First Contentful Paint (FCP) is a performance metric that measures the time it takes for the first visible element to be rendered on a web page. It marks the point when the user perceives the web page to be loaded and the primary content becomes visible.
FCP is an important metric because it provides a meaningful user experience indicator. It gives developers and website owners insights into how quickly their web page loads and how quickly users can access the main content. A faster FCP generally leads to better user engagement and satisfaction.
To measure FCP, browsers track the time when the first DOM element is painted on the page, whether it's text, an image, or a background color. It does not have to be the entire page, but just the part that first becomes visible. This is typically represented by a set opacity change, which signals the start of the FCP recording.
Improving FCP involves optimizing various factors, such as reducing server response time, minimizing render-blocking resources, optimizing CSS and JavaScript, and leveraging browser caching. Techniques like lazy loading can also enhance FCP by deferring the loading of non-critical elements until they are needed.
A good FCP goal is under 1 second, as this ensures a smooth and seamless user experience. However, FCP can vary depending on factors such as network speed, device capabilities, and the complexity of the web page. Thus, it is essential to regularly monitor and optimize FCP to provide the best possible user experience.