Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already signal read-only, idempotent, and non-destructive behavior. The description adds meaningful behavioral context beyond that: it reports discrepancies, does not smooth over changes, and identifies possible causes (engine version or data restatement). This helps the agent set expectations about the tool's output philosophy.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.