PostHog Analytics Skill

Load with: base.md + [framework].md

For implementing product analytics with PostHog - event tracking, user identification, feature flags, and project-specific dashboards.

Sources: PostHog Docs | Product Analytics | Feature Flags

Philosophy

Measure what matters, not everything.

Analytics should answer specific questions:

Are users getting value? (activation, retention)
Where do users struggle? (funnels, drop-offs)
What features drive engagement? (feature usage)
Is the product growing? (acquisition, referrals)

Don't track everything. Track what informs decisions.

Installation

Next.js (App Router)

npm install posthog-js

// lib/posthog.ts
import posthog from 'posthog-js';

export function initPostHog() {
  if (typeof window !== 'undefined' && !posthog.__loaded) {
    posthog.init(process.env.NEXT_PUBLIC_POSTHOG_KEY!, {
      api_host: process.env.NEXT_PUBLIC_POSTHOG_HOST || 'https://us.i.posthog.com',
      person_profiles: 'identified_only', // Only create profiles for identified users
      capture_pageview: false, // We'll handle this manually for SPA
      capture_pageleave: true,
      loaded: (posthog) => {
        if (process.env.NODE_ENV === 'development') {
          posthog.debug();
        }
      },
    });
  }
  return posthog;
}

export { posthog };

// app/providers.tsx
'use client';

import { useEffect } from 'react';
import { usePathname, useSearchParams } from 'next/navigation';
import { initPostHog, posthog } from '@/lib/posthog';

export function PostHogProvider({ children }: { children: React.ReactNode }) {
  const pathname = usePathname();
  const searchParams = useSearchParams();

  useEffect(() => {
    initPostHog();
  }, []);

  // Track pageviews
  useEffect(() => {
    if (pathname) {
      let url = window.origin + pathname;
      if (searchParams.toString()) {
        url += `?${searchParams.toString()}`;
      }
      posthog.capture('$pageview', { $current_url: url });
    }
  }, [pathname, searchParams]);

  return <>{children}</>;
}

// app/layout.tsx
import { PostHogProvider } from './providers';

export default function RootLayout({ children }: { children: React.ReactNode }) {
  return (
    <html lang="en">
      <body>
        <PostHogProvider>
          {children}
        </PostHogProvider>
      </body>
    </html>
  );
}

React (Vite/CRA)

// src/posthog.ts
import posthog from 'posthog-js';

posthog.init(import.meta.env.VITE_POSTHOG_KEY, {
  api_host: import.meta.env.VITE_POSTHOG_HOST || 'https://us.i.posthog.com',
  person_profiles: 'identified_only',
});

export { posthog };

// src/main.tsx
import { PostHogProvider } from 'posthog-js/react';
import { posthog } from './posthog';

ReactDOM.createRoot(document.getElementById('root')!).render(
  <PostHogProvider client={posthog}>
    <App />
  </PostHogProvider>
);

Python (FastAPI/Flask)

pip install posthog

# analytics/posthog_client.py
import posthog
from functools import lru_cache

@lru_cache()
def get_posthog():
    posthog.project_api_key = os.environ["POSTHOG_API_KEY"]
    posthog.host = os.environ.get("POSTHOG_HOST", "https://us.i.posthog.com")
    posthog.debug = os.environ.get("ENV") == "development"
    return posthog

# Usage
def track_event(user_id: str, event: str, properties: dict = None):
    ph = get_posthog()
    ph.capture(
        distinct_id=user_id,
        event=event,
        properties=properties or {}
    )

def identify_user(user_id: str, properties: dict):
    ph = get_posthog()
    ph.identify(user_id, properties)

Node.js (Express/Hono)

npm install posthog-node

// lib/posthog.ts
import { PostHog } from 'posthog-node';

const posthog = new PostHog(process.env.POSTHOG_API_KEY!, {
  host: process.env.POSTHOG_HOST || 'https://us.i.posthog.com',
});

// Flush on shutdown
process.on('SIGTERM', () => posthog.shutdown());

export { posthog };

// Usage
export function trackEvent(userId: string, event: string, properties?: Record<string, any>) {
  posthog.capture({
    distinctId: userId,
    event,
    properties,
  });
}

export function identifyUser(userId: string, properties: Record<string, any>) {
  posthog.identify({
    distinctId: userId,
    properties,
  });
}

Environment Variables

# .env.local (Next.js) - SAFE: These are meant to be public
NEXT_PUBLIC_POSTHOG_KEY=phc_xxxxxxxxxxxxxxxxxxxx
NEXT_PUBLIC_POSTHOG_HOST=https://us.i.posthog.com

# .env (Backend) - Keep private
POSTHOG_API_KEY=phc_xxxxxxxxxxxxxxxxxxxx
POSTHOG_HOST=https://us.i.posthog.com

Add to credentials.md patterns:

'POSTHOG_API_KEY': r'phc_[A-Za-z0-9]+',

User Identification

When to Identify

// Identify o

...

posthog-analytics

SKILL.md