React feature flags installation

For Next.js, we recommend following the Next.js integration guide instead.

Install posthog-js and @posthog/react using your package manager:

npm install --save posthog-js @posthog/react
yarn add posthog-js @posthog/react
pnpm add posthog-js @posthog/react
bun add posthog-js @posthog/react

Add your environment variables to your .env.local file and to your hosting provider (e.g. Vercel, Netlify, AWS). You can find your project API key and host in your project settings. Including VITE_PUBLIC_ in their names ensures they are accessible in the frontend.

.env.local
VITE_PUBLIC_POSTHOG_KEY=<ph_project_api_key>
VITE_PUBLIC_POSTHOG_HOST=https://us.i.posthog.com

Integrate PostHog at the root of your app (such as main.jsx if you are using Vite).

React
// src/main.jsx
import { StrictMode } from 'react'
import { createRoot } from 'react-dom/client'
import './index.css'
import App from './App.jsx'
import posthog from 'posthog-js';
import { PostHogProvider } from '@posthog/react'

posthog.init(import.meta.env.VITE_PUBLIC_POSTHOG_KEY, {
  api_host: import.meta.env.VITE_PUBLIC_POSTHOG_HOST,
  defaults: '2025-11-30',
});

createRoot(document.getElementById('root')).render(
  <StrictMode>
    <PostHogProvider client={posthog}>
      <App />
    </PostHogProvider>
  </StrictMode>,
)

Don't directly import PostHog

Do not directly import posthog apart from installation as shown above. This will likely cause errors as the library might not be initialized yet. Initialization is handled automatically when you use the PostHogProvider and usePostHog hook.

Using React Router v7?

You need to set posthog-js and @posthog/react as external packages in your vite.config.ts file to avoid SSR errors.

vite.config.ts
// ... imports

export default defineConfig({
  plugins: [tailwindcss(), reactRouter(), tsconfigPaths()],
  ssr: {
    noExternal: ['posthog-js', '@posthog/react']
  }
});

See our Remix docs for more details.

Next steps

Resource	Description
Adding feature flag code	How to check flags in your code for all platforms
Framework-specific guides	Setup guides for React Native, Next.js, Flutter, and other frameworks
How to do a phased rollout	Gradually roll out features to minimize risk
More tutorials	Other real-world examples and use cases

React feature flags installation

Next steps

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