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Impact of A/B testing on Search Engine Optimization (SEO)

Update: there is even an official confirmation from Google’s Matt Cutts that split testing does not impact search rankings.

A lot of our potential customers are concerned whether A/B or multivariate testing will have an effect on their search engine rankings. They (obviously) aren’t looking to improve their rankings by using A/B testing, rather their concerns relate to the myth that testing may negatively impact search engine optimization efforts.

Broadly, there mainly two major concerns:

  • Content Cloaking: the act of showing different content to search engine bots and actual human visitors. A/B testing software (such as Visual Website Optimizer) swap content on the page using JavaScript, so some users see different content (of variations) and bots see original page only.
  • Duplicate Content: the act of copying content from elsewhere and hosting it on your site. Search engines penalize for such stealing of content because you cannot expect to rank on keywords for the content that isn’t yours. Again, many A/B and multivariate testing software (including VWO) have an option where you can redirect site traffic to different variations of a page which raises this concern.

Why A/B testing is not content cloaking

Cloaking content was all rage back in the early days of search engines (think 1990s). In those days, SEO was all about keyword stuffing. So, smart SEO geeks used to display a page full of keywords when a search engine bot visited to crawl / index the page. While if a user visited the same page, they displayed the default (normal) version. This strategy of keyword stuffing used to work like wonders so naturally search engines started devising clever ways to detect and penalize such cloaking and it may appear that pages where A/B testing is on will also get penalized because it is kind of cloaking.

Good news is that thanks to Google’s PageRank algorithm, keyword stuffing no longer works. So, there is little incentive for search engines to penalize content cloaking. Moreover, unlike yesteryears’ static HTML sites, today’s search engines have come to expect highly dynamic AJAX driven sites. So, they no longer consider swapping content dynamically as cloaking. If you use a multivariate testing software to swap different parts of your page, it is not cloaking! Also, all the major search engines (Google, Yahoo, Bing, etc.) are well versed with concept of A/B split testing and they do many such tests on their own sites every single day. You wouldn’t expect search engines to penalize others for doing the same activity that they themselves do regularly, would you?

Key lesson: Doing A/B testing by dynamically swapping elements on page (using JavaScript) is NOT content cloaking. It is absolutely safe and should not have any negative impact on Search Engine Optimization efforts.

Split URL testing (redirecting traffic to multiple versions) and the issue of content duplication

As I mentioned above, this is another issue that worries many prospective customers. While one approach for split testing is to dynamically swap page elements (such as headlines, images, text, etc.), another approach is to host different variations of page on your website. So, if you want to split test product.html, you will create variation pages and host them as product1.html, product2.html, etc. A split testing software will redirect all traffic coming to product.html to the variation pages. Since product1.html and product2.html will have similar content as product.html, it worries some people that search engines will consider them duplicate content and penalize rankings.

An important point to note here is that search engines only penalize if you steal or host content from a different domain; here all variations pages host on your own site and you OWN that content and are free to do with it whatever you want to. Many dynamic websites (shopping carts, directories, etc.) today host the same content in different formats. Search engines don’t penalize them because that unique content is only found on their domain and no where else. Same is the case with your split testing URLs. You don’t get negatively impacted by it because you haven’t stolen that content — it is all yours!

If you are worried about the SEO ranking of the control page, it is possible to setup a Split URL test in a manner so that you can avoid the issue of duplicate content by using the following on your variation version URL:
Let me explain this with the help of a example below:
A Split URL test is when there are two pages (let’s say and and when visitors land on, half of them are redirected to with some duplicate content on it. In this case, let’s suppose you don’t want B.php to affect your SEO, so what you do is add the following code to B.php i.e. the non-canonical page
<link rel=”canonical”/>
Now Google will index both pages but it will know that is the one to be used for SEO purposes. Here’s the link to the help page from Google’s own website.

Lesson: A/B split testing has absolutely NO negative impact on your SEO efforts!

Rest assured, you can use Visual Website Optimizer without worrying about its impact on search engine rankings. If you have a specific SEO and A/B testing related question, let me know in comments below.

