Website Performance

Website performance involves making web pages load quickly, or failing that, making slow processes appear to be fast. This is important because, if your page is slow to load, people will give up waiting for it to load and go somewhere else.

What is performance?

The simplest explanation of performance is how fast your page loads. A slightly more complex explanation is the visitor’s perception of how long it takes to load.

The page needs to load quickly, and enable the user to start interacting with it as soon as possible. If something takes a long time to load, the page needs to indicate that it is loading. Scrolling and animations should be smooth.

Why does performance matter?

If your page is slow to load, visitors will give up and visit a different website instead. The metric associated with this is called bounce rate, which is a measure of how quickly, and how often, users leave your website without visiting a second page.

How is performance measured?

There are several objective measures of performance which get added together to give an overall measure of how well your web page performs:

• First Contentful Paint measures how long it takes the browser to display the first piece of DOM content when someone visits your page. 
• Largest Contentful Paint measures how long it takes until the biggest piece of content is displayed on the screen.
• Speed Index measures how soon content is visually displayed when the page is loading.
• Total Blocking Time measures the amount of time that a page is prevented from responding to user input (e.g. mouse clicks, screen taps, or key presses).
• Cumulative Layout Shift measures unexpected layout changes during the entire lifecycle of a page. For example, if you add an image but don’t specify its width and height, it will cause other elements on the page to move when it has loaded.