WebBuilding

Events and eras

Mobile-first indexing

Summary

Mobile-first indexing is Google Search's practice of crawling websites with a smartphone crawler and using the mobile version of each page for indexing and ranking. Google announced the first experiments on November 4, 2016, began moving sites in larger numbers on March 26, 2018, and declared the move complete on October 31, 2023. After July 5, 2024, it crawled the last remaining sites with its smartphone crawler only.

Web Building Encyclopedia · Events and eras · Last reviewed October 22, 2026 · 9 min read

What mobile-first indexing is

Mobile-first indexing is the way Google Search builds its index. Google visits a site with a crawler that behaves like a smartphone and uses the mobile version of each page’s content for indexing and ranking.1 The index is the database of pages a search engine looks through when someone searches, and a crawler is the program that fetches those pages.

Google runs two main crawlers. Googlebot Smartphone simulates a visitor on a mobile device, and Googlebot Desktop simulates a visitor on a desktop computer. Because Google indexes mobile content first, most of its crawl requests for most sites come from the smartphone crawler.2 Both crawlers obey the same product token in robots.txt, the file that tells crawlers what they may fetch, so a site cannot allow one there and block the other.2

Three points are often confused:

  • There is one index. When the large-scale rollout began in March 2018, Google wrote that it did not keep a “mobile-first index” separate from its main index.3
  • It changes how content is gathered, not how it is ranked. The same post said that content collected this way has no ranking advantage over content that is not, and that sites with only a desktop version stay in the index.3
  • It is separate from mobile-friendliness. Mobile-friendliness, meaning a page that is easy to use on a phone, became a larger ranking signal for mobile searches in April 2015.4 Mobile-first indexing, announced in November 2016, decides which version of a page Google reads.5

The change followed where people browse. StatCounter, a web analytics company, reported that phones and tablets made up 51.3% of worldwide internet use in October 2016, against 48.7% for desktop computers, the first time mobile had come out ahead.6 As of September 2026, StatCounter puts mobile at 58.99% of worldwide page views, desktop at 39.26% and tablet at 1.76%.7

The mobile-friendly years (2014 to 2016)

Responsive design, the setup Google now recommends, came before any of these changes. On May 25, 2010, Ethan Marcotte published “Responsive Web Design” in A List Apart, describing one layout that adapts to any screen. He named fluid grids, flexible images and CSS media queries as its three technical ingredients.8

On November 18, 2014, Google began adding a “mobile-friendly” label to its mobile search results, rolling out worldwide over several weeks.9 Googlebot gave the label to pages that:

  • avoided software that is uncommon on mobile devices, such as Flash;
  • used text that could be read without zooming;
  • sized content to the screen, so visitors did not have to scroll sideways or zoom;
  • placed links far enough apart that the right one was easy to tap.9

The same post said Google was experimenting with these criteria as a ranking signal.9 The plugin’s later decline is covered in the end of Adobe Flash.

On February 26, 2015, Google announced that from April 21 it would expand its use of mobile-friendliness as a ranking signal, for mobile searches in all languages worldwide.10 The update began rolling out on April 21, 2015. It changed only mobile rankings and judged each page on its own, not whole websites.4 Google added that the intent of the search was still a strong signal, so a page that was not mobile-friendly could still rank well if its content matched the query.4

On March 16, 2016, Google said an update starting in May 2016 would increase the effect of the mobile-friendly signal, and that sites that were already mobile-friendly would not be affected.11

On August 23, 2016, Google reported that 85% of the pages in its mobile results met the mobile-friendly criteria, and it removed the label to reduce clutter. Mobile-friendliness stayed a ranking signal.12 The same post announced a new signal against intrusive interstitials, pop-ups that cover a page’s content. After January 10, 2017, pages whose content was hard to reach because of them could rank lower. Interstitials required by law, such as cookie notices and age checks, and banners that use a reasonable amount of screen and are easy to dismiss were not affected.12

The announcement and the slow rollout (2016 to 2020)

On November 4, 2016, Doantam Phan, a Google product manager, announced the first experiments with mobile-first indexing. He wrote that most people now searched Google on a mobile device, but that Google’s ranking systems still usually looked at the desktop version of a page. That caused problems when the mobile page held less content than the desktop page.5

