Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The readOnlyHint annotation already establishes the safety profile, so the description needed to add context such as behavior on a nonexistent id, what fields come back, or whether errors are thrown. It adds no behavioral information beyond what annotations and the name already convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.