Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly/destructive/idempotent status, so the safety profile is covered. The description adds non-obvious behavior beyond the annotations: a 5-minute signed URL and the redirect-vs-JSON response mode, which are exactly the operational details an agent needs. Error behavior (missing file, expired URL handling) is not covered, keeping it below 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.