Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered without the description. The description adds that rates come either live from the Grand Bazaar or from a reference source, which is genuine behavioral context about data provenance, but it says nothing about rate freshness, rounding, or failure modes for unsupported currency codes.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.