How can I get a debug toolbar for my Mezzio application?

Many modern frameworks and applications provide debug toolbars: in-browser toolbars to provide profiling information of the request executed. These can provide invaluable details into application objects, database queries, and more. As an Mezzio user, how can you get similar functionality?

Zend Server Z-Ray

Zend Server ships with a tool called Z-Ray, which provides both a debug toolbar and debug console (for API debugging). Z-Ray is also currently available as a standalone technology preview, and can be added as an extension to an existing PHP installation.

When using Zend Server or the standalone Z-Ray, you do not need to make any changes to your application whatsoever to benefit from it; you simply need to make sure Z-Ray is enabled and/or that you've setup a security token to selectively enable it on-demand. See the Z-Ray documentation for full usage details.


php-middleware/php-debug-bar provides a PSR-15 middleware wrapper around maximebf/php-debugbar, a popular framework-agnostic debug bar for PHP projects.

First, install the middleware in your application:

$ composer require php-middleware/php-debug-bar

This package supplies a config provider, which could be added to your config/config.php when using laminas-config-aggregator or mezzio-config-manager. However, because it should only be enabled in development, we recommend creating a "local" configuration file (e.g., config/autoload/php-debugbar.local.php) when you need to enable it, with the following contents:


use DebugBar\DataCollector\ConfigCollector;
use DebugBar\DebugBar;
use DebugBar\JavascriptRenderer;
use PhpMiddleware\PhpDebugBar\ConfigCollectorFactory;
use PhpMiddleware\PhpDebugBar\ConfigProvider;
use PhpMiddleware\PhpDebugBar\JavascriptRendererFactory;
use PhpMiddleware\PhpDebugBar\PhpDebugBarMiddleware;
use PhpMiddleware\PhpDebugBar\PhpDebugBarMiddlewareFactory;
use PhpMiddleware\PhpDebugBar\StandardDebugBarFactory;
use Psr\Container\ContainerInterface;

return array_merge(ConfigProvider::getConfig(), [
    'dependencies' => [
        'factories' => [
            PhpDebugBarMiddleware::class => PhpDebugBarMiddlewareFactory::class,
            ConfigCollector::class => ConfigCollectorFactory::class,
            ConfigProvider::class => function(ContainerInterface $container) {
                return $container->get('config');
            DebugBar::class => StandardDebugBarFactory::class,
            JavascriptRenderer::class => JavascriptRendererFactory::class,

In addition, ensure the PSR-17 HTTP message factory interfaces are registered in your container. For example, when using Diactoros as your PSR-7 HTTP message interfaces implementation, you can define the following:

use Laminas\Diactoros\ResponseFactory;
use Laminas\Diactoros\StreamFactory;
use Psr\Http\Message\ResponseFactoryInterface;
use Psr\Http\Message\StreamFactoryInterface;

return [
    'dependencies' => [
        'invokables' => [
            ResponseFactoryInterface::class => ResponseFactory::class,
            StreamFactoryInterface::class   => StreamFactory::class
        // ...

Starting with Diactoros 2.3.0, you can register the above PSR-17 services by adding an entry for \Laminas\Diactoros\ConfigProvider::class to your config/config.php file, if it is not added for you during installation.

Finally, add the PhpDebugBarMiddleware class to the pipeline in config/pipeline.php after piping the ErrorHandler class:

if (! empty($container->get('config')['debug'])) {

Usage in a Request Handler

You can add messages to the debug bar within request handlers and middleware. As an example, in your src/App/Handler/HomePageHandler.php, you might do the following:

namespace App\Handler;
use Psr\Http\Server\RequestHandlerInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Message\ResponseInterface;
use Mezzio\Template\TemplateRendererInterface;
use Laminas\Diactoros\Response\HtmlResponse;
use DebugBar\DebugBar;

class HomePageHandler implements RequestHandlerInterface
    /** @var TemplateRendererInterface */
    public $template;

    /** @var DebugBar */
    public $debugBar;

    public function __construct(TemplateRendererInterface $template, DebugBar $debugBar)
        $this->template = $template;
        $this->debugBar = $debugBar;

    public function handle(ServerRequestInterface $request) : ResponseInterface
        $this->debugBar['messages']->addMessage('Hello World!');
        return new HtmlResponse($this->template->render('user::home-page'));

Only use in development

Remember to enable PhpMiddleware\PhpDebugBar\ConfigProvider only in your development environments, and to remove references to the DebugBar class in production!

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