I have many tools in my web performance toolkit. Chrome DevTools is my goto for inbrowser performance analysis. I use the PageSpeed Insights and YSlow extensions for converting performance observations into actions. I love bookmarklets, especially for doing performance analysis in mobile browsers. The websites I run are monitored using several RUM and synthetic performance measurement services.
But I rely on WebPageTest more than all of these other tools combined. Why?
You can run WebPageTest from anywhere. It doesn’t require installing anything, all you need is a browser. I’ve frequently run an analysis of someone’s website in IE from China on my iPhone and shown them the results midconversation. They’re amazed, and I have to swing the conversation from explaining how such a powerful analysis can be done so quickly on my phone to what they need to do to make their website faster.
WebPageTest makes it easy to save and share results. When analyzing performance, it’s often hard for one person to convey their experience to other team members. Sharing a WebPageTest URL ensures that everyone is looking at the same experience. This is especially helpful in bug reports. Since results are never deleted, it’s possible to go back to review performance problems in older browsers and previous versions of the website.
WebPageTest covers a wide range of performance metrics. It has waterfall charts with the associated request and response headers. It has timing metrics including time to first byte, document complete, and fully loaded. WebPageTest breaks down the number of requests and bytes by content type. Users who look deeper find the CPU utilization, bandwidth, and main thread timelines, which are often the key for uncovering the most critical performance fixes.
More than anything else, WebPageTest is constantly innovating in the space of web performance. Ten years ago everyone tracked window.onload as a reflection of how long it took for a user to start experiencing a website. And ten years ago that was a satisfactory approximation. But today’s websites use AJAX, preloading, async loading, lazyloading, and other advanced techniques, which means we can no longer rely on window.onload to be an accurate reflection of what the user sees.
WebPageTest leads the way in finding new ways to measure and convey the user experience. This started with its focus on filmstrip views and side-by-side videos. Highlighting start render time lets website owners know how long users are waiting to get an indication that the website is even alive and able to respond to their requests. The most important innovation is the development of the Speed Index metric: one number that summarizes the overall rendering experience.
WebPageTest is the leading web performance tool in the world today. It is easy to use, provides the performance metrics that matter, and is pioneering new ways to measure the actual user experience that websites deliver. In 2009’s Even Faster Web Sites, I wrote that WebPageTest “hasn’t gotten the wide adoption it deserves.” Fortunately, that’s no longer true. In fact, now there’s even a book about it! Read on and find out how to get the most out of WebPageTest to help you deliver a web experience that is fast and enjoyable.
—Steve Souders, Chief SpeedCurver at SpeedCurve, “working on the interplay between performance and design” - http://stevesouders.com