The plan was for Google’s algorithms to rely mainly on the mobile version of a site to rank its pages, read its structured data and write the snippets shown in results.5 Structured data is extra code that labels a page’s content, such as a product’s price or an event’s date, for search engines. Google promised small experiments over the following months. Sites whose content and markup were the same on mobile and desktop, as on a responsive site, should not have to change anything, and sites with only a desktop version would still be indexed.5

On December 18, 2017, Gary Illyes of Google wrote that the switch had already started for a small number of sites and that Google had no timeline for finishing it. Each site would be judged on its own and moved when it was ready.13

Google began moving sites in larger numbers on March 26, 2018. Fan Zhang, a Google software engineer, wrote that owners would be told in Search Console, Google’s free tool for site owners, and should expect a large rise in crawling by the smartphone Googlebot.3 The rollout then moved in steps:

  • December 19, 2018. Google said it used mobile-first indexing for more than half of the pages shown in its results worldwide. John Mueller of Google said that, for sites not using responsive design, two problems came up more often in Google’s checks: structured data and image alt text missing from the mobile pages.14
  • July 1, 2019. Mobile-first indexing became the default for new websites that Google Search had not seen before, as announced on May 28, 2019. Existing sites were still checked one by one.15
  • March 5, 2020. Google said about 70% of the sites shown in its results had already switched and that it would move all remaining sites starting in September 2020. The post recommended responsive design for new sites and suggested not using separate mobile URLs.16
  • July 22, 2020. Google moved the deadline to the end of March 2021, noting that “in these uncertain times, it’s not always easy to focus on work.”17

Delays and completion (2021 to 2024)

The March 2021 date passed without the move finishing. On November 26, 2021, Mueller wrote that Google had switched the majority of web pages to indexing with Googlebot Smartphone, but that some sites were still not ready because of unexpected challenges. Google set no new final date.18

On October 31, 2023, Mueller and Nir Kalush of Google announced that the move to mobile-first indexing was complete. They traced the effort back to the mobile-friendly update of 2015 and the start of mobile-first crawling in 2016.19 Google said it knew of only a very small set of sites that did not work on mobile at all. Typical faults were errors shown to every mobile visitor, mobile pages blocked by robots.txt while desktop pages were allowed, and every mobile page redirecting to the home page.19 Google would keep crawling those sites with its older desktop Googlebot for the time being, and it turned off the indexing crawler information on the Search Console settings page.19

Google’s mobile testing tools went soon after. As announced on April 19, 2023, Google began retiring Search Console’s Mobile Usability report, the Mobile-Friendly Test tool and its API on December 1, 2023.20 An update note on the 2016 post that introduced the test says the test and the report were retired on December 1, 2023.21 Google stressed that this did not mean mobile usability had stopped mattering in Search.20

The last step came in 2024. On June 3, 2024, Mueller wrote that after July 5, 2024 Google would crawl and index the remaining sites with only Googlebot Smartphone, and that sites whose content could not be reached on a mobile device at all would no longer be indexable.22 Googlebot Desktop can still appear in server logs, he added, because some features, such as product listings and Google for Jobs, still use it in certain cases.22

What Google reads on the mobile version

Google’s current guidance, last updated on December 10, 2025, says a mobile version is not required for a page to appear in results but is very strongly recommended. It describes three ways to build a mobile site:1

SetupHow it worksGoogle’s view
Responsive designThe same HTML at the same URL, laid out differently for each screen sizeRecommended as the easiest to implement and maintain1
Dynamic servingThe same URL, but the server sends different HTML to each kind of device, signaled with the Vary HTTP headerSupported1
Separate URLsA different address for mobile, often called an m-dot site, with redirects based on the deviceSupported, but Google suggested not using it in 202016

With responsive design the content and metadata are already the same on every device. For the other two setups, the guidance lists what has to match:1

