Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden and delivers almost nothing: it does not say whether this frees memory only or also deletes persistent data, what happens if the name is unknown, or whether it is idempotent. 'From memory' is the only behavioral clue.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.