Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover the safety profile (readOnly, idempotent=false, destructive=false, openWorld=false), and the description adds real behavioral context: it blocks, sends no interim notices, and exits on completion, failure, or timeout. It stops short of saying what the caller observes on timeout/failure or what the maximum wait is.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.