Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple single-parameter read tool, the description is complete. It states what is fetched, by what identifier, that it is read-only, and that PHI sensitivity applies. No output schema exists, but the description sufficiently implies the return payload without needing to explain it.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.