Add new menu for custom toolbar items

custom-toolbar.php

<?php
/**
 * Plugin Name: Custom Toolbar
 * Description: Add custom toolbar items in frontent to check page and/or site.
 * Plugin URI:  https://torstenlandsiedel.de
 * Version:     1.0
 * Author:      Torsten Landsiedel
 * Author URI:  http://torstenlandsiedel.de
 * Licence:     GPL 2
 * License URI: http://opensource.org/licenses/GPL-2.0
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly.
}

/**
 * Add toolbar item
 *
 * @param  Object $admin_bar WPAdminBar object.
 */
function add_admin_bar_items( $admin_bar ) {

	// Bail early if no admin.
	if ( ! current_user_can( 'manage_options' ) ) {
		return;
	}

	// Bail early if in admin area.
	if ( is_admin() ) {
		return;
	}

	$menu = array(

		array(
			'id'    => 'quick_menu',
			'title' => 'Quick Menu',
		),

		array(
			'id'     => 'check_w3c',
			'title'  => 'Validate HTML',
			'href'   => 'https://validator.w3.org/nu/?doc=' . rawurlencode( get_permalink() ),
			'parent' => 'quick_menu',
			'meta'   => array(
				'title'  => __( 'Menu Title', 'textdomain' ),
				'target' => '_blank',
			),
		),

	);

	foreach ( $menu as $args ) {
		$admin_bar->add_node( $args );
	}

}

add_action( 'admin_bar_menu', 'add_admin_bar_items', 500 );