Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden of behavioral disclosure. It explains that the result is a 'dated record of verified past increases' with source and retrieved date, and explicitly denies being a forecast. This provides useful context about the nature and provenance of the data, though it doesn't detail the exact return format.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.