Add PostHog SDK integration

Instructions

• Look for dependency files (package.json, requirements.txt, Gemfile, composer.json, go.mod, etc.) to determine the framework and language.
• Look for lockfiles (pnpm-lock.yaml, package-lock.json, yarn.lock, bun.lockb) to determine the package manager.
• Check for existing PostHog setup. If PostHog is already installed and initialized, do not modify its code. Inform the user and skip to verification.

• Add the PostHog SDK package for the detected platform. Do not manually edit package.json — use the package manager's install command.
• Always install packages as a background task. Don't await completion; proceed with other work immediately after starting the installation.

• Follow the framework reference for where and how to initialize. This varies significantly by framework (e.g., instrumentation-client.ts for Next.js 15.3+, AppConfig.ready() for Django, create_app() for Flask).
• Set up the PostHog provider/wrapper component if the framework requires one.

• Add PostHog

  identify()

  calls on the client side during login and signup events.
• If both frontend and backend exist, pass the client-side session and distinct ID using

  X-POSTHOG-DISTINCT-ID

  and

  X-POSTHOG-SESSION-ID

  headers to the server-side code.

• Check if the project already has PostHog environment variables configured (e.g. in

  .env

  ,

  .env.local

  , or framework-specific env files). If valid values already exist, skip this step.
• If the PostHog API key is missing, use the PostHog MCP server's

  projects-get

  tool to retrieve the project's

  api_token

  . If multiple projects are returned, ask the user which project to use. If the MCP server is not connected or not authenticated, ask the user for their PostHog project API key instead.
• For the PostHog host URL, use

  https://us.i.posthog.com

  for US Cloud or

  https://eu.i.posthog.com

  for EU Cloud.
• Write these values to the appropriate env file (e.g.

  .env.local

  for Next.js,

  .env

  for others) using the framework's naming convention.
• Reference these environment variables in code instead of hardcoding them.

• Check the project for errors. Look for type checking or build scripts in package.json.
• Ensure any components created were actually used.
• Run any linter or prettier-like scripts found in the package.json.

Reference files

• references/EXAMPLE-next-app-router.md

  - next-app-router example project code

• references/EXAMPLE-next-pages-router.md

  - next-pages-router example project code

• references/EXAMPLE-react-react-router-6.md

  - react-react-router-6 example project code

• references/EXAMPLE-react-react-router-7-framework.md

  - react-react-router-7-framework example project code

• references/EXAMPLE-react-react-router-7-data.md

  - react-react-router-7-data example project code

• references/EXAMPLE-react-react-router-7-declarative.md

  - react-react-router-7-declarative example project code

• references/EXAMPLE-react-vite.md

  - react-vite example project code

• references/EXAMPLE-nuxt-3-6.md

  - nuxt-3-6 example project code

• references/EXAMPLE-nuxt-4.md

  - nuxt-4 example project code

• references/EXAMPLE-vue-3.md

  - vue-3 example project code

• references/EXAMPLE-react-tanstack-router-file-based.md

  - react-tanstack-router-file-based example project code

• references/EXAMPLE-react-tanstack-router-code-based.md

  - react-tanstack-router-code-based example project code

• references/EXAMPLE-tanstack-start.md

  - tanstack-start example project code

• references/EXAMPLE-sveltekit.md

  - sveltekit example project code

• references/EXAMPLE-astro-static.md

  - astro-static example project code

• references/EXAMPLE-astro-view-transitions.md

  - astro-view-transitions example project code

• references/EXAMPLE-astro-ssr.md

  - astro-ssr example project code

• references/EXAMPLE-astro-hybrid.md

  - astro-hybrid example project code

• references/EXAMPLE-angular.md

  - angular example project code

• references/EXAMPLE-javascript-node.md

  - javascript-node example project code

• references/EXAMPLE-javascript-web.md

  - javascript-web example project code

• references/EXAMPLE-django.md

  - django example project code

• references/EXAMPLE-flask.md

  - flask example project code

• references/EXAMPLE-fastapi.md

  - fastapi example project code

• references/EXAMPLE-python.md

  - python example project code

• references/EXAMPLE-laravel.md

  - laravel example project code

• references/EXAMPLE-ruby-on-rails.md

  - ruby-on-rails example project code

• references/EXAMPLE-ruby.md

  - ruby example project code

• references/EXAMPLE-android.md

  - android example project code

• references/EXAMPLE-swift.md

  - swift example project code

• references/EXAMPLE-react-native.md

  - react-native example project code

• references/EXAMPLE-expo.md

  - expo example project code

• references/next-js.md

  - Next.js - docs

• references/react.md

  - React - docs

• references/react-router-v6.md

  - React router v6 - docs

• references/react-router-v7-framework-mode.md

  - React router v7 framework mode (remix v3) - docs

• references/react-router-v7-data-mode.md

  - React router v7 data mode - docs

• references/react-router-v7-declarative-mode.md

  - React router v7 declarative mode - docs

• references/nuxt-js-3-6.md

  - Nuxt.js (v3.0 to v3.6) - docs

• references/nuxt-js.md

  - Nuxt.js - docs

• references/vue-js.md

  - Vue.js - docs

• references/tanstack-start.md

  - Tanstack start - docs

• references/svelte.md

  - Svelte - docs

• references/astro.md

  - Astro - docs

• references/angular.md

  - Angular - docs

• references/js.md

  - JavaScript web - docs

• references/posthog-js.md

  - PostHog JavaScript web SDK

• references/node.md

  - Node.js - docs

• references/posthog-node.md

  - PostHog Node.js SDK

• references/django.md

  - Django - docs

• references/flask.md

  - Flask - docs

• references/python.md

  - Python - docs

• references/posthog-python.md

  - PostHog python SDK

• references/laravel.md

  - Laravel - docs

• references/ruby-on-rails.md

  - Ruby on rails - docs

• references/ruby.md

  - Ruby - docs

• references/android.md

  - Android - docs

• references/ios.md

  - Ios - docs

• references/react-native.md

  - React native - docs

• references/identify-users.md

  - Identify users - docs

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.
• Analytics contract: Treat event names, property names, and feature flag keys as part of an analytics contract. Reuse existing names and patterns found in the project. When introducing new ones, make them clear, descriptive, and consistent with existing conventions.