Google has released version 2 of the PageSpeed Insights API which includes support for rule groups such as speed or usability, more information about speed and score, and a clearer format for text-responses. Google PageSpeed Insights is a tool that analyzes the performance of a web page and returns PageSpeed scores and information on how to improve the load time. PageSpeed Insights can analyze the performance of a web page for both mobile devices and desktop. The PageSpeed Insights API returns various statistics for a specified web page including the response bytes for the main HTML document, CSS resources, JS resources, image resources, and more.
This latest release of the PageSpeed Insights API focuses on improving mobile performance which according to Google, web pages should render "in under a second on a mobile network." Google also states in the PageSpeed Insights mobile analysis documentation that:
"The whole page doesn’t have to render within this budget [render in under a second], instead, we must deliver and render the above the fold (ATF) content in under one second, which allows the user to begin interacting with the page as soon as possible. Then, while the user is interpreting the first page of content, the rest of the page can be delivered progressively in the background."
There is an API explorer that can be used to play around with the PageSpeed Insights API. If you want to find out the overall performance of a web page, check out the online version of PageSpeed Insights. John Mueller, webmaster trends analyst at Google Zurich, suggests in his Google+ announcement post that developers could use the PageSpeed Insights API to create a physical speed meter for their website homepage. Developers could also use the PageSpeed Insights API along with Google Gauge Charts (Part of the Google Visualization API) to create a web-based dashboard that visualizes the performance metrics of specific web pages.
Developers interested in using the PageSpeed Insights API can find more information on the Google Developers website.