Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare this a safe, idempotent, non-destructive read, so the bar is lower. The description nevertheless adds genuinely useful behavioral context: results are bounded by differing observation times and missing metrics, warning the agent that conclusions are approximate rather than authoritative.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.