Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations (which only declare it as a safe, idempotent read), the description adds pagination behavior (50 per page, next_cursor/has_more contract), the billing status ('Not billed'), and a concrete rate limit shared across all tools. These are operational facts an agent cannot derive from the schema or annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.