Don't have one? Create one ↗
The Happy TaggerThe Happy Tagger
← All courses

Lesson 1 of 3

Cross-Domain Linker

① Connect your GTM container

Paste your container ID to load it into this page. It only ever runs here.

Advanced: use a specific environment

GA4 identifies a session with a client ID stored in a first-party cookie, and cookies don't cross domains. So when a visitor moves from yourdomain.com to a checkout on shop.example.com, GA4 would normally start a brand-new session and lose the source that drove it, attribution broken at the worst moment.

Cross-domain measurement fixes this. List both domains in your Google tag and GA4's linker decorates outgoing links with a _gl parameter that carries the client ID across. The destination reads _gl and continues the same session.

The button below points at a different domain. Configure the linker, then confirm the outgoing URL gains a _gl= parameter.

Goal

Configure cross-domain measurement so the GA4 session survives the hop to a second domain.

Build it in GTM

  1. Open your Google tag

    Go to Tags and open your Google tag (or GA4 Configuration). Cross-domain settings live on the tag that loads GA4.

  2. Configure your domains

    1. Open Configuration settings → Configure your domains (under cross-domain).
    2. Add every domain in the journey, e.g. yourdomain.com and shop.example.com.
    3. Save. GA4 now decorates links between those domains automatically.

  3. Confirm the _gl parameter

    Hover or inspect a link to the other domain: it should gain a _gl= parameter. That's the linker passing the client ID across.

Debug in Tag Assistant

Copy this lesson's live URL and paste it into GTM Preview, that is the page Tag Assistant connects to. It has the clickable elements, so this page stays clean for reading.

  1. In your GTM, click Preview.
  2. Paste the live URL above and click Connect.
  3. Interact with the live page and watch your tag fire in Tag Assistant.

What you should expect to see

With the linker configured, clicks to shop.example.com carry a _gl= parameter, and GA4 continues one session instead of starting a new one.

Verify your container

Built it? Export your container, Admin → Export Container, choose your workspace, then drop the JSON here to check it against this lesson.

Drop your container .json here

or browse · checked in your browser, nothing is uploaded

0 of 3 lessons complete