Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint and closed-world, so the safety profile is covered. The description adds a useful policy fact — that booking is only possible through the official calendar — which is context beyond the annotations, but it does not describe the shape or scope of what is returned.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.