Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly=true, idempotent=true, and destructive=false. The description adds useful behavioral context: it performs approximate/fuzzy name resolution, returns multiple matches when ambiguous, and is meant as a safeguard before writes. This goes beyond what the annotations alone convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.