Overview

Ship feature flags on the web with OpenFeature. Local in-memory defaults, PostHog or GrowthBook in production, and the same API on client and server.

Feature flags let you turn product behavior on and off without a redeploy. Roll out a new settings page to a cohort, hide unfinished UI behind a key, or A/B test a CTA, all from one evaluation API.

TurboStarter wires this through OpenFeature so your app code stays provider-agnostic. You evaluate flags the same way whether you use the built-in in-memory provider, PostHog, or GrowthBook.

Out of the box you get:

Shared flag keys in @workspace/flags (Flag.DEMO ships as a working example)
Platform package @workspace/flags-web with client hooks and server evaluators
A FlagsProvider that syncs targeting context from the signed-in user (targetingKey, email, name)
In-memory provider as the default (no account required for local development)
Optional PostHog and GrowthBook providers, swapped by changing a few exports

The demo flag is already evaluated on Dashboard → Settings. With the default in-memory config it renders a banner that links back here, so you can confirm the pipeline before connecting a remote provider.

Architecture

Flags live in a small monorepo slice next to analytics and billing:

keys.ts - Flag key constants

in-memory.ts - Default local definitions

react.tsx - createFlagsReact + hooks

server.ts - createFlagsServer helpers

index.tsx - FlagsProvider, setContext, clearContext

server.ts - getBooleanValue, getStringValue, …

App wiring sits in apps/web/src/lib/providers/flags.tsx and is mounted with the rest of your providers. When a session appears, context is set; on logout it is cleared. PostHog uses that to identify / reset so remote rules can target real users.

Providers

Pick the backend that matches how you want to manage rollouts:

In-memory

Local defaults, zero config. Great for development.

PostHog

Flags next to analytics and monitoring.

GrowthBook

Dedicated experimentation and targeting.

Switch providers by updating the exports under packages/flags/web/src/providers. Your React and server evaluation code stays the same.

In the following sections you'll learn how to configure and use the providers.

Configuration

Choose an OpenFeature provider for web flags: in-memory for local defaults, or PostHog / GrowthBook for remote rollouts.

Usage

Evaluate feature flags on the web client and server, sync targeting context, and add new flag keys to TurboStarter.