Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds valuable non-obvious behavioral context: row ids are account-local, start at 1, are safe to show, and are what other tools expect. This is genuine information beyond what structured annotations and schema provide.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.