Microsoft today announced Bing will start rolling out mobile friendliness ranking changes “in the coming months.” The company shared the news and laid out exactly how its search engine determines which webpages to label as “Mobile-friendly.”

The label lets users skim through mobile search results and quickly see which ones will load quickly and display properly. Unsurprisingly, Microsoft found visitors “strongly prefer” pages marked with the mobile-friendly tag as they can find the information they seek much faster.

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Using mobile friendliness as a ranking signal will only affect Bing’s mobile searches, and Microsoft promises “webpages that are highly relevant to the given query that are not yet mobile-friendly will not get penalized.” In a few weeks, the Bing team will release a tool to analyze webpages using its mobile-friendliness classifier to help webmasters find and fix mobile issues on their site.

In the meantime, here is a summary of the four factors that Bing’s classification algorithm uses to determine whether a webpage is mobile-friendly:

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  1. Navigation — The menus, buttons and links on the page should be large enough and spaced well apart to aid touch-based navigation.
  2. Readability — The text on the page should be readable without requiring zooming and lateral scrolling to access specific content. Keep in mind that readability is influenced both by font size and the viewport settings (defined in HTML tags).
  3. Scrolling — The content of the webpage should fit within the device width. Vertical scrolling is considered acceptable, but the need to scroll horizontally hampers the ability to consume your content easily. Well-designed mobile pages typically fit well to the device width in both portrait and landscape orientations.
  4. Compatibility — The content needs to be compatible with the device. This applies to videos that cannot be played on mobile devices due to plugin dependencies, copyright issues, or distribution decisions made by the content owner.

Microsoft says more factors are also taken into account, such as the friction that pop-ups sometimes create in navigating to the core content of the page. Webmasters should keep in mind that Bing can’t mark their site as mobile-friendly if it can’t access all the necessary CSS and script files required by your page.

Microsoft is quite behind in its mobile-friendly push; the company shared its plans in November and says Bing only recently started labeling sites as “Mobile-friendly.” In comparison, Google started labeling mobile-friendly sites in November and rolled out mobile ranking changes last month. Better late than never?