Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It declares the tool is 'read-only' (safe, non-mutating), 'multi-source' (data aggregation), and 'never a trading directive' (disclaims advice). This provides good behavioral context beyond the input schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.