Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already confirm read-only/idempotent behavior; description adds that the search is by substring and returns specific entries, not full documents. It also warns that valid slugs come from docs/search_docs, adding practical behavioral context. No contradiction with annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.