Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool as non-read-only, open-world, non-idempotent, and destructive; the description adds crucial context beyond that. It explains what mode full does, that it rewrites every record without duplicates to repair failed records, that it takes longer, that confirmation is required, and that a sync starts at most once every 15 minutes per integration.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.