Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden of explaining behavior. It does reveal an important trait: the old fact is not wiped but retained in history. It does not clarify the resulting status of the old memory, whether the new memory must already exist, or whether the operation is reversible.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.