Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple one-parameter tool with annotations and no output schema, the description is complete enough. It covers purpose, usage, parameter, and related tools. The idempotentHint annotation addresses behavior for missing keys, so the description doesn't need to explain that. Some might expect a note on return value, but that's not critical here.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.