Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnlyHint=true), yet the description adds material context: pricing at 50 cents per call, the fact that an API key does not cover it, and what each result contains (entry fields or candidate lists). That is genuine behavioral value beyond the structured fields.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.