Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden. 'List all available' implies a read-only enumeration with no side effects, which is a reasonable inference, but it says nothing about return shape, ordering, pagination, or whether the guides are static versus game-state dependent.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.