Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds genuinely useful context: the Kyle (1985) regression basis, the direction of interpretation (higher lambda = more illiquid/informed trading), and the output fields including an A-E rating.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.