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 non-structured value: results are not ranked by an opaque score, the search carries no commercial obligation, and the data/risk profile is R0/PUBLIC, giving the agent a fuller behavioral model than annotations alone.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.