Kishore
Rahul
By Rahul Bansal and Kishore Simbili, PageSpeed Team

We spend a lot of time working to make the web faster. Last year, we introduced PageSpeed Service, an online service that automatically speeds up loading of web pages.

We are constantly working on new optimizations (rewriters) that can make pages load even faster. Along these lines, we are introducing a new rewriter called "Cache and Prioritize Visible Content". This rewriter enables users to start interacting with the web page and consuming the content much sooner. It accomplishes this by optimizing the page as a whole using the following web page-aware techniques and with minimal configuration needed:
  • Make HTML cacheable. Typically, most web pages are not cached because they contain small amounts of personalized information or other non-cacheable data. This rewriter separates the non-cacheable portions from the HTML and enables caching for the rest of the content on PageSpeed servers. When the page is loaded, PageSpeed servers send the cacheable parts immediately while non-cacheable parts are fetched from the origin server & patched into the browser later.
  • Prioritize visible content rendering. Rendering of a modern web page requires several network resources, but not all of them are needed right away. This rewriter automatically determines and prioritizes the content that is above the fold of the browser, so that it doesn’t have to compete with the rest of the page.
  • Defer Javascript. JavaScript execution is deferred until page load so that it doesn’t block rendering of visible content.

Early deployment of these techniques has shown significant improvements in user-perceived page load times. Below is a filmstrip view that compares the loading of pages on Power Line, a US-based political commentary website.


Joe Malchow, Publisher of Power Line says "With this rewriter the most important bytes, our content, load first and fast. To our readers, Power Line appears to be completely instantaneous, prompting deeper and lengthier reading sessions and more profound engagement with the site."

This rewriter works best when the page content is mostly generated on the server rather than via Javascript and only small portions of it are personalized. To see how this rewriter would benefit your site, you can check it out here. If you are satisfied with the results, you can sign up for PageSpeed Service here. If you already use PageSpeed Service, you can find more details about enabling this rewriter here. This rewriter will also be available to App Engine users of PageSpeed Service in the near future.


Rahul Bansal and Kishore Simbili are Software Engineers on Google’s PageSpeed Team in Bangalore, India, which is dedicated to making the web faster.

Posted by Scott Knaster, Editor