What’s slowing down your WordPress page? Try adding this to your functions.php to see your pain points in red. Remember to change the IP address in one_of_us() to keep test results private:

// Performance testing
add_action('muplugins_loaded', 'pj_time');
add_action('registered_taxonomy', 'pj_time');
add_action('registered_post_type', 'pj_time');
add_action('plugins_loaded', 'pj_time');
add_action('sanitize_comment_cookies', 'pj_time');
add_action('setup_theme', 'pj_time');
add_action('load_textdomain', 'pj_time');
add_action('after_setup_theme', 'pj_time');
add_action('set_current_user', 'pj_time');
add_action('init', 'pj_time');
add_action('widgets_init', 'pj_time');
add_action('register_sidebar', 'pj_time');
add_action('wp_register_sidebar_widget', 'pj_time');
add_action('wp_default_scripts', 'pj_time');
add_action('wp_default_styles', 'pj_time');
add_action('admin_bar_init', 'pj_time');
add_action('add_admin_bar_menus', 'pj_time');
add_action('wp_loaded', 'pj_time');
add_action('parse_request', 'pj_time');
add_action('send_headers', 'pj_time');
add_action('parse_query', 'pj_time');
add_action('pre_get_posts', 'pj_time');
add_action('posts_selection', 'pj_time');
add_action('wp', 'pj_time');
add_action('template_redirect', 'pj_time');
add_action('wp_loaded', 'pj_time');
add_action('wp_head', 'pj_time');
add_action('wp_footer', 'pj_time');

// More hooks here http://codex.wordpress.org/Plugin_API/Action_Reference
// Check your theme's documentation, it may have more hooks to test.

 
function pj_time () {
  if (one_of_us()) {
    $old_time = $GLOBALS["performance_timer"];
    $GLOBALS["performance_timer"] = microtime(true);
    $new_time = $GLOBALS["performance_timer"];
    $diff = round($new_time - $old_time, 4);
    // The < 100 seconds just hides the ugly starting time hook
    // Increase .01 to .1 seconds to see only the worst pain points.
    if (($diff > 0.01) && ($diff < 100)) {
      echo '<div style="color:red;">';
      echo 'Test time of '. current_filter() .': '. $diff .'s. ';
      echo '</div>';
    }
  }
}

 
function one_of_us() {
  if ($_SERVER['REMOTE_ADDR']=="x.x.x.x") return true;
  return false;
}

 

If there’s a slow spot, the output will look something like this: Test time of parse_query: 0.123s. The time is measured from hook to hook. So adding more hooks helps you pinpoint what’s slow.