Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral disclosure. It reveals that the tool returns the full message thread, that each message has an author field with values 'you' or 'staff', and that 'staff' messages are replies from support. This goes beyond a bare 'read' operation and gives useful behavioral context, though it omits details like error handling or rate limits.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.