Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare non-read-only, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds value beyond them by disclosing the append/preserve semantics ('preserving its ID and revision history') and the concurrency-protection requirement of reading the current revision first, though it says nothing about permissions or error behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.