The Search Index (SI) metric evaluates how well a web page is prepared for indexing and visibility in search engines. Unlike visual performance metrics, SI focuses on SEO-readiness — including metadata presence, crawlability, structured data, and canonical tags. A high SI score means your page is discoverable, indexable, and optimized for search ranking. Pages with low SI often lack critical elements like titles, descriptions, or proper robots directives. Improving SI involves adding structured data, internal links, meta tags, and fixing noindex issues. Regularly monitoring SI helps ensure your content is not just fast, but also findable and SEO-compliant.