What is the Mobile First Index?

As the use of mobile devices has been increasing for years a mobile optimized website is essential. Google has long since responded. With the Mobile First Index, Google uses information found on the mobile version of a website to compile search results.

What is the Mobile First Index

With the Mobile First Index, Google is taking account of the “mobile revolution” and will in future evaluate search results exclusively on the basis of the information found on the mobile version of a website.

Only the mobile version of a website is considered for the ranking.

The first announcement of this project came in November 2016. In April 2018, Google officially announced the introduction of mobile-first indexing, but also pointed out that not all websites would be converted directly to this new indexing method.

Background: How does a search engine work?

The goals of the Mobile First Index can be better understood by understanding how Google Search works. In their videos “How Search Works” and “How Google Works: A Google Ranking Engineer’s Story”, Matt Cutts and Paul Haar from Google succinctly summarize how a search query is served on Google:

How Search Works
How Google Works: A Google Ranking Engineer’s Story

More information about Google’s search can be found at https://www.google.com/search/howsearchworks/.

In simplified terms, three important components can be identified that takes a search and turned it into a search result.


Google’s web crawlers call up websites and index their content. These crawlers, also called spiders, behave like a browser when a website is called up, but without a graphical user interface. A website is called up, loaded and set up in the same way as with a “real” user.


Google’s index stores all information on all documents and their associated resources, links and structured data, to name but a few. It is the heart of the search engine; without this extensive storage space, Google would not be able to provide search results so quickly.

So that the search engine does not have to send a crawler “through the Internet” every time it searches, the information that the crawlers have collected is stored locally – in so-called shards. So there is not one database, but many parts that are distributed across different data centers.

Ranking factors

The ranking signals or factors, much discussed in SEO circles, are the brain of the search engine. These sets of rules put the websites that are suitable for a corresponding search in a meaningful order, which is based, among other things, on the relevance and quality of the content.

The search process

In simple terms: A search query via Google is “sent to the index” and there all documents that serve this search query or contain parts of it are selected and placed in order depending on ranking factors: the Google results page appears.

How does the Mobile First Index work?

The fact that Google has switched to the mobile index means that only the mobile version of a website enters the race for every search query. Information that the “mobile” crawler did not see is not included in the ranking – regardless of whether this information is possibly available in the desktop version.

In practice this means: Anyone who uses different URLs or dynamic serving and slims down the mobile content of a website for reasons of usability runs the risk of not ranking even with desktop search queries, although they have relevant content available for a corresponding search.

Difference between the Mobile First Index and the ranking signal mobile friendliness

An important distinction is made between the two concepts of the Mobile First Index and Mobile Friendliness that Google has recently frequently used.

These are two well-defined Google principles. The Mobile First Index always refers to the content of a website that is used as a possible result in a search and is intended to ensure that the content is actually available for mobile devices.

The ranking factor mobile friendliness ties in at this point. Only after the possible results are sorted according to relevance and quality will it ensure that websites that have mobile-friendly features will rank better.

Why is Google changing its index?

More and more searches are initiated from mobile devices.

For reasons of space and loading time, websites often did not provide the same content on their mobile documents as on the desktop version. Because of this, websites could rank in mobile search queries that did not contain all the desired information in their mobile version.

With the change of the indexed version from desktop to mobile, Google ensures that a website is only displayed to mobile searchers if the information they are looking for is actually available on the mobile site.

How can I build the mobile version of my website?

Responsive design

With responsive web design there is only one version of the page and this is automatically adapted to different screen sizes via CSS. Google currently prefers this approach and has its own page on the basics of responsive web design .

Different URLs for desktop and mobile

The use of different URLs for the content of a desktop and mobile page is no problem for Google, as long as the versions are marked in such a way that Google can recognize which one it is. Google also offers helpful information on the different URLs on its Google Developers platform .

Dynamic serving

The provision of different content on a URL – depending on the querying end device – is another option for delivering your own content. This dynamic provision is technically complex, but can be the right choice for extensive and complex internal systems. Of course, there are also help documents from Google for dynamic provision .

The difference between hiding and omitting

Regardless of the implementation, the main question is which content is presented to the Googlebot in the source code.

With different URLs and Dynamic Serving, it is clear: If content is not delivered on the mobile version, it is invisible to Googlebot and the document cannot rank for this content.

With a responsive design, there are other nuances that need to be considered. Using CSS it is possible to hide content that is in the source text of the document by default. This can be done, for example, by means of an accordion navigation, in which you first have to click on a heading before further text is visible.

For users, this is a helpful design element so that they don’t have to scroll too much on the smartphone. Google explicitly allows this procedure for mobile devices .

However, it is also possible to hide content without giving mobile users the option of showing it with a click. In this case, it can be assumed that Google will ignore this content .

How do I find out whether my website is already using the Mobile First Index ?

If you use the Google Search Console, this is easy: Google will send a message via the Search Console.

The mobile-first email that comes from Google

If the Search Console is not used, the querying Google crawler can be used to conclude that mobile-first indexing has already been activated for your own site. This is the case when the majority of the crawler activity (according to Google about 80%) carries the user agent of the smartphone Googlebot

Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P)
AppleWebKit/537.36 (KHTML, like Gecko) Chrome/W.X.Y.Z‡ Mobile
Safari/537.36 (compatible; Googlebot/2.1;

‡ W.X.Y.Z relates to the current version. See this Google page for more information about Google crawler agent-id.

What if I don’t have a mobile website?

In the event that a domain does not have its own mobile website, Google will continue to crawl the existing desktop page, albeit with the mobile crawler.

What the pros say about mobile SEO

In order to find out which aspects are relevant in practice, we invited 11 of the best SEO experts from Germany, Spain and Great Britain to come to Bonn and asked them central questions about mobile SEO. The English videos are available here.

Conclusion on the Mobile First Index

Depending on your own system and the previous delivery of mobile web content, Google’s switch to the Mobile First Index can mean a lot of work for website operators and SEOs.

In general, Google seems to have learned from the past and has decided against switching all websites to mobile-first indexing on a fixed date. Since only websites for which the desktop and mobile version are compatible will initially be converted, there is still a certain grace period for all webmasters who have not yet dealt with the topic.

The latest information is that all websites will be switched to Mobile First Indexing by Sept 2020.

What google says

Since most users now access Google search via mobile devices, the Googlebot will mainly crawl and index pages with the smartphone agent in the future.