React Router V7 framework mode (Remix V3)

First, you'll need to install posthog-js and @posthog/react using your package manager. These packages allow you to capture client-side events.

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

In framework mode, you'll also need to set posthog-js and @posthog/react as external packages in your vite.config.ts file to avoid SSR errors.

// ... imports

export default defineConfig({
  plugins: [tailwindcss(), reactRouter(), tsconfigPaths()],
  ssr: {
    noExternal: ['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. If you're using Vite, including VITE_PUBLIC_ in their names ensures they are accessible in the frontend.

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

In framework mode, your app enters from the app/entry.client.tsx file. In this file, you'll need to initialize the PostHog SDK and pass it to your app through the PostHogProvider context.

import { startTransition, StrictMode } from "react";
import { hydrateRoot } from "react-dom/client";
import { HydratedRouter } from "react-router/dom";

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', 
  __add_tracing_headers: [ window.location.host, 'localhost' ], 
}); 


startTransition(() => {
  hydrateRoot(
    document,
    {/* Pass PostHog client through PostHogProvider */}
    <PostHogProvider client={posthog}> 
      <StrictMode>
        <HydratedRouter />
      </StrictMode>
    </PostHogProvider>, 
  );
});

To help PostHog track your user sessions across the client and server, you'll need to add the __add_tracing_headers: ['your-backend-domain1.com', 'your-backend-domain2.com', ...] option to your PostHog initialization. This adds the X-POSTHOG-DISTINCT-ID and X-POSTHOG-SESSION-ID headers to your requests, which we'll later use on the server-side.

useEffect(() => {
  posthog?.capture('test') // using optional chaining (recommended)

  if (posthog) {
    posthog.capture('test') // using an if statement
  }
}, [posthog])

At this point, you should be able to capture client-side events and see them in your PostHog project. This includes basic events like page views and button clicks that are autocaptured.

You can also try to capture a custom event to verify it's working. You can access PostHog in any component using the usePostHog hook.

import { usePostHog } from '@posthog/react'

function App() {
  const posthog = usePostHog()
  return <button onClick={() => posthog?.capture('button_clicked')}>Click me</button>
}

You should see these events in a minute or two in the activity tab.

On the client-side, you can access the PostHog client using the usePostHog hook. This hook returns the initialized PostHog client, which you can use to call PostHog methods. For example:

import { usePostHog } from '@posthog/react'

function App() {
  const posthog = usePostHog()
  return <button onClick={() => posthog?.capture('button_clicked')}>Click me</button>
}

For a complete list of available methods, see the posthog-js documentation.

Now that you can capture basic client-side events, you'll want to identify your user so you can associate users with captured events.

Generally, you identify users when they log in or when they input some identifiable information (e.g. email, name, etc.). You can identify users by calling the identify method on the PostHog client:

export default function Login() {
  const { user, login } = useAuth();
  const posthog = usePostHog();  

  const handleLogin = async (e: React.FormEvent) => {
    // existing code to handle login...
    const user = await login({ email, password });

    posthog?.identify(user.email, 
      { 
        email: user.email, 
        name: user.name, 
      } 
    ); 
    posthog?.capture('user_logged_in'); 
  };

  return (
    <div>
      {/* ... existing code ... */}
      <button onClick={handleLogin}>Login</button>
    </div>
  );
}

PostHog automatically generates anonymous IDs for users before they're identified. When you call identify, a new identified person is created. All previous events tracked with the anonymous ID link to the new identified distinct ID, and all future captures on the same browser associate with the identified person.

PostHog can capture exceptions thrown in your app through an error boundary. React Router in framework mode has a built-in error boundary that you can use to capture exceptions. You can create an error boundary by exporting ErrorBoundary from your app/root.tsx file.

import { usePostHog } from '@posthog/react'

export function ErrorBoundary({ error }: Route.ErrorBoundaryProps) {
  const posthog = usePostHog();
  posthog?.captureException(error);

  // other error handling code...
  return (
    <div>
      <h1>Something went wrong</h1>
      <p>{error.message}</p>
    </div>
  );
}

This automatically captures exceptions thrown in your React Router app using the posthog.captureException() method.

The PostHogCaptureOnViewed component enables you to automatically capture events when elements scroll into view in the browser. This is useful for tracking impressions of important content, monitoring user engagement with specific sections, or understanding which parts of your page users are actually seeing.

The component wraps your content and sends a $element_viewed event to PostHog when the wrapped element becomes visible in the viewport. It only fires once per component instance.

