Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations, so the description carries the burden. It adds genuinely useful behavioral context: the response includes a provenance block with sample counts, and warns that sparse vs. dense curves look identical without the count. That is real operational guidance an agent wouldn't infer from the schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.