Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, so the description is not required to state safety. It adds the behavior of defaulting to the latest round when round is omitted, which is useful. However, it does not disclose anything about error conditions or what happens if no report exists for a round, but given the read-only nature and simplicity, a 3 is appropriate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.