canvas-component-metadata by acquia/nebula

File structure

Every component.yml must include these top-level keys:

name: Component Name # Human-readable display name
machineName: component-name # Machine name in kebab-case
status: true # Whether the component is enabled
required: [] # Array of required prop names
props:
  properties:
    # ... prop definitions
slots: [] # Use [] only when there are no slots; otherwise use an object map

Props

Requirements

Every prop definition must include a title for the UI label. The examples array is required for required props and recommended for all others. Only the first example value is used by Drupal Canvas.

If a prop is listed in required, do not add a fallback/default value for that prop in the React component signature. Required Canvas props should be provided by metadata/editor input rather than silent JSX defaults.

props:
  properties:
    heading:
      title: Heading
      type: string
      examples:
        - Enter a heading...

// Correct: required prop has no fallback default
const Hero = ({ heading }) => <h1>{heading}</h1>;

// Wrong: required prop fallback masks missing required data
const Hero = ({ heading = "Default heading" }) => <h1>{heading}</h1>;

Prop IDs must be camelCase versions of their titles.

The prop ID (the key under properties) must be the camelCase conversion of the title value.

Only include user-facing, Canvas-editable props in component.yml. Implementation-only React props must stay in JSX and must not be added to metadata.

Never include className in component.yml. Treat it as a composition prop for developers, not a Canvas editor control.

# Correct
props:
  properties:
    buttonText:           # camelCase of "Button Text"
      title: Button Text
      type: string
    backgroundColor:      # camelCase of "Background Color"
      title: Background Color
      type: string
    isVisible:            # camelCase of "Is Visible"
      title: Is Visible
      type: boolean

# Wrong
props:
  properties:
    btn_text:             # should be "buttonText" for title "Button Text"
      title: Button Text
    bgColor:              # should be "backgroundColor" for title "Background Color"
      title: Background Color

Prop types

Text

Basic text input. Stored as a string value.

type: string
examples:
  - Hello, world!

Formatted text

Rich text content with HTML formatting support, displayed in a block context.

type: string
contentMediaType: text/html
x-formatting-context: block
examples:
  - <p>This is <strong>formatted</strong> text with HTML.</p>

Link

URL or URI reference for links to internal or external resources.

type: string
format: uri-reference
examples:
  - /about/contact

Note: The format can be either uri (accepts only absolute URLs) or uri-reference (accepts both absolute and relative URLs).

IMPORTANT: Use proper path examples for URL props. Do not use # as an example value for uri-reference props—it can cause validation failures during upload. Always use realistic path-like examples:

# Correct
examples:
  - /resources
  - /about/team
  - https://example.com/page

# Wrong
examples:
  - "#"
  - ""

Image

Reference to an image object with metadata like alt text, dimensions, and file URL. Only the file URL is required to exist, all other metadata is always optional.

type: object
$ref: json-schema-definitions://canvas.module/image
examples:
  - src: >-
      https://images.unsplash.com/photo-1484959014842-cd1d967a39cf?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=1770&q=80
    alt: Woman playing the violin
    width: 1770
    height: 1180

Video

Reference to a video object with metadata like dimensions and file URL. Only the file URL is required to exist, all other metadata is always optional.

type: object
$ref: json-schema-definitions://canvas.module/video
examples:
  - src: https://media.istockphoto.com/id/1340051874/video/aerial-top-down-view-of-a-container-cargo-ship.mp4?s=mp4-640x640-is&k=20&c=5qPpYI7TOJiOYzKq9V2myBvUno6Fq2XM3ITPGFE8Cd8=
    poster: https://example.com/600x400.png

Boolean

True or false value.

type: boolean
examples:
  - false

Integer

Whole number value without decimal places.

type: integer
examples:
  - 42

Number

Numeric value that can include decimal places.

type: number
examples:
  - 3.14

List: text

A predefined list of text options that the user can select from.

type: string
enum:
  - option1
  - option2
  - option3
meta:enum:
  option1: Option 1
  option2: Option 2
  option3: Option 3
examples:
  - option1

List: integer

A predefined list of integer options that the user can select from.

type: integer
enum:
  - 1
  - 2
  - 3
meta:enum:
  1: Option 1
  2: Option 2
  3: Option 3
examples:
  - 1

Enums

Enum values must use lowercase, machine-friendly identifiers. Use meta:enum to provide human-readable display labels for the UI.

Note: Enum values cannot contain dots.

# Correct
enum:
  - left_aligned
  - center_aligned
meta:enum:
  left_aligned: Left aligned
  center_aligned: Center aligned
examples:
  - left_aligned

# Wrong
enum:
  - Left aligned
  - Center aligned

The examples value must be the enum value, not the display label.

Enum values must match JSX component variants

When using class-variance-authority (CVA) or similar libraries in the JSX component, the variant keys must exactly match the enum values defined in component.yml.

// component.yml defines: enum: [left_aligned, center_aligned]
// CVA variants must match:
const variants = cva("base-classes", {
  variants: {
    layout: {
      left_aligned: "text-left", // matches enum value
      center_aligned: "text-center", // matches enum value
    },
  },
});

Slots

Slots allow other components to be embedded within a component. In React, each slot is received as a named prop that matches the slot key.

This section is the slot schema source of truth. Other skills should reference these rules instead of redefining slot schema details.

Before creating slots, confirm with the user unless the use case is clearly compositional (for example, rich nested content, or repeatable embedded components). For simple text-like values, prefer a prop.

Important: Do not map Canvas slots to the children prop by default. If the slot key is content, consume it as content in JSX.

Using a slot key named children is technically possible, but it is not recommended because slot naming often flows into user-facing Canvas labels. Prefer explicit slot keys such as content, media, or actions.

slots must be either:

An object map keyed by slot name (content, sidebar, etc.)
[] when the component has no slots

slots:
  content:
    title: Content
  buttons:
    title: Buttons

In the JSX component, slots are destructured as named props and rendered directly:

const Section = ({ width, content }) => {
  return <div className={sectionVariants({ width })}>{content}</div>;
};

// Wrong when the slot key is `content`: this does not consume the named slot.
const Section = ({ children }) => {
  return <div>{children}</div>;
};

Use slots: [] only when the component has no slots:

slots: []

Do not use arrays of slot objects:

# Wrong
slots:
  - name: content
    title: Content