  • Content. The mobile page should carry the same primary content and the same headings as the desktop page. Tabs and accordions are acceptable.1 Google’s 2020 post said only the content shown on the mobile version is used for indexing and ranking.17
  • Loading. Primary content should not wait for a tap, swipe or typing before it loads, because Googlebot does not do those things.1 Content that loads as it comes into view is fine.17
  • Robots meta tags. Use the same tags on both versions. A noindex or nofollow tag on the mobile page alone can stop it being crawled or indexed.1
  • Structured data and metadata. Use the same structured data, with links pointing at the mobile addresses, and equivalent titles and meta descriptions.1
  • Images and video. Use good-quality images, stable image addresses and the same alt text, and place videos where they are easy to find on a phone.1 Blocking image or CSS files in robots.txt can drop images from Google Images or stop pages from rendering properly.17
  • Separate mobile sites. Return the same error status on both versions, do not send every desktop page to the mobile home page, and make sure the server can handle more crawling.1

Responsive pages also rely on a viewport meta tag. Some mobile browsers lay a page out in a virtual window wider than the screen (980 pixels in MDN’s example) and shrink it to fit, so media queries written for narrow screens may never apply; the viewport meta tag addresses this.23

Speed and page experience

Google also added other signals aimed at phones. On January 17, 2018, it announced the Speed Update: from July 2018, page speed would count in mobile search ranking, having been used before only for desktop searches. Google said it would affect only the pages with the slowest experience and a small share of queries, and a later note says it rolled out to all users on July 9, 2018.24 To measure speed, Google pointed to the Chrome User Experience Report, a public set of measurements from real Chrome users, along with its Lighthouse and PageSpeed Insights tools.24

Page experience came next. Google said it would start using page experience in ranking in mid-June 2021 and that it would reach its full role by the end of August 2021. The set included three Core Web Vitals (Largest Contentful Paint, First Input Delay and Cumulative Layout Shift), plus mobile-friendliness, HTTPS and the absence of intrusive interstitials.25 A later note on that post says Interaction to Next Paint replaced First Input Delay as a Core Web Vital on March 12, 2024.25

In April 2023 Google said page experience is not a single ranking signal. It still recommends that site owners reach good Core Web Vitals for success in Search.20

Timeline

  1. After this date Google crawls and indexes the last desktop-crawled sites with Googlebot Smartphone only22
  2. Google retires the Mobile-Friendly Test and the Mobile Usability report21
  3. Google announces that the move to mobile-first indexing is complete19
  4. Google says most pages have moved but sets no final date18
  5. Google extends the deadline for all sites to the end of March 202117
  6. About 70% of sites in results have switched; all sites planned from September 202016
  7. Mobile-first indexing becomes the default for new websites15
  8. Mobile-first indexing covers more than half of pages shown in results14
  9. The Speed Update brings page speed into mobile ranking for all users24
  10. Google begins moving sites to mobile-first indexing in larger numbers3
  11. Signal against intrusive interstitials on mobile takes effect12
  12. Google announces its first mobile-first indexing experiments5
  13. Google drops the mobile-friendly label as 85% of mobile results qualify12
  14. The mobile-friendly ranking update begins rolling out worldwide4
  15. Google starts labeling mobile-friendly pages in mobile results9

What it means for your website

Since July 2024 Google crawls and indexes sites with its smartphone crawler only, apart from a few features.22 Whatever is missing from your mobile pages is missing for Google too.17

  • Use one responsive site. Google recommends responsive design as the easiest pattern to maintain.1 On WordPress or a hosted website builder, choose a theme or template built for responsive design.
  • Do not hide content on phones. Text, photos, reviews or service areas cut from the mobile layout to save space are not indexed. Tabs and accordions are fine.117
  • Check what Googlebot sees. The URL Inspection tool in Search Console shows how Google crawled a page, and the crawl stats report shows which Googlebot visits your site.1619 Also open your key pages on an iPhone and an Android phone.
  • Retiring an m-dot site. Google’s advice is to redirect each mobile URL to its matching responsive URL with a 301 redirect, one URL at a time, and to give each page a canonical tag that points to itself.26 Plan it like any website migration.
  • Keep pop-ups small and pages fast. Pop-ups that cover the content on phones can count against a page,12 and Google recommends good Core Web Vitals.20
  • Ignore advice to use the old tests. The Mobile-Friendly Test and the Mobile Usability report were retired on December 1, 2023.21

For what each builder lets you change for search engines, see our guide to websites and SEO.

