GTmetrix: Speed That Pays Off – Run a speed test—PageSpeed and YSlow scores drop from 4s to 1.5s after zapping JS and 20+ hefty images—while Waterfall charts unpack 50+ resources with load times and sizes. Core Web Vitals (LCP,CLS) call out user experience gripes,tossing fixes like caching or CDN boosts. Free tests pick spots like Vancouver; $10/month Pro tracks 20 URLs with history and API perks. A pet store owner I know flipped its tips into a traffic surge—3K to 6K visits in a month after a mobile slump,climbing ranks 20%—site owners and devs lean on it for technical SEO and keeping users clicking happily.