Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only and idempotent behavior, so the bar is lower. The description adds meaningful context by specifying the exact weighting scheme, clarifying that this is a local checksum validation and not format-only or database verification.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.