Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial behavioral detail beyond them: the 7-day price-history verification rule, exclusion of prices raised before a sale, ordering by largest drop, a no-commission ordering guarantee, and the seller-diversity behavior of max_per_seller. This is rich methodology disclosure an agent cannot get from structured fields.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.