Basic usage:

import { PostHogCaptureOnViewed } from '@posthog/react'

function App() {
    return (
        <PostHogCaptureOnViewed name="hero-banner">
            <div>Your important content here</div>
        </PostHogCaptureOnViewed>
    )
}

With custom properties:

You can include additional properties with the event to provide more context:

<PostHogCaptureOnViewed
    name="product-card"
    properties={{ 
        product_id: '123', 
        category: 'electronics',
        price: 299.99
    }}
>
    <ProductCard />
</PostHogCaptureOnViewed>

Tracking multiple children:

Use trackAllChildren to track each child element separately. This is useful for galleries or lists where you want to know which specific items were viewed:

<PostHogCaptureOnViewed
    name="product-gallery"
    properties={{ gallery_type: 'featured' }}
    trackAllChildren
>
    <ProductCard id="1" />
    <ProductCard id="2" />
    <ProductCard id="3" />
</PostHogCaptureOnViewed>

When trackAllChildren is enabled, each child element sends its own event with a child_index property indicating its position.

Custom intersection observer options:

You can customize when elements are considered "viewed" by passing options to the IntersectionObserver:

<PostHogCaptureOnViewed
    name="footer"
    observerOptions={{ 
        threshold: 0.5,  // Element is 50% visible
        rootMargin: '0px'
    }}
>
    <Footer />
</PostHogCaptureOnViewed>

The component passes all other props to the wrapper div, so you can add styling, classes, or other HTML attributes as needed.

Install the PostHog Node SDK using your package manager. This is the SDK you'll use to capture server-side events.

npm install posthog-node --save

yarn add posthog-node

pnpm add posthog-node

bun add posthog-node

Next, create a server-side middleware to help you capture server-side events. This middleware helps you achieve the following:

• Initialize a PostHog client
• Fetch the session and distinct ID from the X-POSTHOG-SESSION-ID and X-POSTHOG-DISTINCT-ID headers and pass them to your request as a context. This automatically identifies the user and session for you in all subsequent event captures.
• Calls shutdown() on the PostHog client to ensure all events are sent before the request is completed.

import { PostHog } from "posthog-node";
import type { RouterContextProvider } from "react-router";
import type { Route } from "../+types/root";

export interface PostHogContext extends RouterContextProvider {
  posthog?: PostHog;
}

export const posthogMiddleware: Route.MiddlewareFunction = async ({ request, context }, next) => {
  const posthog = new PostHog(process.env.VITE_PUBLIC_POSTHOG_KEY!, {
    host: process.env.VITE_PUBLIC_POSTHOG_HOST!,
    flushAt: 1,
    flushInterval: 0,
  });

  const sessionId = request.headers.get('X-POSTHOG-SESSION-ID');
  const distinctId = request.headers.get('X-POSTHOG-DISTINCT-ID');

  (context as PostHogContext).posthog = posthog;

  const response = await posthog.withContext(
    { sessionId: sessionId ?? undefined, distinctId: distinctId ?? undefined },
    next
  );

  await posthog.shutdown().catch(() => {});

  return response;
};

Then, you'll need to register the middleware in your app in the app/root.tsx file by exporting it in the Route.MiddlewareFunction[] array.

import { posthogMiddleware } from './lib/posthog-middleware';

export const middleware: Route.MiddlewareFunction[] = [
  posthogMiddleware,
  // other middlewares...
];

At this point, you should be able to capture server-side events and see them in your PostHog project.

In a route, you can access the PostHog client from the context and capture an event. The middleware assigns the session ID and the distinct ID. This ensures that the system associates events with the correct user and session.

import type { PostHogContext } from "../lib/posthog-middleware";

export async function action({ request, context }: Route.ActionArgs) {
  const body = await request.json();
  // ... existing code ...

  // Access the PostHog client from the context and capture an event
  const posthog = (context as PostHogContext).posthog;
  posthog?.capture({ event: 'checkout_completed' });
  
  return Response.json({ 
    success: true, 
    // ... existing code ...
  });
}

Now that you've set up PostHog for React Router, you can start capturing events and exceptions in your app.

To get the most out of PostHog, you should familiarize yourself with the following:

• PostHog Web SDK docs: Learn more about the PostHog Web SDK and how to use it on the client-side.
• PostHog Node SDK docs: Learn more about the PostHog Node SDK and how to use it on the server-side.
• Identify users: Learn more about how to identify users in your app.
• Group analytics: Learn more about how to use group analytics in your app.
• PostHog AI: After capturing events, use PostHog AI to help you understand your data and build insights.
• Feature flags and experiments: Feature flag and experiment setup is the same as React. You can find more details in the React integration guide.