Definition
Mobile-first indexing: definition and effects
Mobile-first indexing is the way Google crawls and indexes a site from its mobile version. Its crawler presents itself as a smartphone, and the content it sees at that moment is what serves for indexing and ranking, whatever device the person searching uses. Google keeps only one index.
One index, built on the mobile version
There is no index for phones and another for computers. Since Google completed the move to mobile-first indexing, its single index is built from what the crawler encounters while presenting itself as a phone. The underlying ranking is therefore the same for everyone.
The consequence is direct: content missing from the mobile version counts for nothing, on any device. Google recommends that both versions show the same content (text, images, videos and links), as well as the same metadata and structured data.
Where the gaps hide
Gaps rarely come from a decision. They come from a theme that removes blocks below a certain screen width, a menu that no longer exposes some links, a table taken off the mobile display because it overflowed, or a section loaded only after a visitor action.
The distinction that matters is between collapsing and removing. A collapsed block (one that opens on tap) stays in the code and counts for ranking. A block removed from the code below a certain width disappears for Google, even on desktop.
What it does not explain
Different rankings on a phone and a computer do not prove an indexing problem. They usually come from display and context: a phone screen shows fewer results, and local results take up more room on it. The same position therefore does not bring the same number of clicks.
A manufacturer publishes a compatibility table on every product page. To keep it from overflowing on phones, its theme removes it from the code below 768 pixels wide. Google's crawler, which presents itself as a phone, never sees the table: the compatible models listed in it do not help the page rank on any device, desktop included.
Collapsing the table into a block that opens on tap keeps it in the code. Content already paid for goes back to work.
We read mobile-first indexing as a budget question before seeing it as a technical one. Everything written that does not appear on a phone is paid content that produces no ranking. A gap between mobile and desktop is therefore almost never a ranking problem: it is a problem of content nobody sees.
Deciding what must appear on mobile remains a business decision: only the company knows which table or detail answers its customers' main objection.
Not to be confused with
- Responsive site
- A responsive site serves the same code at the same URL and adjusts the display to the screen. It is the build approach Google recommends, but it does not guarantee parity: a responsive theme can still remove blocks from the code.
- Separate mobile index
- It does not exist. Google keeps a single index, and ranking gaps between devices come from display and search context.
Related concepts
Further reading
- Mobile vs. desktop SEO: why your Google rankings differ
- Technical SEO: finding crawl and indexing problems
- Google Business Profile: how to improve your local visibility
- Website redesign: defining goals before you begin
- Website design for visitors, search engines and AI
Related services
Frequently asked questions
My site is responsive: am I covered?
Not automatically. A responsive theme can remove blocks from the code below a certain screen width. Compare the code rendered by Google with your page as it appears on desktop.
How can I see what Google sees on mobile?
The URL Inspection tool in Search Console shows the code Google rendered when it crawled the page. Any gap in text, links or tags compared with your page is a ranking gap.
