Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations present, the description carries the full burden of disclosing behavior. It reveals the mutating nature (add/remove) but does not explain side effects, such as whether duplicate members are handled, what happens if the container does not exist, whether changes are reversible, or whether any permissions are required.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.