Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the mutation profile (readOnly=false, idempotent=false, destructive=false, openWorld=true), so the bar is lower. The description still adds real value: the title is escaped and rendered as a heading, the body is optional HTML, and the note 'may sync to iCloud', which contextualizes the openWorld hint. It stops short of stating what happens on duplicate titles or sync failure.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.