Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds useful behavioral context beyond that: hard limits of 'up to 20 websites' and '20 most recently active conversations', plus the optional single-website scoping.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.