Type an address, press Enter, and within a second your browser has looked up a name, opened an encrypted connection to a machine that may be on another continent, requested a document, and parsed, styled, laid out and painted it while fetching dozens more files. Every tool and optimization in this book plugs into some step of that journey.
Knowing the steps pays off quickly. A slow page is slow at a specific stage: DNS, the handshake, the server's think time, a render-blocking stylesheet or a long JavaScript task. A feature that "doesn't work in Safari 10 " is usually a question of which engine implements which standard, and when. The subsections below follow a request from the network to the pixels, meet the organizations that write the rules, and map the tools you will install later in this chapter.