Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool as destructive, non-read-only, and idempotent. The description adds valuable behavior beyond those flags: the stop is cooperative, not immediate, and occurs on the browser extension's next heartbeat, usually within ~12s, after which the run is finalized. This is exactly the kind of behavioral context that helps an agent set expectations correctly.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.