Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent behavior. The description adds algorithmic transparency by specifying the exact checksum calculation (odd positions x1, even positions x3), making it clear the tool only mathematically validates the barcode rather than confirming real-world product existence.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.