Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish this is a non-destructive, non-open-world write (readOnlyHint=false, destructiveHint=false). The description adds genuinely new behavioral context the annotations do not carry: who can see the note ('the owner sees the note in the viewer') and the thread audience ('the owner and whoever started it'), plus the visibility gate implied by 'any presentation you can see'.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.