Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, destructiveHint, and idempotentHint. The description adds meaningful behavioral details: it returns only the 50 most recent versions and includes specific fields (dist-tags, deprecation status, total count). This goes beyond the annotations to set user expectations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.