Drupal Module Development

When to use

• The user wants to implement a Drupal hook such as hook_form_alter or hook_theme in a custom module .module file.
• The user wants to scaffold a new custom Drupal module with an .info.yml manifest and a service or hook.
• The user needs to register a service in a Drupal module .services.yml and inject dependencies into it.

When NOT to use

• Do not build a custom Drupal module when a maintained contrib module on drupal.org already covers the requirement.
• Do not use a module when the task is purely Twig templates, CSS, or JavaScript; that belongs in a Drupal theme.

Core guidance