Single Directory Components in Drupal

A Drupal single directory component (SDC) is Drupal's way of packaging the markup, metadata, styles, and behavior for a UI element in one self-contained folder inside a theme or module. This structure helps front-end developers and site builders keep all related files together for easier theming and reuse. A Drupal single directory component directory must be located in a specific place and its files named with a particular convention so that the system can discover it and use its assets.

In this tutorial, we'll:

• Show where Drupal discovers single directory components in your codebase.
• Explain the naming and organization conventions for Drupal single directory component directories and files.
• Outline key files for a component—both required and optional.

By the end of this tutorial, you'll be able to identify an SDC directory in a Drupal module or theme and know exactly what you're looking at.

In this tutorial, you’ll create and render a simple single directory component (SDC) in Drupal. You’ll set up the required files, call the component from a template, and confirm that Drupal renders it with its styles automatically attached.

By following along, you will:

• Scaffold the files for a basic card component.
• Reference the component in a node template.
• See how Drupal renders the component’s HTML and CSS together.

When you’re done, you’ll have a complete working example of a Drupal single directory component.

Props and slots are the two ways that data can be provided to a single directory component (SDC). They are part of a component's schema definition, and are used to determine the names of variables passed to a component's template file. Props pass structured, validated data into a component, while slots allow us to inject flexible content such as HTML or nested components. Understanding when and how to use each ensures you can build reusable and adaptable components.

In this tutorial, we'll:

• Learn what props and slots are, and how they differ.
• Discuss how using one or the other impacts the developer experience and use of your components in a UI.
• Practice deciding when to use each for component design.

By the end of this tutorial, you'll know how to choose between props and slots when building components.

The component YAML file, with the suffix .component.yml, is the heart of every Drupal single directory component (SDC). This file describes how consumers can pass data (props) and nest content (slots) into the component. Similar to a PHP interface, the schema defined in a .component.yml file acts as a contract that tells consumers (both developers and low-code tools) what data a component accepts and what shape it expects.

In this tutorial, you’ll learn what each key in a component's YAML file does. You’ll see how the file names the component, describes its API, and helps low-code tools validate and expose your component. Then we’ll create a new card component with a card.component.yml file.

By following along, you will:

• Reinforce your understanding of where a Drupal component's YAML file lives and why it matters.
• Break down each top-level key—$schema, name, description, props, and slots.
• Learn more about what you can put into a .component.yml file.

By the end of this tutorial, you’ll have a discoverable card.component.yml file for a new card SDC and a mental model for how Drupal uses it.

Drupal single directory components use Twig template files to define their HTML markup and how the values of props and slots are displayed. To discover available props and slots, read the component’s .component.yml file. When working with slots, you’ll often choose between rendering a slot as a Twig block ({% block %}) or interpolating a variable directly ({{ variable }}).

In this tutorial, you’ll:

• Add a card.twig file to an existing component directory.
• Read the associated card.component.yml schema to identify props and slots you can work with.
• Render props and slots wrapped in custom HTML markup.

By the end of this tutorial, you’ll be able to connect a Twig template to any SDC and render the props and slots passed into the component.

One of the benefits of using Drupal single directory components is that Drupal automatically builds and attaches an asset library whenever it is used. Adding CSS styles and JavaScript interactivity to a single directory component (SDC) is as simple as dropping component-name.css and component-name.js files into the root directory of the component. Drupal detects these files, creates an asset library, and attaches it when the component is rendered. This means when you want to add additional CSS or JavaScript assets, you will override the asset library created for your component instead of defining a new one.

In this tutorial, we will:

• Add component-scoped CSS and JavaScript files.
• Learn how to override a component's existing asset library to add additional assets.
• Discuss how to integrate common front-end asset build tools (Gulp, Webpack, Vite, etc.) while working with Drupal single directory components.

By the end of this tutorial, you'll be able to attach CSS and JavaScript assets to an SDC and validate that they load only when the component is in use.

As a module developer, you output themed content from your module in the form of renderable arrays. When doing so, you can make use of single directory components (SDCs) by using the #type => 'component' render element type. This allows modules to dynamically select and configure a component based on configuration or specific PHP logic. You'll use this as the return value of a controller, or a configurable plugin related to display building, like custom blocks or field formatters. As an example, we'll author a custom block plugin that loads a specific node and outputs it using the card SDC we defined in a previous tutorial. We'll build a render array that supplies the values for the component's props and slots, and add some caching logic to the output.

In this tutorial, we will:

• Build a render array that targets an SDC via the #component property.
• Pass data into the component's props and slots, and demonstrate optional #propsAlter and #slotsAlter callbacks.
• Validate the output and cache it properly.

By the end of this tutorial, you'll be able to render any SDC via a module's PHP code using a well-structured and cache-friendly render array.

Learn how to embed a Drupal single directory component (SDC) in a Twig template like node.html.twig. This tutorial explains how to pass props and slots to the component, how to determine the correct namespace and name, and how to choose between Twig’s {% include %} and {% embed %} when rendering an SDC. This technique is most often used by theme developers who override templates and compose a page using single directory components. A common scenario is expressing your design system as components in a theme, then overriding templates to use those components.

In this tutorial, we will:

• Reference a component from a parent Twig template file.
• Pass props and slot values to a component from that template.
• Decide when to use {% include %} or {% embed %} based on the component's slot structure.

By the end of this tutorial, you’ll be able to embed a component into a Twig template and pass values to both its props and slots.

Overriding Single Directory Components (SDCs) allows you to safely customize the functionality and appearance of components provided by contrib modules or themes. Instead of editing the original files, copy a component into your theme, declare that it replaces the original, and then make the necessary adjustments. This approach ensures our changes are upgrade-safe and easy to maintain.

In this tutorial, we will:

• Copy an existing SDC into a theme.
• Use the replaces: key in the component metadata to declare the override.
• Modify the component Twig, CSS, or JavaScript and confirm the changes appear on our site.

By the end of this tutorial, you should be able to override SDCs safely and maintain your customizations in an upgrade-safe manner.