Add Twig Debug extension in Silex

app.php

<?php
//and in your application add:
$app['twig'] = $app->share($app->extend('twig', function($twig, $app) {
    $twig->addExtension(new \Twig_Extensions_Extension_Debug());
    return $twig;
}));

composer.json

{
//..
"autoload": {
        "psr-0": { "Twig_Extensions_": "vendor/twig/extensions/lib/" }
    },
//..
}