Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and idempotentHint, so the description does not need to cover safety traits. It adds value by specifying that the output is the raw MIME source/full email dump, a key behavioral detail not evident from annotations. It does not mention potential response size or error conditions, but for a read-only getter this is sufficient.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.