FeatBit .NET Server SDK

When to Use This Skill

Use for server-side .NET applications — Console apps, Web API, Worker Services, and ASP.NET Core — that need real-time feature flag evaluation.

Why server-side SDK: establishes one persistent streaming connection, evaluates all flags locally, and returns results with near-zero latency on each call. Do not use for Blazor WebAssembly or MAUI — those require a client-side SDK.

Source

https://github.com/featbit/featbit-dotnet-sdk

Setup Workflow

Copy and track progress:

Step 1: Install the package
Step 2: Initialize the client
Step 3: Evaluate the first feature flag
Step 4: If this is ASP.NET Core, switch to dependency injection
Step 5: If advanced behavior is needed, read the specific reference or README section

Step 1: Install the package

Run:

dotnet add package FeatBit.ServerSdk

Step 2: Initialize the client

Use this minimal setup:

using FeatBit.Sdk.Server;
using FeatBit.Sdk.Server.Model;
using FeatBit.Sdk.Server.Options;

var options = new FbOptionsBuilder("<your-env-secret>")
  .Streaming(new Uri("ws://localhost:5100"))
  .Event(new Uri("http://localhost:5100"))
  .Build();

var client = new FbClient(options);
var user = FbUser.Builder("anonymous").Build();
var flagValue = client.BoolVariation("flag-key", user, defaultValue: false);
await client.CloseAsync();

Step 3: Validate the integration

If client.Initialized is false or the first variation returns the fallback unexpectedly, verify EnvSecret, Streaming URI, and Event URI, then retry.

Step 4: If this is ASP.NET Core, use dependency injection

Why: ensures a single FbClient is shared across the application lifetime and is disposed automatically when the host shuts down.

Use this pattern:

using FeatBit.Sdk.Server.DependencyInjection;

builder.Services.AddFeatBit(options =>
{
  options.EnvSecret = "<your-env-secret>";
  options.StreamingUri = new Uri("ws://localhost:5100");
  options.EventUri = new Uri("http://localhost:5100");
});

Inject IFbClient where feature flag evaluation is needed.

Feature Flag Evaluation

After the client is initialized, evaluate a feature flag with a user and a fallback value:

const string flagKey = "game-runner";
var user = FbUser.Builder("anonymous").Build();

var boolVariation = client.BoolVariation(flagKey, user, defaultValue: false);
var boolVariationDetail = client.BoolVariationDetail(flagKey, user, defaultValue: false);

Use BoolVariation when only the flag value is needed. Use BoolVariationDetail when the user also asks why a value was returned.

User Custom Properties

Add custom properties to FbUser when targeting rules depend on user attributes beyond key and name:

var user = FbUser.Builder("a-unique-key-of-user")
  .Name("bob")
  .Custom("age", "15")
  .Custom("country", "FR")
  .Build();

Use built-in properties for stable identity fields. Use Custom(key, value) for targeting attributes that must be referenced in feature flag rules.