# Run PHP in Drupal context
ddev drush php:eval "var_dump(\Drupal::config('my_module.settings')->getRawData());"

# Check if service exists
ddev drush php:eval "var_dump(\Drupal::hasService('my_module.my_service'));"

# Check class autoloading
ddev drush php:eval "class_exists('Drupal\my_module\Service\MyService') ? print 'Found' : print 'Not found';"

# Inspect an entity
ddev drush php:eval "
\$node = \Drupal::entityTypeManager()->getStorage('node')->load(1);
print_r(\$node->toArray());
"

Twig Debugging

Enable in sites/default/services.yml:

parameters:
  twig.config:
    debug: true
    auto_reload: true
    cache: false

Then in templates:

{{ dump(content) }}
{{ dump(node) }}
{{ dump(_context|keys) }}

HTML comments in source will show template suggestions:

<!-- FILE NAME SUGGESTIONS:
  * node--1--full.html.twig
  * node--1.html.twig
  * node--article--full.html.twig
  x node--article.html.twig  ← currently used
  * node--full.html.twig
  * node.html.twig
-->

Devel Module

# Install devel
composer require drupal/devel
ddev drush en devel -y

In PHP:

// Dump and die
dpm($variable);        // Krumo output in message area
ksm($variable);        // Krumo output (devel module)
dvm($variable);        // Var dump

// Krumo (in Twig via Devel)
// {{ devel_dump(node) }}

Cache Debugging

# Clear all caches
ddev drush cr

# Rebuild theme registry only
ddev drush php:eval "\Drupal::service('theme.registry')->reset();"

# Check cache hit for a page (Drupal page cache)
# Look for X-Drupal-Cache: HIT in response headers
curl -I https://my-project.ddev.site/

# Check Big Pipe and render cache
ddev drush state:get drupal.maintenance_mode

Service Container Debugging

# List all services matching a pattern
ddev drush devel:services | grep my_module

# List all services
ddev drush devel:services

# Check container definition
ddev drush php:eval "
\$def = \Drupal::getContainer()->getDefinition('my_module.my_service');
var_dump(\$def);
"

Module/Hook Debugging

# List all enabled modules
ddev drush pm:list --status=enabled

# Check which modules implement a hook
ddev drush php:eval "
\$modules = \Drupal::moduleHandler()->getImplementations('form_alter');
print implode(', ', \$modules);
"

# Check module info
ddev drush pm:info my_module

Common Problems and Solutions

Problem	Solution
Class not found	Check namespace, PSR-4 in .info.yml, run `composer dump-autoload`
Service not found	Check services.yml syntax, run `ddev drush cr`
Template not used	Enable Twig debug, check template suggestions in HTML comments
Hook not firing	Check class is registered in services.yml, verify Hook attribute
Config not saving	Check config schema exists in `config/schema/`
Migration failing	`ddev drush ws` for details, check field mappings

XDebug with DDEV

# Enable XDebug
ddev xdebug on

# Disable XDebug (performance)
ddev xdebug off

# Check XDebug status
ddev xdebug status

Configure IDE (PHPStorm) to listen on port 9003.

drupal-debugging

Drupal Debugging

Drush Log Watching

PHP Inline Debugging