UPDATE: Things have changed since this article was written. Please see for Google’s guidelines on A/B testing.

Founder and Chairman of Wingify.

Comments (21)

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  1. “Your variation pages can only be reached if there is a link pointing to it. Since you don’t link to your variation pages from anywhere from the site or else-where, search engines won’t know that those pages even exist.”

    Wrong. Search engines, and Google in particular, will do anything they can to find new content and will not rely only on skipping from link to link to find it. This includes, but not limited to, gathering data from toolbar users, Chrome users, etc.

    Another thing that is important to add in the A/B testing context is that if different versions of your test have varying URLs, the chances are that you will receive links to both versions. Once you end the test, the links to the temporary pages may be lost, so it is important to 301 all the test URLs to the final, live URL of that page and thus combine the link equity

    1. @Branko: good point about 301 redirect. Yes, that’s what we recommend to the users once they finish the test.

      It is interesting that they will gather the URL data from Chrome or Toolbar. Are you sure about that?

  2. I was delaying A/B testing because I worried that the only way to do this without impacting PR was through Google’s Site Mastertools… which are not as good as some of the paid tools.

    Your article is a huge stress reliever. Many thanks.

  3. Well articulated points about concerns that I’ve heard internally (I work for an SEO service provider) and have been trying to address lately. Thanks!

  4. Duplicate content concerns: I think the Nofollow is the best advice… My understanding is you can own all the content you have, yet if you keep using it (over and over: duplicate content), the first 2 versions of it might get indexed and the next X versions will not. A big bummer if the “next version” is the “real version”.

  5. Hi Lars,

    I like the post here (as well as the dialogue reminder on 301s). But I think customers should keep in mind that many A/B test focus on elements on a page — if different location for images, varying images, and tweaks to content – make a difference, and is short term compared to what search engines typically look for. Your comments are spot on – I just think that there can be such an overfocus on the SERP that firms forget that A/B is a tool that verifies how to best enhance the customer experience online, which really is more important to the goal of the site.

  6. “It is interesting that they will gather the URL data from Chrome or Toolbar. Are you sure about that?”

    Yes. It was shown in many cases, I have personally seen unlinked pages being indexed only after visits with toolbar or chrome. The most recent example i remember is the following quote in Google’s “Ranking documents based on user behavior and/or feature data” patent:

    “This user behavior data could be obtained from a web browser or a browser assistant program””

    Here is the patent covered by Bill Slawski

  7. You guys are right in many ways, but also critically wrong on a crucial factor. While the advice you gave may apply to small number of pages indexed, the advice you gave is totally and utterly irresponsible for enterprise SEO with millions of pages indexed.

    using javascript to shield dynamic content from the problem of maintaining internal link structure is a valid strategy and is a good use of VWO. However, any kind of system using multiple URLs is a dangerous and illogical in many many ways. I did write a response on my website if anyone cares to read it. Hopefully VWO will retract the section about multiple URLs.

  8. A good way of preventing the duplicate content issue from happening is to make sure you have rel=canonical tag in place, instructing search engiens that the ‘original’ is located at a certain place. Because these test pages are often a rearrangement of items this is definately a way to go and search engines respect in mose cases.

  9. Should we worry that page load speed could be negatively affected by adding the VWO test Javascript to the page? Especially if it does not load asynchronously or requires a redirect?

  10. Paras,

    I appreciate that you wrote the article in 2010 but I think that some of the statements you’ve made are a bit bold and need to be updated.

    Google recommends adding a rel=”canonical” to all variations pointing back to the original URL. They also don’t recommend the noindex option.

    You should also mention the use of 302 redirects as opposed to 301 redirects that can cause havoc.

    1. @Modesto: thanks for pitching in. Yep, rel=”canonical” is a great option for split URL testing. Do you have any link where they suggest noindex shouldn’t be used? It is quite likely that my advice could have gotten a little stale, so I would update article if there are any wrong facts.

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