Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose two useful traits: results come from a 'local session cache' and the result set is uncapped. However, it omits the practical consequences of an unbounded fetch (volume, performance, pagination) and whether the cache can be stale relative to server state.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.