Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations exist, so the description carries the burden. It discloses key behaviors: platform-dependent auto-conversion, default save directory (temp), and return of file path or error message. It does not detail authentication needs or potential side effects on server state, but for a download tool this is adequate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.