Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and destructiveHint=false. The description adds genuinely useful behavior: the four possible status values and the error semantics (404 for missing/other-account websites, 400 for a non-UUID id), which an agent cannot infer from annotations or schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.