custom.php

/**
 * @link http://cfxdesign.com/remove-unused-css-from-wordpress-automatically-with-grunt
 */
function show_sitemap() {
  if(WP_ENV === 'development' && isset($_GET['show_sitemap'])) {
    $the_query = new WP_Query(array('post_type' => 'any', 'posts_per_page' => '-1', 'post_status' => 'publish'));
    $urls = array();
    while($the_query->have_posts()) {
      $the_query->the_post();
      $urls[] = get_permalink();
    }
    die(json_encode($urls));
  }
}
add_action('template_redirect', 'show_sitemap');