Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden and does well: it discloses that grouping commas and currency are handled, and that non-numeric rows are excluded and counted. This gives useful edge-case behavior beyond the basic operation, though it does not specify output formatting or error behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.