Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only and idempotent safety. The description adds valuable behavioral detail beyond that: the batch costs one upstream request, missing IDs are reported per-id in 'unresolved' rather than failing the batch, and the call fails only when nothing resolves. This gives the agent clear expectations for error handling and cost, exceeding the baseline provided by annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.