Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden and does well: it discloses defaults (level='county', country='ireland'), the slim-by-default return shape, and exactly what `include_parents=True` adds. It doesn't cover error behavior or whether unknown levels raise or return empty, which is the remaining gap.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.