Change tooltip in tag cloud

How to change tag tooltip to tag Description?

I tried and my code is mentioned below.

function title_text( $description ) {
    return sprintf( _n('%s topic', '%s', $description), $description );
}

wp_tag_cloud( array( 'topic_count_text_callback' => 'title_text') );

This is not working. Can any one please check this code and find me a correct solution?

The argument topic_count_text_callback cannot do what you need, because it doesn’t get the term ID and the taxonomy as arguments. This should be fixed in core. I think I will write a patch for that later.

Update: I have written a patch for Ticket #21198. The milestone is 3.6, so the following answer will be out of date eventually. I will update this post then.

But not all hope is lost. We can filter the generated markup on wp_tag_cloud, run a regex on that and extract the term ID from the class attribute and the taxonomy from the second parameter $args. Then we use the term ID and the taxonomy to get the term description and replace the original title attribute.

add_filter(
    'wp_tag_cloud', # filter name
    array ( 'WPSE_78426_Tag_Cloud_Filter', 'filter_cloud' ), # callback
    10, # priority
    2   # number of arguments
);

/**
 * Replace title attribut in a tag cloud with term description
 *
 * @author toscho http://toscho.de
 */
class WPSE_78426_Tag_Cloud_Filter
{
    /**
     * Current taxonomy
     *
     * @type string
     */
    protected static $taxonomy = 'post_tag';

    /**
     * Register current taxonomy and catch term id per regex.
     *
     * @wp-hook wp_tag_cloud
     * @uses    preg_callback()
     * @param   string $tagcloud Tab cloud markup
     * @param   array  $args Original arguments for wp_tag_cloud() call
     * @return  string Changed markup
     */
    public static function filter_cloud( $tagcloud, $args )
    {
        // store the taxonomy for later use in our callback
        self::$taxonomy = $args['taxonomy'];

        return preg_replace_callback(
            '~class=\'tag-link-(\d+)\' title=\'([^\']+)\'~m',
            array ( __CLASS__, 'preg_callback' ),
            $tagcloud
        );
    }

    /**
     * Replace content of title attribute.
     *
     * @param array $matches
     *        $matches[0] = complete matched string,
     *        $matches[1] = term id,
     *        $matches[2] = original content of title attribute
     * @return string
     */
    protected static function preg_callback( $matches )
    {
        $term_id = $matches[1];
        // get term description
        $desc = term_description( $term_id, self::$taxonomy );
        // remove HTML
        $desc = wp_strip_all_tags( $desc, TRUE );
        // escape unsafe chacters
        $desc = esc_attr( $desc );

        // rebuild the attributes, keep delimiters (') intact
        // for other filters
        return "class="tag-link-$term_id" title="$desc"";
    }
}

Result