Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
Given that the tool has no output schema, the description reasonably outlines what the user will get: validation, formatting, and analysis of country, format validity, and mobile status. It also notes no external API and cost. While it lacks exact output structure, it is sufficient for a simple one-param utility.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.