Google’s mobile-first indexing: coming March 2021

Mobile-first indexing has been an ongoing effort of Google for several years. Google has enabled mobile-first indexing for most currently crawled sites, and enabled it by default for all the new sites. Google’s initial plan was to enable mobile-first indexing for all sites in Search in September 2020. They realize that in these uncertain times, it’s not always easy to focus on work as otherwise, so they’ve decided to extend the timeframe to the end of March 2021. At that time, they’re planning on switching the indexing over to mobile-first indexing.

For the sites that are not yet ready for mobile-first indexing, we’ve already mentioned some issues blocking your sites in previous blog posts. Now that we’ve done more testing and evaluation, we have seen a few more issues that are worth mentioning to better prepare your sites.

Make sure Googlebot can see your content

In mobile-first indexing, Google will only get the information of your site from the mobile version, so make sure Googlebot can see the full content and all resources there. Here are some things to pay attention to:

Robots meta tags on mobile version

You should use the same robots meta tags on the mobile version as those on the desktop version. If you use a different one on the mobile version (such as noindex or nofollow), Google may fail to index or follow links on your page when your site is enabled for mobile-first indexing.

Lazy-loading on mobile version

Lazy-loading is more common on mobile than on desktop, especially for loading images and videos. We recommend following lazy-loading best practices. In particular, avoid lazy-loading your primary content based on user interactions (like swiping, clicking, or typing), because Googlebot won’t trigger these user interactions.

For example, if your page has 10 primary images on the desktop version, and the mobile version only has 2 of them, with the other 8 images loaded from the server only when the user clicks the + button:

In this case, Googlebot won’t click the button to load the 8 images, so Google won’t see those images. The result is that they won’t be indexed or shown in Google Images. Follow Google’s lazy-loading best practices, and lazy load content automatically based on its visibility in the viewport.

Be aware of what you block

Some resources have different URLs on the mobile version from those on the desktop version, sometimes they are served on different hosts. If you want Google to crawl your URLs, make sure you’re not disallowing crawling of them with your robots.txt file.

For example, blocking the URLs of .css files will prevent Googlebot from rendering your pages correctly, which can harm the ranking of your pages in Search. Similarly, blocking the URLs of images will make these images disappear from Google Images.

Make sure primary content is the same on desktop and mobile

If your mobile version has less content than your desktop version, you should consider updating your mobile version so that its primary content (the content you want to rank with, or the reason for users to come to your site) is equivalent. Only the content shown on the mobile version will be used for indexing and ranking in Search. If it’s your intention that the mobile version has less content than the desktop version, your site may lose some traffic when Google enables mobile-first indexing for your site, since Google won’t be able to get the full information anymore.

Use the same clear and meaningful headings on your mobile version as on the desktop version. Missing meaningful headings may negatively affect your page’s visibility in Search, because we might not be able to fully understand the page.

For example, if your desktop version has the following tag for the heading of the page:

Check your images and videos

Make sure the images and videos on your mobile version follow image best practices and video best practices. In particular, we recommend that you perform the following checks:

Image quality

Don’t use images that are too small or have a low resolution on the mobile version. Small or low-quality images might not be selected for inclusion in Google Images, or shown as favorably when indexed.

For example, if your page has 10 primary images on the desktop version, and they are normal, good quality images. On the mobile version, a bad practice is to use very small thumbnails for these images to make them all fit in the smaller screen:

(Caption: desktop version with normal thumbnails / mobile version tiny thumbnails)

In this case, these thumbnails may be considered “low quality” by Google because they are too small and in a low resolution.

Alt attributes for images

Remember that using less-meaningful alt attributes might negatively affect how your images are shown in Google Images.

For example, a good practice is like the following (meaningful alt text):

Different image URLs between desktop and mobile version

If your site uses different image URLs for the desktop and mobile version, you may see a temporary traffic loss from Google Images while your site transitions to mobile-first indexing. This is because the image URLs on the mobile version are new to the Google indexing system, and it takes some time for the new image URLs to be understood appropriately. To minimize a temporary traffic loss from search, review whether you can retain the image URLs used by desktop.

Video markup

If your desktop version uses’s VideoObject structured data to describe videos, make sure the mobile version also includes the VideoObject, with equivalent information provided. Otherwise, our video indexing systems may have trouble getting enough information about your videos, resulting in them not being shown as visibly in Search.

Video and image placement

Make sure to position videos and images in an easy to find location on the mobile version of your pages. Videos or images not placed well could affect user experience on mobile devices, making it possible that Google would not show these as visibly in search.

For example, assume you have a video embedded in your content in an easy to find location on desktop:

On mobile, you place an ad near the top of the page which takes up a large part of the page. This can result your video being moved off the page, requiring users to scroll down a lot to find the video:

In this case, the page might not be deemed a useful video landing page by our algorithms, resulting in the video not being shown in Search.

You can find more information and more best practices in Google’s developer guide for mobile-first indexing.

Mobile-first indexing has come a long way. It’s great to see how the web has evolved from desktop to mobile, and how webmasters have helped to allow crawling and indexing to match how users interact with the web! We appreciate all your work over the years, which has helped to make this transition fairly smooth. 

We are here to help you if you have any questions, or if you need help getting your website ready for Google Mobile Indexing contact us here

Posted by Yingxi Wu, Google Mobile-First Indexing team

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