Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden and provides useful behavioral details: ownership restriction, return format (JSON with {ok} or {ok: false, error}), and the implicit mutating nature of cancellation. It could mention irreversibility, but for a cancel operation 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.