class CLIError(Exception):
    """Base class for all CLI tool errors."""
    pass

class APIError(CLIError):
    """Base class for all API errors."""
    pass

class ValidationError(CLIError):
    """An error that occurs when the user input is invalid."""
    pass

class ConversionError(CLIError):
    """An error that occurs when the converter function cannot convert the input."""
    pass
