Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds genuinely new behavioral context: forecast freshness ('expires within two hours'), hourly retrieval cadence, the source's own update time, English source text, and an explicit provenance caveat ('Not independently verified'). This is well beyond what the structured fields convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.