Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover read-only, idempotent, non-destructive, and open-world. The description adds real behavioral context beyond them: page size (50 per call), that results are ranked by votes and ranks can shift between calls, and that only public data is returned with no contact details. Rate limits aren't mentioned, but the ranking volatility and pagination details are valuable.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.