Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden of disclosing behavior. It only says 'List your recent DM conversations', which is a minimal statement. It does not mention that the operation is read-only, whether there is pagination, how 'recent' is defined, or what the response structure looks like.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.