyards are real)