Description:

This snippet will allow you to create a meta tag description directly from your post content; what you need to do is apply the code above in your function.php. You should publish max 160 characters as meta tag description.

The Code:

function wpc_meta_tag_desc() {
    global $post;
if (!is_single()) { return; }
    $wpc_meta = strip_tags($post->post_content);
    $wpc_meta = strip_shortcodes($post->post_content);
    $wpc_meta = str_replace(array("\n", "\r", "\t"), ' ', $wpc_meta);
    $wpc_meta = substr($wpc_meta, 0, 160);
    echo "<meta name='description' content='$wpc_meta' />";
}
add_action('wp_head', 'wpc_meta_tag_desc');