Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden, and it does disclose the content returned (source/date/licence/citation). However, it says nothing about whether the metadata is static or cached, when it was last refreshed, or any doubt about the value beyond 'attribute a figure correctly'. For a zero-param metadata read the risk is low, so a middle score is fair.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.