Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is known. The description adds behavioral context by specifying the two response cases (all connected vs. missing credentials) and the URLs returned, which is valuable for an agent to interpret the response. It doesn't cover every edge case but sufficiently discloses behavior beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.