The mobile-first index is without doubt one of the greatest shifts in Google in recent history, and probably one of the largest we’re likely to see for some time. Technically this isn’t a separate to the incumbent index, but is a fundamental shift in how content and URLs are crawled, weighted, and ranked.

Today we’re announcing that after a year and a half of careful experimentation and testing, we’ve started migrating sites that follow the best practices for mobile-first indexing.

Mobile usage surpassed desktop in 2015, and this response from Google comes as really the end point of a journey that started with the April 2015 Google update, dubbed Mobilegeddon.

Google has been talking about the mobile-first index since late 2016, both via their Webmaster Blog, and publicly at conferences like PubCon and SMX, so it’s not something that’s new and shouldn’t be taking SEOs by surprise.

One thing that might be taking some people by surprise however, is the timing.

We know that Google has been testing for some time and have made announcements that certain ranking factors, such as site speed, will be weighted differently in the coming months, and for many it was expected that the mobile-first roll-out would happen closer to then.

This is why a prominent mobile SEO strategy has been important since 2015, so a lot of websites should already be prepared.

Separate desktop and mobile websites

Google’s John Mueller publicly told us during a Google Webmaster Hangout in June 2017, that if you’re operating separate m-dot and desktop URLs, it’s probably best to perform the migration before the mobile index is rolled out at.

Having separate mobile and desktop URLs will cause issues as Google is more likely to include the m-dot version.

Dynamic versus responsive websites

Google has been advocating the responsive approach in its literature and messaging, but a lot of websites out there have gone with the dynamic approach.

On a responsive site Google crawls the website with both desktop and mobile user agents (it’s important to remember the desktop agent still exists), and both will crawl the same URL and determine which version to return content based on the user.

With dynamic sites Google must crawl with both user agents to determine which version is the mobile version.

This is where a variable HTTP header comes into play, and there are a large amount of dynamic websites not utilising a variable HTTP header.

This isn’t an exhaustive item to implement and can save a lot of time in making things easier for Google and other search engines to establish which version of the URL is the mobile version.

How do I know if I’ve already been included in the index?

In Google’s blog post announcing that tit is rolling out the index, it has confirmed a number of things that employees have been saying through Twitter and other channels:

We are notifying sites that are migrating to mobile-first indexing via Search Console. Site owners will see significantly increased crawl rate from the Smartphone Googlebot. Additionally, Google will show the mobile version of pages in Search results and Google cached pages.

And for reference, this is the Smartphone Google bot full user agent string for log file analysis:

What do I do if I’m not prepared?

If you’re running separate m-dot and desktop websites, or a dynamic website that hasn’t been configured to technical best practice, you’re now in a race against the clock, even more so if your competitors are fully mobile ready.

Being responsive isn’t the only thing you need to consider, you need make sure that your other directives and signals matchup to your new structure.

Things like version local HREFLANG, correct canonical tags, and fast page load speeds and rendering are important. offers a range of mobile services, including numerous mobile site audits. If you want to know more about how we can help your site for mobile-first, check out our contact page.