Feature flags for the whole team.

Browsers, Node, Cloudflare Workers and Vercel Edge. Zero dependencies, about 12 KB gzipped.

import { FlagClient } from '@featflags/js'

const flags = new FlagClient({
  key: 'pk_live_…',
  cdnUrl: 'https://flags.featflags.io',
  context: { kind: 'user', key: userId, plan: 'pro' },
})

if (flags.bool('new-checkout', false)) showNewCheckout()

Provider and hooks, with server rendering.

import { FeatflagsProvider, useFlag } from '@featflags/react'

<FeatflagsProvider options={{ key: 'pk_live_…', cdnUrl: 'https://flags.featflags.io' }} context={{ key: user.id }}>
  <App />
</FeatflagsProvider>

function Checkout() {
  return useFlag('new-checkout', false) ? <NewCheckout /> : <OldCheckout />
}

React Native 0.74+, with the React hooks. Starts from the last flags it saw, even offline.

import { createClient, FeatflagsProvider, useFlag, type FlagClient } from '@featflags/react-native'

const flags = createClient({ key: 'pk_live_…', cdnUrl: 'https://flags.featflags.io' })

export function App() {
  const [client, setClient] = useState<FlagClient>()
  useEffect(() => void flags.then(setClient), [])
  if (!client) return null
  return <FeatflagsProvider client={client} context={{ key: user.id }}><Home /></FeatflagsProvider>
}

function Checkout() {
  return useFlag('new-checkout', false) ? <NewCheckout /> : <OldCheckout />
}

Standard library only. OpenFeature provider in its own module.

flags, err := featflags.New(ctx, featflags.Config{
	Key:    "sk_live_…",
	CDNURL: "https://flags.featflags.io",
})
user := featflags.NewContext(map[string]any{"key": userID, "plan": "pro"})
if flags.Bool(ctx, "new-checkout", user, false) { … }

Standard library only. OpenFeature provider behind an extra.

flags = featflags.Client("sk_live_…", "https://flags.featflags.io")

if flags.bool_variation("new-checkout", {"key": user_id, "plan": "pro"}, False):
    ...

Java 17+ and Kotlin on servers, Jackson only. OpenFeature provider included.

var flags = FeatflagsClient.builder("sk_live_…", "https://flags.featflags.io").build();

if (flags.boolVariation("new-checkout", Context.of(Map.of("key", userId)), false)) { … }

Async, with an on-disk cache so your service starts even when we can’t be reached.

let flags = featflags::Client::builder("https://flags.featflags.io", "sk_live_…")
    .build()
    .await;
let ctx = featflags::context(json!({ "key": user_id, "plan": "pro" }));
if flags.bool("new-checkout", &ctx, false) { … }

.NET 8+, base class library only. OpenFeature provider included.

await using var flags = await FeatFlagsClient.CreateAsync(new FeatFlagsOptions
{
    Key = "sk_live_…",
    CdnUrl = "https://flags.featflags.io",
});
var user = Context.Of(new Dictionary<string, object?> { ["key"] = userId, ["plan"] = "pro" });
if (flags.BoolVariation("new-checkout", user, false)) { … }

Standard library only. Works under Puma and Unicorn without extra setup.

flags = Featflags::Client.new("sk_live_…", "https://flags.featflags.io")

if flags.bool_variation("new-checkout", { key: user.id, plan: "pro" }, false)
  # …
end

PHP 8.2+. A request never waits for us once your servers have the flags.

$flags = new Featflags\Client('sk_live_…', 'https://flags.featflags.io');

if ($flags->boolVariation('new-checkout', ['key' => $userId, 'plan' => 'pro'], false)) {
    // …
}

Add it to your supervision tree. Flags are read in the calling process.

children = [
  {Featflags, name: MyApp.Flags, key: "sk_live_…", cdn_url: "https://flags.featflags.io"}
]

if Featflags.bool_variation(MyApp.Flags, "new-checkout", %{key: user.id}, false) do
  # …
end

Swift, for iOS and macOS. Starts from the last flags it saw, even offline.

var options = FlagClient.Options(key: "pk_live_…", cdnURL: URL(string: "https://flags.featflags.io")!)
options.context = ["key": user.id, "plan": "pro"]
let flags = FlagClient(options)

if flags.bool("new-checkout", default: false) { … }

Kotlin, minSdk 24. Starts from the last flags it saw, even offline.

val flags = FeatflagsClient.android(app, FeatflagsOptions(key = "pk_live_…", cdnUrl = "https://flags.featflags.io"))

flags.identify(Context.user(user.id, mapOf("plan" to "pro")))
if (flags.bool("new-checkout", false)) { … }

Dart, for Flutter apps, Flutter web and Dart programs. Widgets rebuild when a flag changes.

final flags = FlagClient(FlagClientOptions(
  key: 'pk_live_…',
  cdnUrl: Uri.parse('https://flags.featflags.io'),
  context: {'key': user.id, 'plan': 'pro'},
));
runApp(FeatFlagsProvider(client: flags, child: const App()));

// In build:
FeatFlagsProvider.of(context).boolValue('new-checkout', false) ? const NewCheckout() : const Checkout()