Webmaster level: Intermediate
We’ve noticed a rise in the number of questions from webmasters about how best to structure a website for mobile phones and how websites can best interact with Googlebot-Mobile. In this post we’ll explain the current situation and give you specific recommendations you can implement now.

Some Background

Let’s start with a simple question: what do we mean by “mobile phone” when talking about mobile-friendly websites?
A good way to answer this question is to think about the capabilities of the mobile phone’s web browser, especially in relation to the capabilities of modern desktop browsers. To simplify matters, we can break mobile phones into a few classifications:
  1. Traditional mobile phones: Phones with browsers that cannot render normal desktop webpages. This includes browsers for cHTML (iMode), WML, WAP, and the like.
  2. Smartphones: Phones with browsers that render normal desktop pages, at least to some extent. This category includes a diversity of devices, such Windows Phone 7, Blackberry devices, iPhones, and Android phones, and also tablets and eBook readers.We can further break down this category by support for HTML5:
    • Devices with browsers that do not support HTML5
    • Devices with browsers that support HTML5
Once upon a time, mobile phones connected to the Internet using browsers with limited rendering capabilities; but this is clearly a changing situation with the fast rise of smartphones which have browsers that rival the full desktop experience. As such, it’s important to note that the distinction we are making here is based on the current situation as we see it and might change in the future.

Googlebot and Mobile Content

Google has two crawlers relevant to this topic: Googlebot and Googlebot-Mobile. Googlebot crawls desktop-browser type of webpages and content embedded in them and Googlebot-Mobile crawls mobile content. The questions we’re seeing more of can be summed up as follows:
Given the diversity of capabilities of mobile web browsers, what kind of content should I serve to Googlebot-Mobile?
The answer lies in the User-agent that Googlebot-Mobile supplies when crawling. There are several User-agent strings in use by Googlebot-Mobile, all of which use this format:
[Phone name(s)] (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)
To decide which content to serve, assess which content your website has that best serves the phone(s) in the User-agent string. A full list of Googlebot-Mobile User-agents can be found here.
Notice that we currently do not crawl with Googlebot-Mobile using a smartphone User-agent string. Thus at the current time, a correctly-configured content serving system will serve Googlebot-Mobile content only for the traditional phones described above, because that’s what the User-agent strings in use today dictate. This may change in the future, and if so, it may mean there would be a new Googlebot-Mobile User-agent string.
For now, we expect smartphones to handle desktop experience content so there is no real need for mobile-specific effort from webmasters. However, for many websites it may still make sense for the content to be formatted differently for smartphones, and the decision to do so should be based on how you can best serve your users.

URL Structure for Mobile Content

The next set of questions ask about the URLs mobile content should be served from. Let’s look in detail at some common use cases.

Websites with only Desktop Experience Content

Most websites currently have only one version of their content, namely in HTML that is designed for desktop web browsers. This means all browsers access the content from the same URL.
These websites may not be serving traditional mobile phone users. The quality experienced by their smartphone users depends on the mobile browser they are using and it could be as good as browsing from the desktop.
If you serve only desktop experience content for all User Agents, you should do so for Googlebot-Mobile too; that is, treat Googlebot-Mobile as you treat all other or unknown User Agents. In these cases, Google may modify your webpages for an improved mobile experience.

Websites with Dedicated Mobile Content

Many websites have content specifically optimized for mobile users. The content could be simply reformatted for the typically smaller mobile displays, or it could be in a different format (e.g., served using WAP, etc.).
A very common question we see is: Does it matter if the different types of content are served from the same URL or from different URLs? For example, some websites have www.example.com as the URL desktop browsers are meant to access and have m.example.com or wap.example.com for the different mobile devices. Other websites serve all types of content from just one URL structure like www.example.com.
For Googlebot and Googlebot-Mobile, it does not matter what the URL structure is as long as it returns exactly what a user sees too. For example, if you redirect mobile users from www.example.com to m.example.com, that will be recognized by Googlebot-Mobile and both websites will be crawled and added to the correct index. In this case, use a 301 redirect for both users and Googlebot-Mobile.
If you serve all types of content from www.example.com, i.e. serving desktop-optimized content or mobile-optimized content from the same URL depending on the User-agent, this will also lead to correct crawling by Googlebot and Googlebot-Mobile. This is not considered cloaking by Google.
It is worth repeating that regardless of URL structure, you must correctly detect the User-agent as given by your users and Googlebot-Mobile, and serve both the same content. Don’t forget to keep the default content, the desktop-optimized content, for when an unknown User-agent requests it.

Mobile Sitemaps in Webmaster Tools

Finally, we receive many questions about what URLs to put in Mobile Sitemaps. As explained in our Mobile Sitemaps Help Center articles, you should include only mobile content URLs in Mobile Sitemaps, even if these URLs also return non-mobile content when accessed by a non-mobile User-agent.

More Questions?

A good place to start is our Mobile Sites Help Center articles and the relevant sections in our Search Engine Optimization Starter Guide. We also created a thread in our forums for you to ask questions about this post.