WordPress - Custom post with custom permalink (slug)

functions.php

<?php 
add_action( 'init', 'register_new_post_type' );
function register_new_post_type(){
    $args = array(
        'label' => 'Post title',
        'show_ui' => true,
        'public' => true,
        'hierarchical' => true,
        'has_archive' => true,
        'supports' => array( 'title' ),
        'rewrite' => array(
            'slug' => 'new_post_type',
            'with_front' => false
        )
    );
    register_post_type( 'new_post_type', $args );
}