Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Read-only behavior is already covered by readOnlyHint=true, and the description adds the returned fields (JID, name, subscriber count). It does not disclose pagination, rate limits, or the meaning of idempotentHint=false, but the output schema reduces the need for return-format details.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.