Google strongly implied to us that this will become a ranking factor. A Google spokesperson told us:
“Because at Google we are aiming to provide a great user experience on any device, we’re making a big push to ensure the search results we deliver reflect this principle. We want users to be able to enjoy the web wherever they are.”
If the mobile version of a website has tiny fonts, once GoogleBot renders the page, it can see that because it actually renders the page as a user would. For example, if the HTML has a 14px font size, then once rendered with JavaScript and CSS, it might have modified those to 8px instead. This on a tiny view-port could lead to a bad user experience.
Another example might be how a mobile site requires zooming and panning for a user to see the site. GoogleBot will correlate it to view-port of the mobile device and see how it impacts the user.
Why Is Mobile UX Important?
A Google spokesperson sent us this statement:
“Mobile-friendly websites provide a much better user experience for the mobile users. According to our studies, 61% of users are unlikely to return to a mobile site that they had trouble accessing from their phone. That includes sites that use fonts which are illegible on mobile, or sites where users have to zoom in or pan around excessively. Mobile is a very important area; the mobile device penetration is over 50% in the USA and most users use their device for browsing websites.”
