Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, openWorldHint, and idempotentHint, so the safety profile is known. The description adds behavioral transparency by stating it is asynchronous and requires async:true, and it reveals the data sources and output format (sustainability impact scores), which go beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.