Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Without annotations, the description carries the full burden. It explains the exact matching method (id_field or array position) and that comparison is structural, not topological. It also details the output format. However, it does not mention performance, error handling, or input size limits.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.