Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate a read-only, non-destructive operation, and the description adds useful behavioral detail beyond that: results are ordered oldest first and include each comment's id, author, and edited status. This is meaningful context for an agent deciding whether the returned data will satisfy the user's request.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.