Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare destructiveHint=true, idempotentHint=true and readOnlyHint=false, and the description adds value beyond that: 'Its history stays' clarifies the destruction is scoped, admins-only states the auth requirement, and the quotedMaterial injection warning discloses an unusual prompt-injection attack surface. This is exactly the extra context annotations cannot carry.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.