Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), so the bar is lower. The description still adds real behavior beyond them: it syncs through macOS Reminders, it refuses on ambiguous list names rather than guessing, and it names the accounts it read. The refusal-on-ambiguity behavior is exactly the kind of thing an agent must anticipate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.