Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and destructiveHint=false, so the safe-read nature is covered. The description adds important behavioral context: case-insensitivity, returning blocks with page association, and the cached-only limitation. This goes well beyond the annotations and helps set expectations about coverage and results.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.