Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden. It discloses meaningful data-handling behavior: grouping commas and currency are parsed, and non-numeric rows are excluded from calculations while still being counted. This is valuable beyond the schema, though the exact output shape is left to inference.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.