The mobile-first indexing is exactly what it looks like. This means that the mobile version of your website is included in Google’s index, and you start the basis of how the ranking determines if you monitor crawlbot traffic on your site. The webmasters can also observe the increase in Googlebot traffic and it will cache the mobile versions of the pages.
This is called “first on mobile device” because it is not just an index for mobile devices: For example, if a site is not a customized version for mobile devices, then the desktop site can still be included in the index. But the lack of optimized experience for mobile devices can have a negative impact on the ranking of that site, and the site with better mobile experience increases ranking can be found, even for those people who are looking at the desktop.
How does it work?
As per the Google press release, it is confirmed that the mobile version will be considered as the main version of your website. If your website is having both the mobile and desktop versions then the mobile version will be optimized for its responsiveness. This latest change applied by Google will have a vast impact on your website in terms of performance. However, it represents a fundamental investment the way Google is thinking about the contents of its website and provides priority for tracking and indexing.
Although you should remember that the website will be considered as the main desktop, the mobile site will be treated as an alternative version for special cases. This is why Google has encouraged webmasters to separate mobile sites by marking the domain with m.domain.com. Google cannot even attempt to crawl and cache mobile versions of all these pages, because they can only search that URL for the mobile device’s search engine.
Mainly this view of the desktop version is often in practice that means desktop site data markup will be done on priority basis by SEO and marketing teams and with the complete content was treated as the complete version of a website, structured, international tag, most backlinks, etc. While the mobile version may contain a lighter material, and/or the same level tagging and structure may not be included, and almost certainly not the most back and outer focus.
With a mobile site, you will need to make sure that your mobile version contains every element that your desktop site does. Although, this could be a lot of work, but will create positive impact on your mobile strategy so far.