Integration Nextjs App Router

PostHog integration for Next.js App Router

This skill helps you add PostHog analytics to Next.js App Router applications.

Workflow

Follow these steps in order to complete the integration:

1. references/1-begin.md - PostHog Setup - Begin ← Start here
2. references/2-edit.md - PostHog Setup - Edit
3. references/3-revise.md - PostHog Setup - Revise
4. references/4-conclude.md - PostHog Setup - Conclusion

Reference files

• references/EXAMPLE.md - Next.js App Router example project code
• references/1-begin.md - Start the event tracking setup process by analyzing the project and creating an event tracking plan
• references/2-edit.md - Implement PostHog event tracking in the identified files, following best practices and the example project
• references/3-revise.md - Review and fix any errors in the PostHog integration implementation
• references/4-conclude.md - Review and fix any errors in the PostHog integration implementation
• references/next-js.md - Next.js - docs
• references/identify-users.md - Identify users - docs

The example project shows the target implementation pattern. Consult the documentation for API details.

Key principles

• Environment variables: Always use environment variables for PostHog keys. Never hardcode them.
• Minimal changes: Add PostHog code alongside existing integrations. Don't replace or restructure existing code.
• Match the example: Your implementation should follow the example project's patterns as closely as possible.

Framework guidelines

• For Next.js 15.3+, initialize PostHog in instrumentation-client.ts for the simplest setup
• For feature flags, use useFeatureFlagEnabled() or useFeatureFlagPayload() hooks - they handle loading states and external sync automatically
• Add analytics capture in event handlers where user actions occur, NOT in useEffect reacting to state changes
• Do NOT use useEffect for data transformation - calculate derived values during render instead
• Do NOT use useEffect to respond to user events - put that logic in the event handler itself
• Do NOT use useEffect to chain state updates - calculate all related updates together in the event handler
• Do NOT use useEffect to notify parent components - call the parent callback alongside setState in the event handler
• To reset component state when a prop changes, pass the prop as the component's key instead of using useEffect
• useEffect is ONLY for synchronizing with external systems (non-React widgets, browser APIs, network subscriptions)
• When a reverse proxy is configured, both /static/* AND /array/* must route to the assets origin (us-assets.i.posthog.com or eu-assets.i.posthog.com).

Identifying users

Identify users during login and signup events. Refer to the example code and documentation for the correct identify pattern for this framework. If both frontend and backend code exist, pass the client-side session and distinct ID using X-POSTHOG-DISTINCT-ID and X-POSTHOG-SESSION-ID headers to maintain correlation.

Error tracking

Add PostHog error tracking to relevant files, particularly around critical user flows and API boundaries.