Launched in March 2018, the Mobile-first index means that Google will now be predominantly using the mobile version of a site’s content for indexing and therefore ranking. Google has been open with information regarding the switch and it seems the aim wasn’t to catch out sites that were desktop only but rather to allow them a chance to advance and make the change to mobile.
After a year and a half of tests and experimentation, the index began to slowly roll out and Google have stated that they are still figuring out some issues surrounding the index.
Previously, Google would index sites based on the experience of desktop users and the content on that version of the site. Separate mobile sites were not contributing to Google’s process of determining your ranking.
The introduction of Mobile-First Index means Google will be able to index and rank your site based on the mobile experience. This move is in response to the increased use of mobile devices and should result in a more accurate reflection of website quality as well as encourage those who hadn’t been considering their sites mobile experience to do so.
Ideally, you should already have a mobile-friendly or preferably responsive site as you risk isolating over 55% of web users if not.
If a site is built in responsive design Google will essentially see the same information from the desktop and mobile versions of the site. If not, there may be a problem when the mobile-first index is applied as Google will now be looking at the mobile version for indexing and ranking purposes. It is important for the mobile site to be optimised to the same standard including content and images.
Having a separate mobile site is still acceptable but is an ageing practice and the best advice to webmasters would be to go. You may be at risk of a negative impact if your mobile website isn’t as strong in terms of quality and content as your desktop version.
It should also be noted that Google will not penalise any sites that have ‘hidden’ content behind accordions or tabs. In the past, they have discredited this website structure and would not give that type of content any real weight when it came to ranking. However, the switch to mobile-first index has caused Google to change their mind due to space issues which is a positive change for web designers organising large amounts of content and trying to maintain a user-friendly experience.