Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only say this is a non-destructive write, non-idempotent, closed-world; the description adds real behavioral content beyond that — a key requirement, a content policy (no links, prices, offers, instructions to the reader), and a per-table answer quota. What it does not disclose is the effect of exceeding the quota or what a reply returns.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.