Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent, non-destructive behavior. The description adds valuable epistemic guidance: memories are 'user-provided context, not evidence,' and the current request should override conflicting memory. It also notes the 'accessible brand' constraint, which is useful boundary information beyond the schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.