Custom Drush command for managing Twig debugging and CSS/JS aggregation

The custom Drush command theme:dev makes it easy to switch between development and production settings on your Drupal site. With a single command, you can toggle CSS/JS aggregation and Twig debugging — two settings that are often adjusted while debugging.

• on mode turns off aggregation and enables Twig debugging, which is perfect while you're actively developing or theming your site.

• off mode turns on aggregation (for better performance) and turns off Twig debugging. Use this when you're preparing for production.

Steps to add custom theme:dev Drush command:

1. Create a drush directory in the Drupal project root, add a Commands sub-directory inside, and finally a ThemeDevCommands.php file for this structure:
   

   drupal
   ├── composer.json
   ├── composer.lock
   ├── drush
   │   └── Commands
   │       └── ThemeDevCommands.php
   ├── vendor
   └── web
   

2. Add this inside ThemeDevCommands.php:
    

   <?php
   
   declare(strict_types=1);
   
   namespace Drush\Commands;
   
   use Drush\Attributes as CLI;
   use Drush\Commands\DrushCommands;
   use Drupal\Core\KeyValueStore\KeyValueFactoryInterface;
   use Drupal\Core\Config\ConfigFactoryInterface;
   use Symfony\Component\DependencyInjection\ContainerInterface;
   
   final class ThemeDevCommands extends DrushCommands
   {
       const DEV = 'theme:dev';
   
       public function __construct(
           protected KeyValueFactoryInterface $keyValueFactory,
           protected ConfigFactoryInterface $configFactory
       ) {
       }
   
       public static function create(ContainerInterface $container): self
       {
           return new self(
               $container->get('keyvalue'),
               $container->get('config.factory')
           );
       }
   
       /**
        * Toggle Twig development and cache aggregation settings.
        *
        * When enabled:
        * - Disables render cache, dynamic page cache, and page cache.
        * - Enables Twig debug mode (e.g., `dump()` function, template suggestions).
        * - Disables Twig cache (templates always recompiled).
        * - Disables CSS and JS aggregation.
        *
        * When disabled, restores default performance-oriented settings.
        *
        * Clears all Drupal caches to apply changes immediately.
        */
       #[CLI\Command(name: self::DEV, aliases: ['thdev'])]
       #[CLI\Argument(name: 'mode', description: '"on" or "off"', suggestedValues: ['on', 'off'])]
       #[CLI\Usage(name: 'drush theme:dev on', description: 'Disables CSS/JS aggregation and enables Twig debug settings.')]
       #[CLI\Usage(name: 'drush theme:dev off', description: 'Enables CSS/JS aggregation and disables Twig debug settings.')]
       public function toggleDevMode(string $mode): void
       {
           if (!in_array($mode, ['on', 'off'])) {
               throw new \InvalidArgumentException("Invalid mode. Use 'on' or 'off'.");
           }
   
           $devMode = $mode === 'on';
   
           $this->keyValueFactory->get('development_settings')->setMultiple([
               'disable_rendered_output_cache_bins' => $devMode,
               'twig_debug' => $devMode,
               'twig_cache_disable' => $devMode,
           ]);
   
           $this->configFactory->getEditable('system.performance')
               ->set('css.preprocess', !$devMode)
               ->set('js.preprocess', !$devMode)
               ->save();
   
           drupal_flush_all_caches();
   
           $this->logger()->success(sprintf(
               'Developer mode %s: CSS/JS aggregation %s, Twig debug settings %s.',
               $mode === 'on' ? 'enabled' : 'disabled',
               $devMode ? 'disabled' : 'enabled',
               $devMode ? 'enabled' : 'disabled'
           ));
       }
   }
   

Disable aggregation and enable Twig debugging:

drush theme:dev on

Enable aggregation and disable Twig debugging:

drush theme:dev off

There's even an alias:

drush thdev on
drush thdev off

Built by @keshav patel, see #3342678: Easy way to bypass caching and aggregation with Drush or settings.php and Add Drush command to toggle Twig debugging and CSS/JS aggregation #6267.