Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=false), and the description adds meaningful context beyond them: results are restricted to the caller's own content and it must not be used to enumerate other users' data. It stops short of disclosing result-volume, ranking, or pagination behaviour, so it is good rather than rich.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.