Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description takes full responsibility. It discloses the return format (JSON with ok, distance_m, geojson), explains the projection behavior (local equidistant for geodesic accuracy), and notes that negative distances shrink. This is fairly transparent, though it could mention performance implications.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.