[GA4] Set up cross-domain measurement

Cross-domain measurement allows activity to be accurately attributed to a single user as they cross domains. Outbound clicks that would ordinarily trigger an event via enhanced measurement are ignored when the outbound link leads to a domain that you've listed as part of cross-domain measurement.

Video overview

Cookies and cross-domain measurement

When there is consent, Analytics uses first-party cookies to set IDs for each unique user and each unique session.

• Without cross-domain measurement, new cookies with new IDs are created for each domain a user visits. As a result, a single user visiting different root domains (e.g. example.com and anotherexample.com) on the same device will be identified separately (two users and two sessions instead of one user and one session).
• With cross-domain measurement, the cookies retain the same IDs as they are passed from one domain to another via a URL parameter (_gl) when the user navigates between domains through a link or a form. As a result, Analytics identifies just one user and one session.

Set up cross-domain measurement via Admin

1. In Admin, under Data collection and modification, click Data streams.
   Note: The previous link opens to the last Analytics property you accessed. You can change the property using the property selector. You must be an Editor or above to set up cross-domain measurement, and you can create up to 100 conditions.
2. Click Web, then click a web data stream.
3. In the web stream details, click Configure tag settings (at the bottom).
4. In the Settings section, click Configure your domains.
5. If you use the same Google tag across domains, they are automatically detected and show up in the Recommendations section. To accept a recommendation, click Add.
   To manually add a domain, click Add condition under Include domains that match the following conditions:
   • Choose a match type.
   • Under Domain, enter the identifier for the domain you want to match (e.g., example.com).
   • Add each domain you want to include in cross-domain measurement.
   Conditions are evaluated using OR logic.
6. Click Save.

Manual setup

  
gtag('get', 'TAG_ID', 'client_id', (client_id) => {
  // Store the client ID in a variable.
});
gtag('get', 'TAG_ID', 'session_id', (session_id) => {
  // Store the session ID in a variable.
});

  

gtag('config','TAG_ID', {
'client_id': getClientIdFromUrl(),
'session_id': getSessionIdFromUrl()
});
  

Verify that cross-domain measurement is working properly

Cross-domain measurement works by appending parameters to the URLs on your website. In rare cases, your web server might run into an error, such as returning a 5xx error response code or failing to start a download.

To verify cross-domain measurement works:

1. Open a page of your site that contains a link or a form that points to a domain you configured for cross-domain measurement.
2. Click the link or submit the form to navigate to the destination domain.
3. Verify that the page loads correctly.
4. Verify that the URL in the destination domain contains the linker parameter _gl. For example: https://example.com/?_gl=1*abcde5*.
5. If your website provides any downloads: Navigate to a page with the linking parameter in the URL and start a download. Verify that the download starts successfully.

If you encounter an error, try Troubleshooting cross-domain measurement.

Troubleshooting

If you can't confirm the presence of the parameter _gl in the URL of the destination domain per the steps above, double check that the domain you configured in the interface matches the domain your site is pointing to.

It's also possible that your website is configured in a way that prevents cross-domain measurement from working correctly. With the help of an experienced web developer, investigate whether your website is being affected by the following issues.

URL redirects

If the destination page redirects or doesn't support arbitrary query parameters, the parameter _gl may end up being removed from the URL even if it was appended by Analytics in the previous page. (This usually happens too quickly to observe by eye.) To confirm if this is happening to your site, check the network requests made by the previous page using the Chrome Developer Tools. To fix this issue, configure your site to preserve the parameter _gl in redirects.

Conflicts with other scripts

Cross-domain measurement works by creating an event listener on the document node of a page. When users click a link, the click event bubbles up to the document node and the parameter _gl is added to the link URL. This process cannot work properly in the following scenarios:

• When the navigation is triggered by JavaScript as opposed to a direct response to a user action.
• When competing scripts in the page stop the event propagation before it reaches the document node; for example, when Event.stopPropagation() is used.