Why comments weight heaviest in the ranker
TikTok's FYP ranker uses an engagement-hierarchy: completion > save > share > comment > like > follow. The hierarchy reflects effort — a comment is a higher-friction action than a like, so it carries more weight as a quality signal. Within comments, the ranker further weights comments from accounts the viewer has never previously interacted with — those represent new-connection formation, which the ranker treats as the highest-value engagement outcome. A single high-quality comment from a stranger can move distribution more than 50 likes.
