Mobile-first indexing
Google's practice of crawling, indexing and ranking based on the mobile version of a page; completed for all sites by mid-2024.
Technical
Viewport meta tag
The `<meta name="viewport">` declaration that tells mobile browsers how to size and scale a page to the device screen.
In full
`width=device-width, initial-scale=1` is the standard value; without it mobile browsers render at a default desktop width and zoom out, producing unreadable text and failing mobile usability checks. Setting `user-scalable=no` or a `maximum-scale` below 5 harms accessibility and is flagged by auditing tools. The viewport also defines what counts as 'in the viewport' for LCP and CLS measurement.
Example
A legacy print stylesheet template ships without a viewport tag, so mobile users see a 980 px-wide layout scaled down to illegibility.
Related terms
Responsive web design
Serving the same HTML at one URL and adapting layout with CSS media queries and flexible units, Google's recommended mobile configuration.
Cumulative Layout Shift
A Core Web Vital scoring unexpected visual movement of page content, computed from the largest burst of layout shifts; good is 0.1 or less…
Lighthouse
An open-source automated auditing tool in Chrome DevTools and PageSpeed Insights that runs lab tests for performance, accessibility, best…
Largest Contentful Paint
A Core Web Vital measuring the render time of the largest image, video poster or text block visible in the viewport; good is 2.5 s or less…