Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose meaningful behavioral details: it handles grouping commas and currency, and excludes non-numeric rows while counting them. This goes beyond a generic 'get stats' statement. However, it does not specify the return format, behavior on empty columns, or what happens if the column does not exist.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.