Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
An output schema exists, so return values need not be described. However, for a 'calculates costs' tool whose only parameter is a model name, the description leaves the critical question unanswered: where do the token counts come from, and which model identifiers are accepted? An agent cannot reliably construct a call from this.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.