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Optimizely pixel vs Google Pagespeed Insights

Basdeknegt 05-11-15

Optimizely pixel vs Google Pagespeed Insights




We use Optimizely as a tool for clients to optimize the conversion.
In Google Pagespeed Insights I see that the Optimizely pixel influence the pagespeed of the pages with Optimizely heavily.

Without Optimizely: 89/100
With Optimizely: 66/100

Of a SEO point of view this can influence the organic rankings heavily.
Could you please elaborate how we should solve this problem?

Thank you in advance for your support.

Ehsan 05-11-15

Re: Optimizely pixel vs Google Pagespeed Insights

Hi @Basdeknegt


We work with the largest CDN providers in the world to ensure that our snippet loads as quickly as possible.  When I visited for example, the Optimizley snippet loaded within 10-12ms (the jQuery on the page took 300-400ms).


By design, Optimizely will add milliseconds to your page load time, which will impact your pagespeed score.  While you can reduce this further by switching to asynchronous loading, we do not recommend this alternative as it will increase the changes of your visitors experiencing variation flashing.


You may be able to gain a few milliseconds by excluding the trimmed jQuery that loads with our snippet by default.  This setting can be changed in the Javascript section of the Settings tab in your Home Page.  However, you would need to move the jQuery script before the Optimizely snippet, which may not be beneficial in this case since it takes much longer to load.


Please see attached screenshots comparing the load time of Optimizely versus jQuery, and let me know if you have any follow up questions!




Basdeknegt 05-12-15

Re: Optimizely pixel vs Google Pagespeed Insights

Thanks for your reply Ehsan.


Good to know that, by design, Optimizely will impact our pagespeed scores. We've seen that, due to these changes in pagespeed score, our organic rankings have been decreased.


Could it be an alternative that we only fire the Optimizely snippet on pages that we are actualy testing? 





MartijnSch 05-12-15

Re: Optimizely pixel vs Google Pagespeed Insights

Hi Bas,


Are you absolutely sure that the load time is causing your issues. Your load times usually need to be absolutely dramatic to see any changes in your search traffic or rankings.

Ehsan 05-12-15

Re: Optimizely pixel vs Google Pagespeed Insights

Hi @Basdeknegt,


Yes, that works too!  The snippet only needs to be on pages that you are targeting and on pages where you are capturing goals.


Re: Optimizely pixel vs Google Pagespeed Insights

[ Edited ]

We recently shared some of the same concerns that Google would ding us in rankings because they claimed Optimizely was increasing pageload times. We conducted some testing on Optimizely's pageload impact and determined that it was negligible. But what if Google didn't acknowledge actual impact and only presumed it to be a degrading factor?


I think only putting Optimizely code on pages that are being actively tested is a great idea, just a pain to maintain without doing so via a tag manager (which results in an inferior test environment and is essentially the same as using the async Optimizely installation).


I also came across this bit of research not too long ago which suggests that "crawl time" and not "pageload time" is what correlates with page ranking. Personally, I think that leaves a lot unanswered such as exactly how the two metrics differ and how to measure the former effectively. This recent article from searchenglineland also confirms that Google does crawl javascript. I don't know if that's always been the case and if it calls for new research on crawl time vs pageload time impacting page rank.


Any way you look at it, it's a tricky spot to be in when it comes to optimizing conversions while optimizing for search engines. Great topic for discussion.

Basdeknegt 05-18-15

Re: Optimizely pixel vs Google Pagespeed Insights

Hi Martijn,

There are a lot of ranking factors so we are not 100% sure that the Optimizely snippet is fully responsible for our drop in rankings. However we've still seen a major drop in our pagespeed scores within the pagespeed insights tool from Google.

We will do a new test in de pagespeed insights tool with en without the Optimizely pixel implementend and we will share the results here.

Re: Optimizely pixel vs Google Pagespeed Insights

It does not impact on the pageload itself, but it does impact a lot the rendering time - especially on mobile devices - since blocking resources "above the fold" will cause the rendering process to stop and wait for the resource.


Also, the JS resource itself cannot be cached for more than 2 minutes, which make this problem persistent, on every page and along the whole user's session.


On the other hand, including the file in your page footer will most likely cause glitches.


I am not sure there is any real solution to this problem, besides disabling Optimizely whenever you don't really need it (i.e. when no experiment is active), although it makes the whole A/B testing process a bit more painful, and your mobile UX very unstable.



Basdeknegt 06-01-15

Re: Optimizely pixel vs Google Pagespeed Insights


Hey Guys, 


Attached the results of our page speed scores with en without the Optimizely snippet implemented. I'm wondering if this effect is ever discussed with Google?



Basdeknegt 06-12-15

Re: Optimizely pixel vs Google Pagespeed Insights

Hi Guys, 


I'm wondering if you can give us an update about the pagespeed issues based upon our test  results?