Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It discloses that 'No API key required' (auth requirement), returns active sites only, and provides a max limit of 500 beyond the schema. It does not mention rate limits or error behavior, but the added context about API key and constraints is meaningful.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.