my debug mu-plugin. only use this on localhost.

gistfile1.php

<?php
/**
 * Plugin Name: Debug-ing
 * Plugin URI: http://shellcreeper.com/
 * Description: just for debug on localhost.
 * Version: 0.1.0
 * Author: David Chandra Purnama
 * Author URI: http://shellcreeper.com/
 */

//add_action('admin_footer','capsule_print_data');
//add_action('wp_footer','capsule_print_data');


/* data to display */
function capsule_print_data(){
  $testing = WP_CONTENT_DIR;
	ccdd( $testing, 'WP_CONTENT_DIR' );
}



//add_action( 'admin_notices', 'capsule_print_notice_admin_pagehook' );

/**
 * Print Admin Hook
 */
function capsule_print_notice_admin_pagehook(){
	global $hook_suffix, $pagenow;
	if( ! current_user_can( 'manage_options') ) return;
	?>
	<div class="error">
		<p>$hook_suffix: <code><?php echo $hook_suffix; ?></code> $pagenow: <code><?php echo $pagenow; ?></code> </p>
	</div>
	<?php
}


/**
 * Preety Debug Data
 * @link http://chrisbratlien.com/prettier-php-debug-messages-continued/
 */
function ccdd( $obj, $label = '' ) {  

	$data = json_encode(print_r($obj,true));
	?>
	<style type="text/css">
		#bsdLogger {
		position: inherit;
		bottom:0;
		border: 3px solid #ffa601;
		padding: 6px;
		background: white;
		color: #444;
		z-index: 999;
		font-size: 1.25em;
		width: 980px;
		overflow: scroll;
		margin: 50px auto 0 auto;
		}
	</style>    
	<script type="text/javascript">
	var doStuff = function(){
		var obj = <?php echo $data; ?>;
		var logger = document.getElementById('bsdLogger');
		if (!logger) {
			logger = document.createElement('div');
			logger.id = 'bsdLogger';
			document.body.appendChild(logger);
		}
		////console.log(obj);
		var pre = document.createElement('pre');
		var h2 = document.createElement('h2');
		pre.innerHTML = obj;

		h2.innerHTML = '<?php echo addslashes($label); ?>';
		logger.appendChild(h2);
		logger.appendChild(pre);      
	};
	window.addEventListener ("DOMContentLoaded", doStuff, false);

	</script>
	<?php
}