Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
With no output schema present, the description usefully enumerates what the response contains (plan tier, credits, limits), which largely substitutes for a return-value spec. It is complete enough for an agent to call correctly, though it does not state the response format.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.