As part of Bing's roadmap in making web searches more friendly to mobile users, the company has added "mobile-friendly" tags on searches to determine which sites will render better in mobile devices.

The update on the search engine, according to Bing's official blog post, received a positive feedback as users were able to "skim through the search results to know which ones will quickly answer their information needs."

Shyam Jayasankar of the Bing Mobile Relevance Team said mobile users prefer to open websites that are marked with the mobile-friendly tag without having to skim through one page of search result when browsing for information

To rate a website as mobile-friendly, the Bing Team rate it by its navigation experience, readability, scrolling and compatibility with mobile devices. 

Buttons, menus and links that are arranged to close to each other that causes accidental clicks destroy the mobile-friendly navigation experience in a website. Mobile users want "large, easy-to-tap and distinct navigational elements."

In terms of readability, the text or content displayed should be large enough but without the need to scroll laterally or to zoom in.

While scrolling vertically is acceptable for many mobile users, scrolling horizontally is not. The Bing Team said that the content of mobile-friendly sites usually fit in the screen of a device either on portrait or landscape mode. Horizontal scrolling

Compatibility with mobile devices is also an issue with many websites. Bing reported that web pages containing Flash content don't display properly with iOS devices. The same applies to video content that require plugin dependencies, copyright issues or distribution decisions by the content owner.

The factors mentioned are also what the Bing Team puts into their detection algorithms to measure the ranking a website's mobile-friendliness. To determine these features further, webmasters are advised to allow Bingbot mobile user agents.

They launched their mobile user agents in November last year for web designers and allow it to probe into their websites. It will download the necessary custom style sheets (CSS) and script files of a webpage in order for Bing to check its mobile-friendliness.

However, this doesn't mean that Bing would always give mobile-friendly websites in a search and may still suggest the most relevant result in each query. It also doesn't mean that they will penalize a website for not being mobile-friendly.

Bing started looking into mobile relevance and mobile friendliness when web searches done on mobile devices grew last year.