Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavior beyond that: results are ranked, each suggestion carries a live result count, demonstrating the autocomplete is backed by real query execution rather than static terms.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.