Google Analytics 4 Implementation Guide

Applies to: Any website or web app | Updated: October 2026

A practical guide for implementing Google Analytics 4 (GA4) - covering installation, critical first-time setup, event tracking, e-commerce, consent, and advanced topics. Written for AI coding assistants: skip sections that don't apply to the user's setup.

Note: Universal Analytics (UA / GA3) was fully sunset in 2024. GA4 is the only current Google Analytics product.

Section 0: Before You Start

Answer these questions before writing any code. They determine which sections apply.

Q: Are any of your visitors in the EU/EEA (European Economic Area), the UK, or Switzerland? Default: no - if yes, Consent Mode v2 setup is required (see Consent Mode v2)

Q: Do you run Google Ads (search, display, YouTube, or Shopping)? Default: no - if yes, ad consent signals matter for conversion tracking and which events you mark as key events and use as Ads conversions

Q: Is your site a single-page app (React, Vue, Angular, Next.js, etc.) where the URL changes without a full page reload? Default: check package.json for a client-side router (react-router-dom, vue-router, @angular/router, next, nuxt, @sveltejs/kit) - if found, assume SPA and apply the Single-Page Apps section automatically

Q: Do you need to track purchases or sales? Default: no - skip E-commerce Tracking if no

Q: Do you already have a GA4 property, or is this a fresh start? Default: fresh start - if fresh start, create a property at analytics.google.com before writing any code

Q: Do you use Google Tag Manager, or add the tracking code directly? Default: direct gtag.js - recommend GTM only if the user has a marketing team managing multiple tags

AI assistant: Use these answers to skip irrelevant sections. Do not implement Consent Mode unless the user confirms EEA, UK, or Swiss users, and do not implement e-commerce unless confirmed. If a SPA framework is detected, apply the SPA section and pick exactly one page_view approach (never manual page_view calls while the Enhanced Measurement history setting is still on); do not add anonymize_ip, which is a no-op in GA4 (see Common Pitfalls).

Contents

This guide is split into reference files. Use the Section 0 answers to decide which apply, then read only those; skip the rest.

• Installation: Adding GA4 to a site: gtag.js, Google Tag Manager, or Google tag gateway (first-party serving).
• Basic Configuration: Setting gtag config options such as debug mode, cookie settings, or disabling the automatic page_view.
• Critical First-Time Setup: Right after installing, before production traffic: data retention, internal and hostname filters, key events, custom dimensions.
• Common Pitfalls: Reviewing or debugging any GA4 setup; a short list of mistakes that silently break tracking.
• Event Tracking: Tracking user actions with gtag event syntax, standard events, or custom events.
• Enhanced Measurement: Deciding which events GA4 already tracks automatically before adding custom ones.
• User Properties & Custom Dimensions: Setting user properties or a User ID for cross-device tracking.
• E-commerce Tracking: The user confirmed purchase or sales tracking: view_item, add_to_cart, begin_checkout, purchase.
• Consent Mode v2: The site may have EEA, UK, or Swiss visitors, or uses a cookie or consent banner.
• Single-Page Apps: The site is a SPA and route changes must produce page_view events (Enhanced Measurement history events, manual page_view, or GTM).
• Debugging: Events are missing or wrong: DebugView, raw network requests, logging gtag calls.
• Validation & Testing: Before launch, to verify the implementation with the pre-launch checklist.
• Advanced: BigQuery Export & Sampling: Reports are sampled, raw event data is needed in BigQuery, or attribution models come up.