Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only declare readOnlyHint=false, so the description carries the behavioral disclosure burden. It does well by warning that 'without a key, documents will not ingest' and noting the cost implication ('$0 to the platform — you use your own key'). This is valuable beyond the schema, although it does not cover all side effects (e.g., reversibility).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.