There's quite the debate between using a single-domain or an m-dot URL to deliver a mobile site. And in a world where SEO is so important, it has - of course - crept into the conversation.

Here at Moovweb, we don’t have a dog in the fight. Our platform supports either using a single-URL or an m-dot to deliver a mobile-optimized page. And we’ve seen both used well, which puts us in an interesting situation to evaluate their merits.

Before we get too deep into the it, let's skip to the end: You can use mobile-optimized pages that have different URLs. You just can. Whether it’s an m-dot, or any other URL. Ignore the FUD.

And here's why:

Good SEO is about making quality sites with pages that search engines can correctly crawl and read. Google wants you to make your site easy for them to index. And when you’re relying on them sending visitors your way, you have every reason to oblige them.

But Google is also full of some pretty smart people, and they aren’t flummoxed by simple matters like two versions of a page.

If you don’t believe me, read the Google Developer "Building Smartphone-Optimized Websites" documentation.

"A common setup would be pages on www.example.com serving desktop users having corresponding m.example.com pages serving mobile users. Google does not favor any particular URL format as long as they are all accessible to both Googlebot and Googlebot-Mobile."

If you don’t feel like reading that, just login to GMail on your mobile browser. Next try Google News. Then YouTube. Each is a Google property. Each uses mobile-specific URLs. There’s really no doubt about it. Google has no problems with m-dot sites.

Why? Because they can easily connect the two versions of the page with each other. All you have to do is put this in the desktop page's head:

<link href="http://m.example.com/page-1" rel="alternate" media="only screen and (max-width: 640px)" />

And then put this in the mobile page's head:

<link rel="canonical" href="http://www.example.com/page-1">

That’s it. Google now knows when it crawls the separate URLs that they are actually two experiences of the same page, and treats them as one.

Alright, that’s done. Good? Good. Now let’s take it back to see how and why we got here.

The Early Days

Since developers decided to create the first mobile-optimized sites they’ve been debating how to manage the separate experience. And it hasn’t always been pretty. Remember .mobi?

In late 2006 a few large websites jumped on the idea of having their mobile optimized site live on a completely different top-level domain. If you wanted to visit ESPN from your computer, you went to the familiar www.ESPN.com. But from your mobile device you went to www.espn.mobi.

Yeah. That wasn’t going to work, for oh so many reasons. Like that it required sites to secure a new domain name that matched their ".com", that required users to use a different , and that ".mobi" already existed as a file extension for ebooks.

But the web quickly figured . We settled around the idea of using sub-domains, which had the flexibility of not requiring owning multiple top-level domains. So you went to www.ESPN.com on your laptop, and m.ESPN.com on your phone. Much more reasonable.

Redirection and Dynamic Serving

Delivering mobile became even better with device detection and re-direction. Now there was no need to even type in the m-dot. For the first time you basically had one URL. Visit www.twitter.com from whatever you’re using – and if it’s a mobile device you are automatically redirected to “mobile.twitter.com”. Simple, easy.

Along with that is is dynamically served HTML. It takes the similar philosophy, but instead of housing the different experiences on different linked pages, the server just returns one or the other to the same URL. An example of this is Amazon. Go to Amazon.com on your laptop and your mobile device. Both will show the "Amazon.com" URL, but the HTML for each will be different.

Okay, so why the m-dot SEO fear?

If your company runs from search engines traffic, it’s completely rational to be fearful of bad SEO practices. Whole sites have been crippled after black hat and general bad SEO practices caught up to them. Mix that healthy respect of SEO with a changing medium and quite a bit of uncertainty, and it’s not hard to see how some get down on m-dots.

And if your looking for the cause of that uncertainty, look no further than the fear of “duplicated content”. If you care about SEO, you have be weary of duplicated content.

Google Panda, an update in early 2011 to the Google search algorithm, threw down the gauntlet on sites with “thin, low quality, and duplicate content.” This meant that if you were re-using content, you felt the sting of a Google penalty – less traffic to your site.

This is when many eCommerce sites really started paying attention to original content. For years they had, along with all their competitors, been using product descriptions provided by the manufacturer. But now they could write an original description and leapfrog the competition in the Google rankings.

Suddenly duplicated content was the SEO kiss of death, and in some weird and wrong-headed way m-dot sites got associated with it.

Making the call

Between these two modern solutions, either using an m dot or a single-url, there are inherent up-sides and down-sides for both.

If you’re working on mobile specific campaigns, an m-dot site could be an imperative. That said, for a content site that sees a significant amount of traffic from link sharing, a single URL might be the way to go. It can frustrate users when they open up a link shared from mobile on their laptop and they get the mobile experience.

There's nuance to the decision, and it depends on the site and how it is used. So you can put up an argument for either, but one of them being “bad for SEO” just isn’t one of those reasons.