meta

function add_my_meta() {
if(is_single()) :
$posttags = get_the_tags();
if ($posttags) {
$tag_names = '';
foreach($posttags as $tag) {
    $tag_names .= $tag->name . ',';
}
?>
<meta name="keywords" content="<?php echo rtrim($tag_names, ','); ?>"/>
<?php } ?>
<meta name="description" content="<?php echo wp_strip_all_tags(get_the_excerpt(), true); ?>"/>
<?php endif;
}
add_action('wp_head', 'add_my_meta');