Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish read-only, idempotent, non-destructive behavior. The description adds meaningful context beyond annotations: license source and check date, data freshness, directory link, suggested citation, and exact consent text required before an introduction.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.