Integration Nextjs App Router — Agent Skill by PostHog

From the author

PostHog integration for Next.js App Router applications

— the description by PostHog

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides a systematic workflow for developers to integrate PostHog into Next.js App Router projects. It emphasizes best practices for client-side and server-side event tracking, user identification, and error monitoring while adhering to React-specific guidelines to ensure performance and maintainability.

What it does

Provides a multi-step workflow for PostHog setup
Defines patterns for client-side and server-side event tracking
Outlines user identification strategies for authentication flows
Offers guidance on error tracking implementation
Enforces React best practices regarding useEffect and component state
Includes reference examples for Next.js App Router integration

When to use it

When adding product analytics to a new or existing Next.js App Router project
When implementing feature flags in a Next.js application
When setting up server-side event tracking for API routes or Server Actions
When standardizing error tracking across a frontend and backend codebase

Advantages

Ensures consistent event naming and tracking patterns
Promotes clean code by discouraging misuse of useEffect
Facilitates reliable user identification across client and server boundaries
Reduces integration errors by providing a clear, step-by-step procedure

Usage examples

“How do I initialize PostHog in my Next.js App Router project?”: The agent will guide you through creating an instrumentation file and configuring the PostHog client with your project token and host.
“Where should I place event tracking code for user logins?”: The agent will instruct you to implement identification logic within your authentication context and capture server-side login events in your API routes.

Install

Download the skill as a ZIP:
https://autogineer.com/agent-skills/posthog/integration-nextjs-app-router/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip integration-nextjs-app-router.zip -d .agents/skills

Documentation by PostHog

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:

basic-integration-1.0-begin.md - PostHog Setup - Begin ← Start here
basic-integration-1.1-edit.md - PostHog Setup - Edit
basic-integration-1.2-revise.md - PostHog Setup - Revise
basic-integration-1.3-conclude.md - PostHog Setup - Conclusion

Reference files

references/EXAMPLE.md - Next.js App Router example project code
references/next-js.md - Next.js - docs
references/identify-users.md - Identify users - docs
references/basic-integration-1.0-begin.md - PostHog setup - begin
references/basic-integration-1.1-edit.md - PostHog setup - edit
references/basic-integration-1.2-revise.md - PostHog setup - revise
references/basic-integration-1.3-conclude.md - PostHog setup - conclusion

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)

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.

Files

ATTRIBUTION.mdAdded by AutoGineer987 B
LICENSELicence file added by AutoGineer1.0 KiB
SKILL.md3.0 KiB
references/EXAMPLE.md17.4 KiB
references/basic-integration-1.0-begin.md2.1 KiB
references/basic-integration-1.1-edit.md2.5 KiB
references/basic-integration-1.2-revise.md937 B
references/basic-integration-1.3-conclude.md1.6 KiB
references/identify-users.md8.1 KiB
references/next-js.md12.5 KiB

references/basic-integration-1.0-begin.md

title: PostHog Setup - Begin description: Start the event tracking setup process by analyzing the project and creating an event tracking plan

We're making an event tracking plan for this project.

Before proceeding, find any existing posthog.capture() code. Make note of event name formatting.

From the project's file list, select between 10 and 15 files that might have interesting business value for event tracking, especially conversion and churn events. Also look for additional files related to login that could be used for identifying users, along with error handling. Read the files. If a file is already well-covered by PostHog events, replace it with another option. Do not spawn subagents.

Look for opportunities to track client-side events.

IMPORTANT: Server-side events are REQUIRED if the project includes any instrumentable server-side code. If the project has API routes (e.g., app/api/**/route.ts) or Server Actions, you MUST include server-side events for critical business operations like:

Payment/checkout completion
Webhook handlers
Authentication endpoints

Do not skip server-side events - they capture actions that cannot be tracked client-side.

Create a new file with a JSON array at the root of the project: .posthog-events.json. It should include one object for each event we want to add: event name, event description, and the file path we want to place the event in. If events already exist, don't duplicate them; supplement them.

Track actions only, not pageviews. These can be captured automatically. Exceptions can be made for "viewed"-type events that correspond to the top of a conversion funnel.

As you review files, make an internal note of opportunities to identify users and catch errors. We'll need them for the next step.

Status

Before beginning a phase of the setup, you will send a status message with the exact prefix '[STATUS]', as in:

[STATUS] Checking project structure.

Status to report in this phase:

Checking project structure
Verifying PostHog dependencies
Generating events based on project

Upon completion, continue with: basic-integration-1.1-edit.md

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Security

No issues found by our static scan· No issues found

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

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Download ZIP

The ZIP holds the skill’s files, its licence files and an ATTRIBUTION.md. Download integration-nextjs-app-router.zip