Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses that a key is required, which is useful, but it does not state whether the tool performs a read-only lookup, how it handles missing keys, whether results are cached, or what the response shape is. The definition of the metric is behavioral but does not cover side effects, authentication behavior, or data-source specifics.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.