Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool read-only, idempotent, and non-destructive; the description adds concrete behavioral context by stating the unfiltered scope ('every data source') and the exact fields returned. This exceeds what annotations alone convey, though it omits richer details such as pagination or data freshness, which are partly covered by the existing output schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.