Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare destructiveHint=true and non-idempotent, so the safety profile is covered. The description adds real value beyond that: it names the target state (done column), discloses the return value (updated board), and specifies the ambiguity-handling policy of asking the user first, which is behavioral guidance not present in annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.