See also

References

  1. Mobile site and mobile-first indexing best practices. Google Search Central documentation. 2025-12-10. accessed October 22, 2026.
  2. Googlebot. Google Search Central documentation. accessed October 22, 2026.
  3. Rolling out mobile-first indexing. Fan Zhang, Google Search Central Blog. 2018-03-26. accessed October 22, 2026.
  4. Rolling out the mobile-friendly update. Takaki Makino and Doantam Phan, Google Search Central Blog. 2015-04-21. accessed October 22, 2026.
  5. Mobile-first indexing. Doantam Phan, Google Search Central Blog. 2016-11-04. accessed October 22, 2026.
  6. Mobile and tablet internet usage exceeds desktop for first time worldwide. StatCounter. 2016-11-01. accessed October 22, 2026.
  7. Desktop vs Mobile vs Tablet Market Share Worldwide (September 2026). StatCounter Global Stats. 2026-09. accessed October 22, 2026.
  8. Responsive Web Design. Ethan Marcotte, A List Apart. 2010-05-25. accessed October 22, 2026.
  9. Helping users find mobile-friendly pages. Ryoichi Imaizumi and Doantam Phan, Google Search Central Blog. 2014-11-18. accessed October 22, 2026.
  10. Finding more mobile-friendly search results. Takaki Makino, Chaesang Jung and Doantam Phan, Google Search Central Blog. 2015-02-26. accessed October 22, 2026.
  11. Continuing to make the web more mobile friendly. Klemen Kloboves, Google Search Central Blog. 2016-03-16. accessed October 22, 2026.
  12. Helping users easily access content on mobile. Doantam Phan, Google Search Central Blog. 2016-08-23. accessed October 22, 2026.
  13. Getting your site ready for mobile-first indexing. Gary Illyes, Google Search Central Blog. 2017-12-18. accessed October 22, 2026.
  14. Mobile-First indexing, structured data, images, and your site. John Mueller, Google Search Central Blog. 2018-12-19. accessed October 22, 2026.
  15. Mobile-First Indexing by default for new domains. John Mueller, Google Search Central Blog. 2019-05-28. accessed October 22, 2026.
  16. Announcing mobile first indexing for the whole web. John Mueller, Google Search Central Blog. 2020-03-05. accessed October 22, 2026.
  17. Prepare for mobile-first indexing (with a little extra time). Yingxi Wu, Google Mobile-First Indexing team, Google Search Central Blog. 2020-07-22. accessed October 22, 2026.
  18. A 2021 update on mobile indexing. John Mueller, Google Search Central Blog. 2021-11-26. accessed October 22, 2026.
  19. Mobile-first indexing has landed: thanks for all your support. John Mueller and Nir Kalush, Google Search Central Blog. 2023-10-31. accessed October 22, 2026.
  20. The role of page experience in creating helpful content. Danny Sullivan, Google Search Central Blog. 2023-04-19. accessed October 22, 2026.
  21. The Search Console mobile friendly testing tool (retired). Yaniv Loewenstein, Google Search Central Blog (update note of December 1, 2023). 2016-05-17. accessed October 22, 2026.
  22. Mobile-indexing-vLast-final-final.doc. John Mueller, Google Search Central Blog. 2024-06-03. accessed October 22, 2026.
  23. meta name="viewport". MDN Web Docs, Mozilla. accessed October 22, 2026.
  24. Using page speed in mobile search ranking. Zhiheng Wang and Doantam Phan, Google Search Central Blog. 2018-01-17. accessed October 22, 2026.
  25. More time, tools, and details on the page experience update. Jeffrey Jose, Google Search Central Blog. 2021-04-19. accessed October 22, 2026.
  26. How to move from m-dot URLs to responsive site. Cherry Prommawin, Google Search Central Blog. 2017-09-14. accessed October 22, 2026.

Web Building Encyclopedia. First published October 22, 2026. Last reviewed October 22, 2026. Every fact on this page is linked to a source we opened. Spotted an error? Write to [email protected].