Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context: it searches only accessible conversations and does not search message bodies, directing the agent to use returned IDs for message retrieval. It does not add auth/rate-limit details, but those are less critical here.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.