Debug WordPress rewrite rules

functions.php

<?php
function debug_rewrite_rules() {
    global $wp, $template, $wp_rewrite;

    echo '<pre>';
    echo 'Request: ';
    echo empty($wp->request) ? "None" : esc_html($wp->request) . PHP_EOL;
    echo 'Matched Rewrite Rule: ';
    echo empty($wp->matched_rule) ? None : esc_html($wp->matched_rule) . PHP_EOL;
    echo 'Matched Rewrite Query: ';
    echo empty($wp->matched_query) ? "None" : esc_html($wp->matched_query) . PHP_EOL;
    echo 'Loaded Template: ';
    echo basename($template);
    echo '</pre>' . PHP_EOL;

    echo '<pre>';
    print_r($wp_rewrite->rules);
    echo '</pre>';
}

add_action( 'wp_head', 'debug_rewrite_rules' );