def get_book_url(tool_name, category):
    """Get the link to the help documentation of the tool.

    Args:
        tool_name (str): The name of the tool.
        category (str): The category of the tool.

    Returns:
        str: The URL to help documentation.
    """
    prefix = "https://jblindsay.github.io/wbt_book/available_tools"
    url = "{}/{}.html#{}".format(prefix, category, tool_name)
    return url