Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive behavior, so the bar is lower, and the description still adds real context the annotations don't: results are stored snapshots rather than a live feed, and they preserve attribution and original links. That snapshot-vs-live distinction materially affects how an agent should interpret recency.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.