Find All Functions Hooking Into A Filter/Action in WordPress

Filter Inspector

<?php
/*
Plugin Name: Find Functions Hooking Into Filters/Actions
Description: Find All Functions Hooking Into A Filter/Action in WordPress
Author:      Jon Bishop
Author URI:  http://www.jonbishop.com/
Version:     1.0
*/

function amp_find_filters($filter_name) {
    global $wp_filter;
    echo 'Filter: ' . $filter_name . '<br>';
    if (isset($wp_filter[$filter_name])) {
        foreach ($wp_filter[$filter_name] as $priority => $functions) {
            foreach ($functions as $function => $args) {
                if (is_object($args['function'][0])) {
                    $refClass = new ReflectionClass($args['function'][0]);
                    $refFunc = $refClass->getMethod($args['function'][1]);
                    echo 'class name: ' . $refClass->getName() . '<br>';
                    echo 'method name: ' . $args['function'][1] . '<br>';
                } else {
                    $refFunc = new ReflectionFunction($args['function']);
                    echo 'function name: ' . $args['function'] . '<br>';
                }
                echo 'file name: ' . $refFunc->getFileName() . '<br>';
                echo 'start line: ' . $refFunc->getStartLine() . '<br>';
                echo '<hr>';
                $refFunc = null;
            }
        }
    }
}
 
// Usage
amp_find_filters('wp_footer');