Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond annotations (readOnly, idempotent, non-destructive), the description adds meaningful behavioral context: notes are sorted newest-first, they survive member removal, and they require mod authority with complete privacy from the member. This directly helps the agent anticipate impact and permissions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.