Bing had earlier talked about it in May 2015 when they announced about their Mobile Friendly Algorithm.
Bing uses following criteria to determine the mobile friendly nature of a web page:
- Viewport and Zoom control configuration
- Width of page content
- Readability of text on the page
- Spacing of links and other elements on the page
- Use of incompatible plug-ins
The tool also checks for and reports the resources needed to analyze the page but weren’t crawled due to robots.txt constraints.
If a page fails to satisfy any criteria, detailed information on the failure is provided.
Bing Releases Mobile Friendliness Test Tool!,