Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false and destructiveHint=false, so the mutation profile is covered structurally. The description usefully discloses the 'all' sentinel behavior, which the schema does not, but says nothing about what happens if the key is not currently held or about failure behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.