Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false. Description adds value by specifying the output (titles and IDs) and scope ('all accessible pages'), which goes beyond annotations. Behavior is clearly safe and non-mutative.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.