Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish readOnly/non-destructive/non-open-world, so the safety profile is covered. The description adds return-shape behavior: a cap of 10 results and the per-result id/title/URL fields, plus the fact that the text block mirrors the JSON as a string. That is useful beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.