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I recently came across a site that had the following code: 

<link rel="dns-prefetch" href="//ajax.googleapis.com">

In looking it up it says it is used to Reduce DNS lookup time by pre-resolving at the browser.

So my question is, other than (hopefully) making the site feel a touch more faster, does it have any other impacts on SEO or the site in general?

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  • I learned something new today. Thanks! As far as SEO, I am sure it is minimal in that it effects page speed- meaning that if page speeds are within the okay realm and under normal conditions any reference resolves okay, then the effect would be fairly small, but if there are resources in the HTML code that resolve slower and slows the page speed enough to effect this ranking metric, then the result would be much larger. So it would depend on the resources and the DNS (users or SOA) and how well they resolve. It could be a case by case thing. Other than that, I have no idea as to effect.
    – closetnoc
    Commented Jun 19, 2014 at 4:24
  • Nice question (and new tag!). I never thought of that in terms of SEO, but faster is always a plus for users and bots alike. Maybe someone will have some experience on their results with using it.
    – dan ♦
    Commented Jun 19, 2014 at 5:41
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    Often I see dns-prefetch implemented on commonly used URLs anyway, so I am not sure how much value it has in general in terms of page performance as these domains are likely already in your DNS cache. If you had many unique DNS lookups required, I could see the utility.
    – jeffatrackaid
    Commented Jun 19, 2014 at 13:59
  • Got a feeling it gives a better score on pagespeed, which is a good thing.
    – Abu Nooh
    Commented Jun 20, 2014 at 0:48
  • CSS Tricks has an article on prefetching and more that helps explain some of this. Worth reading.
    – L84
    Commented Sep 3, 2015 at 21:01

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Google and other search engines ignore tags they don't recognize and directives that are not specifically geared towards search engines. As such there will be no direct impact on rankings. Search engines won't use dns-prefetch as a direct ranking signal.

There are indirect SEO benefits when your site is faster. Google does measure how users react to your website. Do they hit the back button because the site is too slow? If using dns-prefetch makes your site appear more quickly to users, then by all means use it. See: Why is loading speed of a website important for SEO?

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