Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds real value by disclosing that the corpus is an internally authored, curated framework rather than retrieved web content, and that returns are 'short passages ... with relevance scores'.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.