Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With only readOnlyHint=true supplied, the description adds real behavioral context: the output is a single combined plan, addresses are non-derivable external inputs, and a wrong address fails silently ('claims nothing rather than failing loudly') — a meaningful hazard worth surfacing. It does not discuss how the plan is returned or sequenced, but the output schema can carry that.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.