Pragmatic.FeatureFlags

Context-aware feature flag evaluation for .NET 10 — targeting rules, percentage rollout, and deterministic bucketing.

The Problem

Apps need runtime control over feature visibility — gradual rollouts, A/B tests, beta programs, kill switches. Plain configuration gives you on/off, but the same value applies to every user, tenant, and environment, so teams hand-roll targeting:

// Without Pragmatic: hand-rolled targeting, duplicated and inconsistent
var isEnabled = betaTenants?.Contains(tenantId) == true
    || ComputeHash(userId) % 100 < rolloutPercent;   // different result per hash/seed/rounding

That duplicates the hash-and-check pattern, gives no consistency guarantee (the same user flips between requests), has no change detection (caches serve stale toggles until restart), and conflates static configuration with context-dependent evaluation.

The Solution

Define flags with targeting rules; a deterministic evaluation engine handles the rest — stable per-user/tenant bucketing (the same input always resolves the same way), percentage rollout, and change watching.

store.Define(new FeatureFlagDefinition
{
    Name = "new-checkout",
    Enabled = false,
    Rules = [ new PercentageRule(20), new TenantRule("beta-co") ]   // 20% rollout + beta tenant
});

if (await flags.IsEnabledAsync("new-checkout", context)) { /* new path */ }

Strongly-typed flags, pluggable stores, and change notifications are all supported.

Installation

dotnet add package Pragmatic.FeatureFlags

Status

The evaluation engine, targeting rules, deterministic bucketing, strongly-typed flags, and stores are functional within the 0.8 preview. See the roadmap.

| Concepts | Evaluation engine, rule types, deterministic bucketing, vs configuration | | Getting Started | Define a flag, add targeting, evaluate it | | Stores | Pluggable backends, change watching, strongly-typed flags | | Common Mistakes | The most frequent flag pitfalls | | Troubleshooting | Problem/solution guide |

Requirements

• .NET 10.0+

License

Part of the Pragmatic.Design ecosystem — see Licensing. Pragmatic.FeatureFlags is MIT-licensed.