Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given no output schema and no parameters, the description lists the exact fields returned (source, date, licence, citation), which is sufficient for an agent to understand the result. It could mention that the tool is read-only or that the dataset is fixed, but overall it is complete for this simple tool.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.