Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations present, the description fully carries the burden and is unusually thorough: it discloses read-only status, no side effects, no storage, no API key, decaying confidence, and that output is a typical-day shape rather than per-day certainty. It also states the returned artifacts (curve, peak, dip, score, best/worst days).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.