Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations supplied, the description carries the full behavioral burden, and it does disclose the four content categories returned (source, date, licence, citation). The read-only nature is implicit in a zero-parameter metadata lookup, but the description says nothing about return format or whether the dataset identifier is fixed.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.