Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive and closed-world behavior, so the safety profile is covered. The description still adds genuine value by disclosing that matching is semantic ('search it by meaning') rather than keyword, and that results are ranked best-matching passages rather than whole articles. It stops short of mentioning ranking or threshold behavior, but the gap is modest.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.