Web Performance Metrics Everyone Should Care About
Web Performance metrics can sometimes be a bit arbitrary and diluted by sheer volume. It is important that we call out the ones that we should care the most about. Here is my compilation of metrics to pay the most attention to.
First Contentful Paint (seconds)
First Contentful Paint reflects the time it takes for your application to render it’s first visual elements to the page. By painting early, we give users insight that the page is loading.
First Meaningful Paint (seconds)
First Meaningful Paint is similar to First Contentful Paint except it pertains to the ‘bread and butter’ of your page. Users care about seeing content they were looking for. This metric is the time it takes to see that core content.
Speed Index (seconds)
The Speed Index is calculated by judging completeness of your page render in relevance to time. The goal here is to get low numbers and seek to render your page a soon as possible. Delayed rendering will only hurt your scores. WebPageTest docs do a much better job explaining how this algorithm works for those interested in digging deep.
First CPU Idle (seconds)
Loading web applications tends to take up your CPU during initial load. While the CPU is busy, it becomes difficult for user actions to register and be processed with low latency. This metric aims at finding how long until the CPU is free to process these user actions.
Time to Interactive (seconds)
Time to Interactive measures when the page is ready for user interaction. This typically includes a majority of event listeners are already registered and your application is essentially ‘open for business’ to user interaction. You want to drive this number as low as possible to ensure your users feel that your application is responsive as soon as the content loads.
First Byte (seconds)
This is the time it takes for the browser to receive it’s first bytes from the server. This is important for measuring server latency and it is an easy win to make sure your application is within average thresholds. Some delay is expected so you are really looking for low numbers.
