Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and openWorldHint. The description adds meaningful behavior beyond that: it is a cursor-driven delta feed returning only items new since the last read, and it signals a poll cadence/rate expectation ('suggested interval'). It stops short of describing pagination, ordering, or response shape.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.