Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds significant behavioral context beyond annotations: it silences author notifications (which nothing else can short of account-wide preference), @-mentions survive, thread stays open, own comments work, nobody is told, watch subscriptions persist, and it is idempotent (reports state instead of erroring). These details are not present in the annotations and are highly informative.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.