Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true, idempotentHint=false); the description adds non-obvious behavior by telling the agent this kicks off a runner job (async, not a synchronous result) and that it has no outreach side effect. It stops short of stating whether the job can be polled, retried, or what account permission it needs.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.