You can extend the WordPress Debug Bar plugin adding new custom panels to fit your needs; for instance, showing responses from external APIs or webservices, or for other custom features.

// the 'debug_bar_panels' filter it's used by the plugin;
// hook into it to add your custom panel
add_filter( 'debug_bar_panels', 'my_custom_panel_init' );

/**
 * Initialize my custom debug panel
 * @param array $panels Debug bar panels objects
 * @return array Debug bar panels with your custom panels
 */
function my_custom_panel_init( $panels ) {
    // you'll be extending the Debug_Bar_Panel class provided
    // by the plugin
    class Debug_Bar_Custom_Panel extends Debug_Bar_Panel{
        public function init(){
            // you should set at least the title of your custom
            // panel. it'll be used as the tab title
            $this->title( 'Custom Panel' );
        }
        public function render(){
            // build and echo your relevant output
        }
    }
    // add your custom panel
    $panels[] = new Debug_Bar_Custom_Panel();
    return $panels;
}

That’s an extremely simple example. You can check a more complex and complete one by viewing the source of one of the Debug Bar extender plugins, such as the Debug-Bar-Shortcodes GitHub repo.