Cross-domain A/B testing: count the sale on the other site

What’s new

Cross-domain A/B testing follows a visitor from the site where a test runs to another site you own, and counts the conversion that happens there. Since 18 October 2026, a Cuttl test can do this: a visitor who clicks through to a linked site sees the same version there, and a purchase or sign-up on that site counts in the test. It is live now on the Max plan.

Why it matters

Many sites finish the journey somewhere else: a store with its checkout on a separate domain, a marketing site that sends sign-ups to an app, or a brand with one domain per country. A test that stops at the first domain misses the purchase or sign-up on the second.

Without a link between the domains, the second site treats every arrival as a new visitor. The test either has to judge a version on clicks to the other site, which don’t always turn into orders, or the team stitches reports together by hand.

With the domains linked, the primary goal can be a paid order on the checkout domain, and every version is judged on it.

How it works

Cross-domain tests connect sites that already sit in the same Cuttl workspace:

• Add each domain as a site in the workspace, with its domain set and the Cuttl Tag on its pages.
• In Web Experiments, open A/B settings from the experiments list, go to Cross-domain tests, tick the other sites and save.
• Create a test on the first site as usual, and pick a goal that happens on the linked site, such as a purchase.

When a visitor in the test clicks a normal link to a linked site, the link carries their test versions across, and the visitor sees the same version on the other side. Each site keeps its own visitor IDs, and Cuttl links them for the test. Subdomains of a linked domain count too.

The report shows conversions from both sites, in the same place as any other test. For background on reading it, see what A/B testing is and the guide to split URL testing.

Who it’s for

Cross-domain tests matter most to teams whose conversion happens on a different domain from the page they want to test:

• Ecommerce managers: test a delivery promise on product pages and judge it on orders completed on the separate checkout domain.
• Growth marketers: test a pricing page headline on the marketing site and count trial sign-ups completed in the app.
• CRO and experimentation leads: run one test across country domains and read a single report instead of several.
• Product managers: check that a change to the marketing site leads to more activated accounts as well as more clicks on Sign up.

By industry

The same set-up fits different journeys:

• Online stores: a store on one domain and its checkout or payment page on another, with the paid order as the goal.
• SaaS: a marketing site and an app on separate domains, with the completed sign-up in the app as the goal.
• Education: a course catalogue on one domain that sends enrolments to a learning platform on another, judged on completed enrolments.
• Lead generation: landing pages on a campaign domain that send visitors to a form on the main site.

How to start in Cuttl

In app.cuttl.io, add your second domain as a site in the same workspace and install the Cuttl Tag there. Then open Web Experiments, choose A/B settings, tick the site under Cross-domain tests, and create a test whose primary goal happens on that site. The Web Experiments page shows the test types and reports.

Cross-domain tests only follow clicked links, not form posts, script redirects or addresses typed into the browser. A visitor’s own user ID is never put in the link, and the link’s parameter is removed from the address bar when the page opens. If a visitor clears their browser storage on the first site, they come back there as a new visitor, and erasing a visitor also removes their cross-domain link.

Cross-domain tracking and tests are on the Max plan. AI assistants connected through the Cuttl MCP server can read a test’s results, including conversions on linked sites. You link the sites in the dashboard.

Common questions