Minimize A/B testing impact in Google Search

This page covers how to ensure that testing variations in page content or page URLs has minimal impact on your Google Search performance. It does not give instructions on how to build or design tests, but you can find more resources about testing at the end of this page.

Overview of testing

Website testing is when you try out different versions of your website (or a part of your website) and collect data about how users react to each version.

  • A/B testing is where you test two (or more) variations of a change. For example, you may test different fonts on a button to see if you can increase button clicks.
  • Multivariate testing is where you test more than one type of change at a time, looking for the impact of each change as well as potential synergies between the changes. For example, you might try several fonts for a button, but also try changing (and not changing) the font of the rest of the page at the same time. Is a new font easier to read and so should be used everywhere? Or is the benefit that the button font looks different to the rest of the page, helping it draw attention?

You can use software to compare behavior with different variations of your pages (parts of a page, entire pages, or entire multi-page flows), and track which version is most effective with your users.

You can run tests by creating multiple versions of a page, each with its own URL. When users try to access the original URL, you redirect some of them to each of the variation URLs and then compare users' behavior to see which page is most effective.

You can also run tests without changing the URL by inserting variations dynamically on the page. You can use JavaScript to decide which variation to display.

Depending on what types of content you're testing, it may not even matter much if Google crawls or indexes some of your content variations while you're testing. Small changes, such as the size, color, or placement of a button or image, or the text of your "call to action" ("Add to cart" vs. "Buy now!"), can have a surprising impact on users' interactions with your page, but often have little or no impact on that page's search result snippet or ranking.

In addition, if we crawl your site often enough to detect and index your experiment, we'll probably index the eventual updates you make to your site fairly quickly after you've concluded the experiment.

Best practices when testing

Here is a list of best practices to avoid any bad effects on your Google Search behavior while testing site variations:

Don't cloak your test pages

Don't show one set of URLs to Googlebot, and a different set to humans. This is called cloaking, and is against our spam policies, whether you're running a test or not. Remember that infringing our spam policies can get your site demoted or removed from Google search results—probably not the desired outcome of your test.

Cloaking counts whether you do it by server logic or by robots.txt, or any other method. Instead, use links or redirects as described next.

If you're using cookies to control the test, keep in mind that Googlebot generally doesn't support cookies. This means it will only see the content version that's accessible to users with browsers that don't accept cookies.

If you're running a test with multiple URLs, you can use the rel="canonical" link attribute on all of your alternate URLs to indicate that the original URL is the preferred version. We recommend using rel="canonical" rather than a noindex meta tag because it more closely matches your intent in this situation. For instance, if you are testing variations of your home page, you don't want search engines not to index your home page; you just want them to understand that all the test URLs are close duplicates or variations on the original URL and should be grouped together, with the original URL as the canonical. Using noindex rather than rel="canonical" in such a situation can sometimes have unexpected bad effects.

Use 302 redirects, not 301 redirects

If you're running a test that redirects users from the original URL to a variation URL, use a 302 (temporary) redirect, not a 301 (permanent) redirect. This tells search engines that this redirect is temporary—it will only be in place as long as you're running the experiment— and that they should keep the original URL in their index rather than replacing it with the target of the redirect (the test page). JavaScript-based redirects are also fine.

Run the experiment only as long as necessary

The amount of time required for a reliable test will vary depending on factors like your conversion rates, and how much traffic your website gets; a good testing tool tells you when you've gathered enough data to draw a reliable conclusion. Once you've concluded the test, update your site with the desired content variation(s) and remove all elements of the test as soon as possible, such as alternate URLs or testing scripts and markup. If we discover a site running an experiment for an unnecessarily long time, we may interpret this as an attempt to deceive search engines and take action accordingly. This is especially true if you're serving one content variant to a large percentage of your users.

More information about testing