Add Analytics (PostHog)

Use this skill when the user asks to add analytics, event tracking, page views, feature flags, or session replay to a web application.

Steps

1. Detect the framework — check for next.config.*, vite.config.*, package.json scripts, or index.html to determine if this is Next.js, React (Vite/CRA), Vue, Svelte, or plain HTML.

2. Install the SDK

   • Next.js / React: npm install posthog-js
   • Next.js (server-side): npm install posthog-js posthog-node
   • Python: pip install posthog
   • Node.js backend: npm install posthog-node

3. Create a provider / init module

   • For Next.js App Router, create app/providers.tsx:

     "use client";
     import posthog from "posthog-js";
     import { PostHogProvider as PHProvider } from "posthog-js/react";
     import { useEffect } from "react";
     
     export function PostHogProvider({ children }: { children: React.ReactNode }) {
       useEffect(() => {
         posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
           api_host: process.env.NEXT_PUBLIC_POSTHOG_HOST ?? "https://us.i.posthog.com",
           capture_pageview: false, // we capture manually for SPAs
         });
       }, []);
       return <PHProvider client={posthog}>{children}</PHProvider>;
     }

   • Wrap {children} in the root layout with <PostHogProvider>.
   • For Pages Router, init in _app.tsx inside a useEffect.
4. Add page-view tracking — for SPAs, create a component that calls posthog.capture('$pageview') on route change using the framework's router events.

5. Add .env variables — prompt the user for their PostHog project API key and host:

   NEXT_PUBLIC_POSTHOG_KEY=phc_...
   NEXT_PUBLIC_POSTHOG_HOST=https://us.i.posthog.com

   Add these keys to .env.example as well.

6. Add custom events — if the user specifies events to track (e.g. sign-up, purchase), add posthog.capture("event_name", { ...properties }) calls in the relevant handlers.
7. Feature flags (optional) — if requested, show how to use posthog.isFeatureEnabled("flag-name") or the useFeatureFlagEnabled hook.
8. Session replay (optional) — enable by adding session_recording: { maskAllInputs: false } to the init config if requested.

Notes

• Never hardcode API keys — always use environment variables.
• Add posthog-js to the Content Security Policy if the project has one.
• For monorepos, install in the package that renders the UI, not the root.