Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. It usefully discloses one trait: memory is never stored automatically, only on explicit choice. However it says nothing about permissions required, persistence/retrieval behavior, mutability of a stored memory, or what the write returns.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.