Google plans to ship omnibox prerendering in Chrome


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Aug 17, 2014
"Google may soon integrate a new feature in its Chrome web browser that it calls omnibox prerendering to speed up the loading of certain websites in the browser."
Current versions of Google Chrome support prefetching as well, but the process is limited as it does not execute JavaScript or renders the page in advance. The main goal of the feature was to use less memory than full prerendering according to Google while still reducing page load times in the process.

Prerendering speeds up the process of loading websites as some content is preloaded. Google changed the prerendering behavior of Chrome in version 63 when it limited the functionality. While prerendering may speed up the loading of sites, it may also waste resources at times; this happens when content is preloaded that is never seen by the user, e.g., when a site with preloaded content is not accessed at all.

Omnibox prerendering adds more elements to the prerendering process. In particular, Chrome will process the DOM tree construction and script executions. The browser limits the new omnibox prerendering feature to "high-confidence suggestions" only according to the intent to ship discussion on Google Groups.

We would like to ship omnibox (i.e., URL bar) prerendering. With this feature, Chrome will start prerendering the high-confidence omnibox autocomplete suggestions. Chrome is currently prefetching resources for high-confidence suggestions using No-state Prefetch, but with this feature we will be further processing the webpage, including the DOM tree construction and script execution.

Websites that are selected by Chrome for the process are "loaded before the navigation is committed", Google notes. Chrome will support a basic API that websites may use to find out if it is prerendered and when it was activated.
The new omnibox prerendering feature will be supported on all platforms that Chrome is available on. Google plans to introduce it on Android first before it becomes available on other platforms. Chrome users may set an experimental flag in the browser to enable the feature right now in Chrome.
  1. Load chrome://flags/#omnibox-trigger-for-prerender2 in the Chrome address bar.
  2. Set the state of the experimental flag to enabled.
  3. Restart the Chrome browser.
A demo page is available at Demo: Omnibox Prerendering to test the functionality.

The feature should be considered experimental at this point. Work on prerendering version 2 continues at Google.

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