Performance
What the findings of the performance check mean and how to fix them. The topics follow the categories of the report.
Server and network
What server response time measures
Server response time, or TTFB, measures how long the browser waits for the first byte of a page. Until something arrives, it can neither show anything nor load anything else.
What HTTP/2 and HTTP/3 bring
HTTP/2 and HTTP/3 transfer many files at once over a single connection. With the older HTTP/1.1, files wait for each other and the page loads more slowly.
What compression does
Compression shrinks HTML, CSS and JavaScript before the server sends them, and the browser unpacks them again. It saves a large part of the transferred data and costs hardly any computing time.
Page weight
What makes up page weight
Page weight is the amount of data a browser transfers for a page: HTML, CSS, JavaScript, images and fonts. The less it is, the sooner the page is ready, above all on mobile networks.
What JavaScript costs in load time
JavaScript has to be loaded, parsed and run before it does anything. On weaker phones this often blocks the page for longer than the loading itself.
How images load fast
Images are usually the biggest part of a page. They load fast when they come in the size they are shown at, in a modern format, and only once they come into view.
Rendering
What render-blocking resources are
Render-blocking resources are scripts and stylesheets the browser has to wait for before it shows anything. The fewer there are, the sooner your visitors see content.
How web fonts load fast
Web fonts are font files a page loads on top. They are fast when the text appears at once in a fallback font and only the weights the page really uses are loaded.
What third parties cost in load time
Third parties are foreign domains from which a page loads scripts, fonts, images or embeds. Each one costs a connection of its own, and its speed is out of your hands.
Caching
Core Web Vitals
What the Core Web Vitals are
The Core Web Vitals are three measurements from Google for the experience on a page: how fast the main content appears, how quickly the page responds and how steady it stays while loading. Google takes them into account when ranking pages in search.
What Largest Contentful Paint measures
Largest Contentful Paint, or LCP, measures when the largest visible element of a page appears, usually an image or a heading. Up to 2.5 seconds is good.
What Interaction to Next Paint measures
Interaction to Next Paint, or INP, measures how quickly a page visibly responds to clicks, taps and key presses. Up to 200 milliseconds is good.
What Cumulative Layout Shift measures
Cumulative Layout Shift, or CLS, measures how much content unexpectedly shifts around while a page loads and is used. Values up to 0.1 are good.