Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple deletion tool with one parameter and no output schema, the description covers the purpose, usage conditions, and relationship to siblings. It doesn't detail error handling for missing keys, but the idempotent annotation partially addresses that, and such detail is not essential for a basic delete.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.