Using WebPageTest

Chapter 1. How Fast Is My Page?

The first question to pop into the minds of most people tasked with optimizing the performance of a web page is probably “How fast is it?” As in the story about the factory, understanding the current state of a system is an important first step on the road to optimization. Determining the current speed of a page helps to dictate the severity of the performance problem and sets a baseline from which to improve.

Before diving into WebPageTest for the purpose of getting the one golden number that represents the true speed of your page, take a step back and consider two cautionary points. First, the golden number you seek may not be the metric provided by the tool. If you want to know the speed of a page, you should define exactly what you’re trying to measure. Second, even if the tool did report on the metric you care about, it is not necessarily representative of the page’s true speed. The true speed is that which the real users of the page experience. Real users live all over the world, use different technologies like device type or browser, and connect to the Internet differently. The true speed of this amalgamation is extremely hard to reflect in a single test.

Measure What Matters

WebPageTest measures the speed of a web page based on the amount of time that has elapsed from the initial page request until the browser fires the load event, sometimes referred to as the document complete time. This is the time at which the Document Object Model (DOM) ...