Does the description explain when to use this tool, when not to, or what alternatives exist?
The description clearly implies when to use this tool: whenever the agent needs the current user's own profile data. It doesn't explicitly state when not to use alternatives, but the scoping ('signed-in user') makes it obvious that this is the right choice for self-profile requests, while siblings target other resources (notifications, settings, students, etc.).
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.