Feature Flags in C#: How to Enable Features Without Redeployment

What Are Feature Flags and Why You Need Them

Imagine: you've written a cool new feature — for example, smart search with autocomplete. Everything is tested, the code has passed review. But you're not 100% sure users will accept it. Or you're afraid it will fail under load. What to do?

In the past, the answer was simple: "Deploy to production and pray." Today we are smarter. We use feature flags (feature toggles) — a mechanism that allows you to enable and disable functionality on the fly, without recompilation or redeployment.

In this article on PythonLib, we'll explore how to implement feature flags in C# projects — from the simplest implementation to advanced scenarios with A/B testing and canary releases.

Why Feature Flags Are a Must-Have for C# Developers

Feature flags C# solve three key tasks:

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• Safe deployment: Deploy code to production even if the feature isn't ready yet. Just disable the flag.
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• Instant disabling: Something went wrong? One click in the admin panel — and the problematic feature disappears.
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• Flexible feature management: Enable features for specific users, regions, or by time.
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And the best part: for feature management in .NET, you don't need to reinvent the wheel — there's a ready-made library Microsoft.FeatureManagement.

The Simplest Way: Configuration File

Let's start with a basic approach — via appsettings.json. This is ideal for simple feature toggles .NET.

Step 1. Add Settings

{\n  "FeatureManagement": {\n    "NewSearchEngine": true,\n    "DarkMode": false,\n    "BetaDashboard": true\n  }\n}

Step 2. Register the Service

In Program.cs, add:

builder.Services.AddFeatureManagement();

Step 3. Use in Code

public class SearchController\n{\n    private readonly IFeatureManager _featureManager;\n\n    public SearchController(IFeatureManager featureManager)\n    {\n        _featureManager = featureManager;\n    }\n\n    public async Task<IActionResult> Search(string query)\n    {\n        if (await _featureManager.IsEnabledAsync("NewSearchEngine"))\n        {\n            return View("NewSearch", await _newEngine.SearchAsync(query));\n        }\n        return View("LegacySearch", await _oldEngine.SearchAsync(query));\n    }\n}

Done! Now, to enable a new feature, just change true to false in the config and restart the application. But we want to do it without a restart, right?

Dynamic Feature Flags: Switching Without Restart

For conditional features C# without reloading, use configuration providers that load changes. The best option is a database or Redis.

Create a Provider from a Database

public class DatabaseFeatureDefinitionProvider : IFeatureDefinitionProvider\n{\n    private readonly AppDbContext _db;\n\n    public DatabaseFeatureDefinitionProvider(AppDbContext db)\n    {\n        _db = db;\n    }\n\n    public async Task<FeatureDefinition> GetFeatureDefinitionAsync(string featureName)\n    {\n        var feature = await _db.FeatureFlags\n            .FirstOrDefaultAsync(f => f.Name == featureName);\n        \n        return feature != null \n            ? new FeatureDefinition { Name = feature.Name, EnabledFor = feature.EnabledFor }\n            : null;\n    }\n\n    public IAsyncEnumerable<FeatureDefinition> GetAllFeatureDefinitionsAsync()\n    {\n        return _db.FeatureFlags\n            .Select(f => new FeatureDefinition { Name = f.Name, EnabledFor = f.EnabledFor })\n            .AsAsyncEnumerable();\n    }\n}

Register it:

builder.Services.AddFeatureManagement