Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate a safe, read-only, idempotent operation. The description adds valuable behavioral context: it returns MATCH or DRIFT node by node, and nodes that cannot be re-observed are deferred rather than counted as drift. This goes beyond basic safety and explains edge-case handling.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.