Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish read-only, idempotent, non-destructive behavior. The description adds one useful behavioral trait beyond those: pinned dashboards are filtered by the calling identity's visibility, which is important context an agent could not infer from the schema or annotations. It does not detail return-value shape, but the most safety-relevant behavior is covered.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.