Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple 3-parameter read tool, the description is fairly complete: purpose, data source, and parameter semantics are covered. An output schema exists, so return values don't need description. It could mention edge cases or availability, but these are not critical for this tool.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.