Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses the state machine (idle/running/success/failed/timeout/cancelled) and the key operator behavior (prompt the user to finish captcha/scan in the popup browser), which is genuinely useful. It does not say the call is read-only/non-mutating, whether polling is rate-limited, or what an agent should do on timeout/failed.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.