Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and destructiveHint=false, covering the safety profile. The description adds value by explaining the output structure: alternatives are curated and include a one-line 'prefer it when' and a verdict if indexed, giving the agent concrete expectations about what will be returned.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.