Google’s Mobile First Index is Google’s pivot to using mobile versions of websites when it comes to indexing and ranking sites in the search results pages (SERPs). This has been a reflection of the increasing use of mobile phones to browse the web, access websites and, most importantly, search for sites and businesses using Google’s search engine.

Whilst it is not recommended to have separate mobile and desktop versions of the same site (as content can easily differ and this can be an issue) most modern CMS’s can generate a mobile ‘version’ of the original site using CSS which will adjust elements of the website’s design based on screen width. These are then placed for optimal display on a mobile or tablet (ie a narrower portrait view for mobile devices). 

Whilst the mobile version will be displayed to mobile users and desktop version displayed for desktop users, Google will only use the mobile version of the site when indexing. This has meant that websites that aren’t optimised for mobile, or don’t have mobile versions, are at a disadvantage in the SERPs compared to their mobile optimised peers.


Google’s Mobile First Index as a concept has been around since the end of 2017, when it was announced to be rolled out. In March 2018 Google announced that websites would need to prepare for a full rollout, but it has been since July 2019 that all new, or previously unindexed websites, have been subjected to Google’s Mobile First index methods. 

Google initially planned to launch a full rollout to all websites in March 2020 but pushed this back to 2021, citing uncertain times’ in a blog post.

Why Google Switched To Mobile First Index

The move by Google to mobile first indexing is a reflection of the changing way in which people are using the internet, with the growth in the popularity of mobile devices such as smartphones and tablets now performing the majority of search queries conducted on its search engine. 

Google recognised this back as early as 2016. At this time, rankings and indexing were based entirely upon the desktop version of websites, which was frequently superior to the mobile version that was more commonly visited by internet users clicking through from their Google search. As a result, the rankings and indexing did not accurately reflect the experience of the majority of Google’s users.

There is no facility to opt in or out of mobile first indexing, which means that all websites must now be developed with a focus on the mobile experience equalling that of desktop users if they hope to be fully optimised for search.