Remix Feature Flags installation

  1. Install the package

    Required
    Remix version

    This guide is for Remix v2. For Remix v3, see our React Router v7 docs.

    Install the PostHog JavaScript library using your package manager:

    npm install posthog-js

  2. Configure Vite

    Required

    Add posthog-js and posthog-js/react to ssr.noExternal in your vite.config.ts so they get bundled for SSR:

    vite.config.ts
    // ... imports and rest of config
    

    export default defineConfig({
      plugins: [
        remix({
          future: {
            v3_fetcherPersist: true,
            v3_relativeSplatPath: true,
            v3_throwAbortReason: true,
            v3_singleFetch: true,
            v3_lazyRouteDiscovery: true,
          },
        }),
        tsconfigPaths(),
      ],
      ssr: {
        noExternal: ["posthog-js", "posthog-js/react"],
      },
    });

  3. Create a provider

    Required

    Create a provider.tsx file in the app folder. Set up the PostHog provider to initialize after hydration:

    app/provider.tsx
    import { useEffect, useState } from "react";
    import posthog from "posthog-js";
    import { PostHogProvider } from "posthog-js/react";
    

    export function PHProvider({ children }: { children: React.ReactNode }) {
      const [hydrated, setHydrated] = useState(false);
    

      useEffect(() => {
        posthog.init("<ph_project_token>", {
          api_host: "https://us.i.posthog.com",
          defaults: "2026-01-30"
        });
    

        setHydrated(true);
      }, []);
    

      if (!hydrated) return <>{children}</>;
      return <PostHogProvider client={posthog}>{children}</PostHogProvider>;
    }

  4. Wrap your app

    Required

    Import the PHProvider component in your app/root.tsx file and use it to wrap your app:

    app/root.tsx
    // ... imports
    import { PHProvider } from "./provider";
    

    // ... links, meta, etc.
    

    export function Layout({ children }: { children: React.ReactNode }) {
      return (
        <html lang="en">
          <head>
            <meta charSet="utf-8" />
            <meta name="viewport" content="width=device-width, initial-scale=1" />
            <Meta />
            <Links />
          </head>
          <body>
            <PHProvider>
              {children}
              <ScrollRestoration />
              <Scripts />
            </PHProvider>
          </body>
        </html>
      );
    }
    

    export default function App() {
      return <Outlet />;
    }

  5. Send events

    Click around and view a couple pages to generate some events. PostHog automatically captures pageviews, clicks, and other interactions for you.

    If you'd like, you can also manually capture custom events:

    JavaScript
    posthog.capture('my_custom_event', { property: 'value' })

  6. Client-side rendering

    Required

    Basic flag implementation

    if (posthog.isFeatureEnabled('flag-key')) {
        // Do something differently for this user
        // Optional: fetch the payload
        const matchedFlagPayload = posthog.getFeatureFlagPayload('flag-key')
    }

    Multivariate flags

    if (posthog.getFeatureFlag('flag-key') == 'variant-key') { // replace 'variant-key' with the key of your variant
        // Do something differently for this user
        // Optional: fetch the payload
        const matchedFlagPayload = posthog.getFeatureFlagPayload('flag-key')
    }

  7. Server-side rendering

    Required

    Use posthog-node to evaluate feature flags on the server. Initialize PostHog in your API route or loader:

    app/api/example/route.ts
    import { PostHog } from 'posthog-node'
    

    const posthog = new PostHog(process.env.NEXT_PUBLIC_POSTHOG_PROJECT_TOKEN!, {
        host: process.env.NEXT_PUBLIC_POSTHOG_HOST
    })

    Basic flag implementation

    const isFeatureFlagEnabled = await client.isFeatureEnabled('flag-key', 'distinct_id_of_your_user')
    if (isFeatureFlagEnabled) {
        // Your code if the flag is enabled
        // Optional: fetch the payload
        const matchedFlagPayload = await client.getFeatureFlagPayload('flag-key', 'distinct_id_of_your_user', isFeatureFlagEnabled)
    }

    Multivariate flags

    const enabledVariant = await client.getFeatureFlag('flag-key', 'distinct_id_of_your_user')
    if (enabledVariant === 'variant-key') {  // replace 'variant-key' with the key of your variant
        // Do something differently for this user
        // Optional: fetch the payload
        const matchedFlagPayload = await client.getFeatureFlagPayload('flag-key', 'distinct_id_of_your_user', enabledVariant)
    }

  8. Running experiments

    Optional

    Experiments run on top of our feature flags. Once you've implemented the flag in your code, you run an experiment by creating a new experiment in the PostHog dashboard.

  9. Next steps

    Recommended

    Now that you're evaluating flags, continue with the resources below to learn what else Feature Flags enables within the PostHog platform.

    ResourceDescription
    Creating a feature flagHow to create a feature flag in PostHog
    Adding feature flag codeHow to check flags in your code for all platforms
    Framework-specific guidesSetup guides for React Native, Next.js, Flutter, and other frameworks
    How to do a phased rolloutGradually roll out features to minimize risk
    More tutorialsOther real-world examples and use cases

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