Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, openWorld. The description adds genuinely new operational context — no API key needed and no quota consumption — which is exactly the kind of cost/access detail annotations cannot express. It does not cover rate limits or sample freshness, keeping it below a 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.