Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden. It does disclose a meaningful trait: the note is durable across restarts and new sessions. It does not, however, describe whether the note overwrites or appends, what authorization is needed, or what the call returns.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.