Mobile first means you design the phone version first and treat the desktop version as the variation. For a trade this is not a preference, it is arithmetic. The person with a leak is standing in the room with the leak, holding a phone, one handed, probably in a hurry.
Google looks at the phone version too
Google uses mobile first indexing, which means it primarily crawls and indexes the phone version of your pages. It set this out in its own documentation on mobile first indexing.
So if content is hidden on your phone version, or the phone version is a stripped down copy, that is the version being judged. A great desktop site with a thin mobile version is a thin site.
A worked example
A builder's site looked excellent on a laptop. On a phone the gallery ran off the side of the screen so the page slid sideways, the phone number only appeared in the desktop header, and the quote form's buttons sat too close together to tap accurately.
None of this was visible to the person who built it, because they built it on a desk. Ten minutes on an actual phone found all three.
Testing your own
Turn off the wifi so you are on mobile data. Load your site. Time how long until you can read something useful. Try to ring the firm without scrolling. Swipe sideways and see if the page moves, because it should not. Try the form with your thumb, not your fingertip. Everything you find in those two minutes is costing you work.
Why it matters for your site
Check these on your own site
- Open your own site on your own phone, on mobile data, and you will see what most of your customers see. Build for that screen first.
- Nothing should scroll sideways. A page that slides feels broken.
- The phone number must be tappable and reachable without scrolling.
- Buttons and form fields need to be thumb sized, with space between them.
- Do not hide content on mobile. Google indexes the phone version.
Common questions
What does mobile first mean for a website?
It means the phone layout is designed first and treated as the main version, with larger screens adapted from it, rather than the other way round.
Does Google use the mobile version of my site?
Yes. Google uses mobile first indexing, so it primarily crawls and indexes the phone version. Content hidden on mobile may not be counted.