Definition
First Input Delay (FID) is a metric that measures the time it takes from when a user first interacts with a web page (such as clicking a link or tapping a button) to the time when the browser begins processing that interaction. It is expressed in milliseconds and focuses on the delay in event processing.
User Cases
FID is used to assess the responsiveness of a website. For instance, when a user clicks a button on a web page, FID measures the delay before the browser starts processing the click event. This metric is particularly relevant for pages with heavy JavaScript execution, where users might experience noticeable delays.
Why It Matters for SEO
Although FID is no longer a Core Web Vital, it was crucial for evaluating user experience by measuring interactivity delays. A low FID score indicated a responsive site, which contributed to better user satisfaction and engagement, indirectly affecting SEO performance. Its successor, Interaction to Next Paint (INP), continues to emphasize the importance of interactivity in SEO.
Related Concepts
Related concepts include Interaction to Next Paint (INP), which has replaced FID as a Core Web Vital, and First Contentful Paint (FCP), which measures how quickly content is visually displayed. Together, these metrics help evaluate a site’s performance and user experience.