Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Without annotations, the description carries the full burden. It discloses the data source (open-meteo), geographic scope (Berlin, Frankfurt, Munich), time horizon (next 3 days), and threshold flags (28°C and 32°C), making behavior transparent. It doesn't mention potential latency or failure modes, but for a parameterless lookup this is adequate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.