Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already signal this is not read-only, and the description adds valuable behavioral context: the operation is atomic and creates nothing. This goes beyond what the schema or annotations provide. It leaves some edge semantics unstated, such as how order values are interpreted, but the atomicity and no-creation guarantees are meaningful.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.