Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
With no output schema, the description compensates by naming the fields returned (weekday hours, weekly total, default flag), which is exactly the information an agent needs. It could still say whether the list can be empty or how ordering works, but for a simple parameterless list tool this is close to complete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.