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 results can be filtered by a tag value, but it does not say whether this is a read-only lookup, what the default unfiltered output is, or how filtering behaves when both filterKey and filterValue are present or absent.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.