Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, openWorldHint=true, destructiveHint=false, so safety and reach are covered elsewhere. The description adds value by disclosing the shape of the response (stage, picks, mediaId, postIds), which matters because no output schema exists, but it says nothing about failure modes or what values 'stage' can take.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.