Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, destructiveHint=false. The description adds value by detailing the information content (19 sites, fees, passes, etc.), which is behavioral in terms of expected output.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.