Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden and does reasonably well: it discloses the side effect (populating caches), the measurable latency benefit, and that the operation is idempotent. It does not cover auth requirements for api_key, failure modes when caches are already warm, or whether it is a pure local or network operation.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.