Speed Index (SI) is an interesting metric when considering page speed. It is absolutely an indication of your page’s performance, but it is completely different from other user-centric metrics such as First Contentful Paint and Largest Contentful Paint. SI indicates how quickly your site loads above the fold. Or to put it another way, when all content within the user’s viewport is completely visible. When looking at your page’s load times, you’re not likely going to be penalized or rewarded for your Speed Index. That is no reason to ignore it. As a single metric, it’s one of the few that encompasses multiple other metrics and can give you a solid idea of your site’s overall speed, efficiency, and performance.
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