Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false, which aligns with the mutation described. The description adds a small precondition ('existing contact list') but does not disclose behavior such as duplicate handling, idempotency, or repercussions for invalid contact IDs. With annotations covering the basic mutation/destruction profile, this is acceptable but not rich.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.