Drupal 8, 9, & 10 Theme Dev Config

localdev.services.yml

# Should go in /sites/localdev.services.yml, or wherever the container_yamls setting in settings.local.php is set to look for it

# Local development services.
#
# To activate this feature, follow the instructions at the top of the
# 'example.settings.local.php' file, which sits next to this file.
parameters:
  http.response.debug_cacheability_headers: true
  twig.config:
    debug: true
    auto_reload: true
services:
  cache.backend.null:
    class: Drupal\Core\Cache\NullBackendFactory

settings.local.php

<?php

$settings['container_yamls'][] = DRUPAL_ROOT . '/sites/localdev.services.yml';
$config['system.logging']['error_level'] = 'verbose';
$config['system.performance']['css']['preprocess'] = FALSE;
$config['system.performance']['js']['preprocess'] = FALSE;
$settings['cache']['bins']['render'] = 'cache.backend.null';
$settings['cache']['bins']['dynamic_page_cache'] = 'cache.backend.null';
$settings['rebuild_access'] = TRUE;
$settings['skip_permissions_hardening'] = TRUE;

// Whatever other stuff, like DB and other settings