Mobile devices are being widely used to access the web today, and webmasters are required to ensure that their websites are catering well to mobile devices just as they do for desktop devices. This means that websites may require some optimization in order to best serve mobile web browsers. In response to various questions asked by webmasters in regards to same, Google has explained the current web experience using mobile phones and how to make your website mobile friendly in a Webmaster Central blog post.
According to the post, comparing the efficiency of a desktop web browser and a mobile phone web browser will help in understanding mobile phones and mobile friendly websites better. Mobile phones can be categorized in to – traditional mobile phones and smartphones.
Traditional mobile phones' browsers, like the ones for cHTML (iMode), WML, WAP etc., are incapable of displaying normal webpages that are designed for desktop browsers. While smartphones including Windows Phone 7, Blackberry devices, iPhones, Android phones and so on, has browsers that display normal webpages (tablets and eBook readers etc., also has the same browser). Smartphones can also be further categorized in to two, based on their HTML5 support – devices with browsers that do not support HTML5 and devices with browsers that support HTML5.
Smartphones and other mobile devices with browsers that display normal webpages has definitely changed the way mobile phones connect to the web, improving mobile web experience. However, with the constant development and improved versions of smartphones being manufactured, any current evaluation or classification (as in above) could change from time to time.
Google's crawlers and mobile content
Google has two crawlers – Googlebot (browser for desktop that crawls normal webpages) and Googlebot-Mobile (browser that crawls mobile content). The best way to serve your website's content to Googlebot-Mobile would be to understand the User-agent string type(s) that Googlebot-Mobile supplies when crawling your site. All User-agent strings used by Googlebot-Mobile uses the format – [Phone name(s)] (compatible; Googlebot-Mobile/2.1; +http://www.google.com/bot.html)
Therefore by finding out which of your site's content best serves the phone(s) in the User-agent string, you can decide which content to serve to Googlebot-Mobile and eventually provide better access to mobile devices. You can get a full list of Googlebot-Mobile User-agents here.
At present, Google does not crawl with Googlebot-Mobile using a smartphone User-agent string, therefore, “a correctly-configured content serving system will serve Googlebot-Mobile content only for the traditional phones described above” (as for now). If this, and it might, changes in future there will be a new Googlebot-Mobile User-agent string as well. Currently, smartphones deliver normal or desktop web experience for users, so webmasters require to perform no mobile-specific optimization on their sites. Still, some websites may serve in a better way if the content are formatted differently for smartphones.
Serving mobile content from the right URL
Many websites today has only one version of their content, which may not be serving traditional mobile phones. Also, the browsing experience of smartphone users will depend on the type of browser the smartphone has. If your site functions similarly, with only one version of the content, you should do the same for Googlebot-Mobile too. This is to say that you should treat Googlebot-Mobile like all other or unknown User Agents. If done so, “Google may modify your webpages for an improved mobile experience.”
However, if your site is optimized for mobile devices, “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.).” Also, as long as your site's URL structure returns exactly what a user sees, it does not matter matter what the URL structure is to Googlebot and Googlebot-Mobile. For instance, let's assume that you have URL structures like www.example.com and m.example.com and that you redirect mobile users from www.example.com to m.example.com. In such a case, both your URL structures will be recognized by Googlebot-Mobile and both the sites will be crawled and added to the correct index. Here, you should use a 301 redirect for both users and Googlebot-Mobile.
The important point to focus on is that you detect the User-agent correctly, just as it is given by your users and Googlebot-Mobile, then serve the same content to both. You should also store a default content (the desktop-optimized one), so you can use it anytime when an unknown user requests it. Plus, while using the Mobile Sitemaps feature in the Google Webmaster Tools, only mobile content URLs should be included (in the Mobile Sitemaps).
For any further information, you may visit Google's Mobile Sitemaps Help Center articles or download the Search Engine Optimization Starter Guide. You can also ask any related questions at the thread created in Help forum.