Create a Custom XML Sitemap in WordPress Without Plugins

Code

<?php
// Hook into the 'init' action to register the sitemap rewrite rule
add_action('init', 'wp_dudecom_add_sitemap_rewrite_rule');

function wp_dudecom_add_sitemap_rewrite_rule() {
    add_rewrite_rule('^custom-sitemap\.xml$', 'index.php?custom_sitemap=1', 'top');
}

// Hook into 'query_vars' to add custom query variable
add_filter('query_vars', 'wp_dudecom_add_query_vars');

function wp_dudecom_add_query_vars($vars) {
    $vars[] = 'custom_sitemap';
    return $vars;
}

// Hook into 'template_redirect' to generate the sitemap
add_action('template_redirect', 'wp_dudecom_generate_custom_sitemap');

function wp_dudecom_generate_custom_sitemap() {
    if (get_query_var('custom_sitemap')) {
        header('Content-Type: application/xml; charset=utf-8');
        
        $posts = get_posts(array(
            'post_type' => 'post',
            'post_status' => 'publish',
            'numberposts' => -1
        ));
        
        $sitemap = '<?xml version="1.0" encoding="UTF-8"?>';
        $sitemap .= '<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">';
        
        foreach ($posts as $post) {
            $sitemap .= '<url>';
            $sitemap .= '<loc>' . esc_url(get_permalink($post->ID)) . '</loc>';
            $sitemap .= '<lastmod>' . esc_html(get_the_modified_date('c', $post->ID)) . '</lastmod>';
            $sitemap .= '<changefreq>weekly</changefreq>';
            $sitemap .= '<priority>0.8</priority>';
            $sitemap .= '</url>';
        }
        
        // Add custom URLs
        $custom_urls = array(
            home_url('/custom-page-1/'),
            home_url('/custom-page-2/')
        );
        
        foreach ($custom_urls as $url) {
            $sitemap .= '<url>';
            $sitemap .= '<loc>' . esc_url($url) . '</loc>';
            $sitemap .= '<changefreq>monthly</changefreq>';
            $sitemap .= '<priority>0.5</priority>';
            $sitemap .= '</url>';
        }
        
        $sitemap .= '</urlset>';
        
        echo $sitemap;
        exit;
    }
}

// Hook into 'after_switch_theme' to flush rewrite rules
add_action('after_switch_theme', 'wp_dudecom_flush_rewrite_rules');

function wp_dudecom_flush_rewrite_rules() {
    flush_rewrite_rules();
}
?>