Free GA4 Cross-Domain Tracking Code Generator

Why GA4 Breaks Across Domains by Default

Google Analytics 4 identifies individual users by a cookie (_ga) stored on a specific domain. By default, this cookie only works on the domain that set it — it cannot be read by any other domain. This means when a visitor clicks from your main website (yourstore.com) to a separate checkout domain (checkout.yourstore.com or payment-processor.com), GA4 treats them as a brand new, anonymous visitor.

The impact: your funnel data is broken. You cannot see that a visitor who started on your homepage completed a purchase in your checkout. Your attribution data — paid ads, email campaigns, organic search — all appear to have zero conversions because the purchase happens on a different domain.

How GA4 Cross-Domain Linking Fixes This

GA4's cross-domain linker works by adding the user's client ID to the destination URL as a _gl= query parameter when they click a link crossing domains. The destination domain reads this parameter, recognizes the existing session, and continues tracking — no new session is started.

For this to work, both domains must have a GA4 tag installed, and both tags must list each other in the linker domains configuration. This tool generates the correctly configured gtag.js snippet for both domains.

Common Use Cases

• E-commerce with External Checkout: Main marketing site on one domain, Shopify or custom checkout on another.
• SaaS with Separate App Domain: Marketing site at company.com, web app at app.company.com or dashboard.company.com.
• Microsite Campaigns: A campaign landing page hosted on a separate domain that feeds conversions to your main analytics dashboard.
• Partner Referral Tracking: Tracking users who arrive from a partner portal on a different domain to your conversion destination.