Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations supply only destructiveHint=false and a title, so the description carries most of the burden. It does add real behavioral value not in the structured data: the case is visible to all active project members, and private sessions must not be copied in. It stops short of stating required permissions or what happens on failure.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.