Web performance terms explained in plain English
Largest Contentful Paint
Measures how long it takes for the main content of a page to load. Think of it as when the most important thing on the page becomes visible – usually a large image or block of text.
Interaction to Next Paint
Measures how quickly a page responds to user interactions like clicks and taps. A low INP means your site feels responsive and snappy.
Cumulative Layout Shift
Measures how much things move around while the page loads. Have you ever tried to click a button and it suddenly jumped away? That's what CLS catches.
First Contentful Paint (FCP)
Measures when the first piece of content appears on screen. This could be text, an image, or any other visible element.
Total Blocking Time (TBT)
Measures how long the main thread is blocked during page load. High TBT means the page feels frozen and won't respond to clicks.
Speed Index (SI)
Measures how quickly the visible parts of your page load. A lower Speed Index means content appears faster.
Time to First Byte (TTFB)
Measures how long it takes for the first byte of data to arrive from your server. Fast.site can dramatically improve this through edge caching.
Time to Interactive (TTI)
Measures how long until the page is fully interactive. This is when all buttons and links work reliably.
Performance data collected from real users visiting your site through Chrome. This is the most accurate reflection of actual user experience over the past 28 days.
Performance data collected in a controlled test environment. Great for debugging and testing changes, but may not reflect real-world conditions.
Google's automated tool for auditing web page quality. It tests performance, accessibility, SEO, and best practices.
Google's dataset of real user experience metrics. This is where Field Data comes from – actual Chrome users visiting your site.
CSS and JavaScript files that prevent the page from displaying until they're loaded. Minimizing these helps your page appear faster.