How is a variation assigned in a Matomo A/B test, and does it require a server request?

When a visitor enters an A/B test for the first time, Matomo randomly assigns a variation using JavaScript in their browser. The browser determines which variation to display without requesting an assignment from the Matomo server.

Ensure a user sees the same variation

To ensure visitors see the same variation on subsequent visits, Matomo stores the assigned variation name in the browser:

• Local Storage: By default, Matomo uses the browser’s Local Storage when supported.
• Cookies: If Local Storage is unavailable, Matomo sets a cookie for up to one year to remember the assigned variation.

This allows Matomo to show the same variation when a visitor returns to your website using the same browser, provided the stored information remains available.