Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and idempotentHint=true. The description adds meaningful behavioral detail: it explains the output states for connected vs. missing credentials, including the exact fields returned. This helps the agent anticipate results, though it doesn't cover all possible states.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.