# Mobile-First Indexing — SEO for Developers: Technical SEO and Core Web Vitals
Source: https://www.skillbyai.com/en/seo-developers/seo-mobile-first
> Understand that Google now indexes the mobile version of your site first and evaluates it for ranking.
## Mobile-first is the default
Google now uses the *mobile* version of every site for indexing. If your mobile page is slower, hides content or has poor UX, rankings can suffer regardless of how good the desktop page is.
## Responsive design example
Use responsive CSS to make your site work on all screen sizes. Use the viewport meta tag and CSS media queries.
```html
Mobile-Friendly Content
```