Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and idempotentHint. The description adds valuable behavioral details: it specifies the exact response in connected state (authenticated:true, empty pending[]) and in missing-credentials state (connect_url and per-install URLs). This goes beyond the annotations and helps the agent anticipate outcomes.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.