In 2023, Google completed mobile-first indexing for all sites, meaning the mobile version of every page is the primary basis for ranking — even for searches made on desktop. A site that works well on desktop but poorly on mobile is ranked based on the poor mobile version.
What Google Checks
Text Readability
Text should be readable without zooming. The general guideline is a base font size of at least 16px for body text. Text that's 10px small on mobile and requires pinching to read is a common failure.
Tap Target Sizes
Buttons and links should be large enough to tap accurately with a finger. Google's guideline is tap targets of at least 48×48 pixels, with sufficient space between them. Small, closely spaced links are a frequent mobile usability issue.
Viewport Configuration
The page must have a viewport meta tag telling the browser to scale the page to the device width: ``html <meta name="viewport" content="width=device-width, initial-scale=1"> `` Without this, a mobile browser renders the desktop version of the page at full scale, requiring zoom to read.
No Horizontal Scrolling
Content should fit within the device width. Images wider than the screen, fixed-width layouts, or overflowing text cause horizontal scrolling, which is a significant usability problem on mobile.
Interstitials and Pop-ups
Large pop-ups that cover the content immediately when a user lands on the page from search are a specific Google mobile guideline issue. Small cookie notices and easily dismissible banners are fine; full-screen interstitials that block content are not.
Checking Your Site
Use SEO Checker for on-page basics, and Google's Mobile-Friendly Test for a direct mobile assessment. Google Search Console's Mobile Usability report shows issues found across the whole site with specific affected URLs.
The Practical Priority
For most sites using a modern CMS on a responsive theme, mobile-friendliness is handled at the template level. The most common specific issues are:
- Font sizes set too small in custom CSS.
- Buttons or links too small or too close.
- Images without
max-width: 100%that overflow on small screens. - Fixed-width containers that don't adapt.
For broader page speed issues that also affect mobile, see what is page speed and why does it matter for SEO.
Mobile-First Indexing in Practice
Mobile-first indexing means if your desktop site has comprehensive content but your mobile site hides some of it (a common pattern with older "mobile themes"), Google's index only sees the mobile version's content. This affects what can rank. Check both versions of your key pages side by side to confirm the same content, headings and structured data appear in both. For checking broader technical health across a page at once, run through SEO Checker. For the speed component of mobile experience — which often matters more than layout alone — see what is page speed and why does it matter for SEO and core web vitals explained in plain English.
