Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover safety (readOnlyHint=true, destructiveHint=false) but say nothing about throttling; the description adds a free-answer-per-day quota and a specific error-handling protocol (relay limit_reached, do not retry). That is real behavioral context the structured fields do not carry.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.