People like things fast. Fast cars, fast food, and fast downloads. Who wouldn't? There's nothing more annoying than sitting on your phone and waiting for something to load. And if something takes too long to load, we move on. That's why performance of a website is so important.
We know from surveys that people expect pages to load in two seconds or less. That's our definition of fast because it's what our users expect. We also know that nearly half of people say they'll abandon a page that takes longer than four seconds to load. In actual testing we know they're a little more patient than that, but if a page takes longer than six seconds, we can expect about half of people to abandon the page.
Websites that load fast aren't just best practice, they're fun. Tweaking a page to reduce its load time is like playing golf. You want get your score as low as possible through careful optimization of techniques.
We curated this checklist to make our own website testing more efficient. We run through it before we launch a client's site. We're sharing it with other designers and developers to make the web as a whole better. You can help by implementing these techniques yourself, sharing them with others, and tipping us off to anything we're missing.