Key performance indicators

The first step to creating a fast site or improving an existing site is to use tools to measure your performance and knowing what to measure. You should create a performance baseline and make iterative changes to improve your performance profile.

In this section, I will review different metrics you should measure, why you need to track them, and how to improve them.

Time to first byte

The time it takes to retrieve the first response byte is the time to first byte. This moment starts the response download. The most important network request is for the document. Once downloaded, the rest of the network resources (images, scripts, style sheets, and so on) can be downloaded.

You can break down the time...