Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the burden. It discloses that it queries Google Calendar directly, results are live, and it reflects the next ~20 events, which sets expectations for freshness and scope. It stops short of describing auth requirements or error behavior, but for a read-only list tool these disclosures are meaningful.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.