Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given the tool has 5 parameters, an output schema, and strong annotations, the description covers all meaningful usage variations: area_name+state_code, FIPS expansion, entity_id omission, and year default. It does not need to explain return values because the output schema exists, and the safety profile is supplied by annotations.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.