acquia Canonical definition
A Canvas page is a JSON page spec stored in the repository's configured
pagesDir.
Workbench uses these files for local page previews, and the Canvas CLI
push/pull workflow uses them to sync pages between the local project and
Drupal Canvas.
Page specs should fully mirror what authors can build in Drupal Canvas.
Minimum contract (MUST)
Every Canvas page MUST satisfy all checks below:
- The page file exists in the configured pages directory (
pagesDirincanvas.config.json; default./pages) - The page file is a JSON object
- The page includes a non-empty
title - The page includes a
paththat starts with/and is unique within the project - The page includes an
elementsobject with at least one element - Every element in
elementsincludes a discovered componenttype - Any
slotsentries reference element IDs defined in the same file
If any item is missing, the page is incomplete for Canvas usage.
Location and naming
Author the canonical local page specs in the configured pages directory
(pagesDir in canvas.config.json). If pagesDir is not set, Workbench
defaults to the top-level pages/ directory.
- Place each page in
<pages-dir>/<page-name>.json - Keep page files flat in the configured pages directory; nested files are ignored
- Use a stable, descriptive filename that mirrors the page title in a filename-safe way
- Use a human-readable
titleinside the JSON file for the actual page title
Examples:
<pages-dir>/homepage.json<pages-dir>/about-us.json
Treat files in the configured pagesDir as the source of truth for local page
definitions that can be previewed in Workbench and synced with Canvas via the
CLI.
Authored page work is incomplete unless the page is previewable from the
configured pagesDir and ready for validation.
Page file format
Each page file must be a JSON object with:
title: the actual page titlepath: the page's URL path (e.g.,/about). Must start with/and be unique within the project. Other pages link to this page using this value.elements: an object of authored page elements
The page file may also include:
description: a short plain-text summary of the page. Surfaced as page metadata (e.g., for listings or SEO). Leave as an empty string if not set.
Each entry in elements must include:
type: a discovered component type
Each entry may also include:
props: root props for that elementslots: a map of slot names to arrays of element IDs from the same file
Workbench preserves elements insertion order when building the page. Put
top-level sections in the order you want them rendered.
Use the discovered machine-readable component type for each element, such as
card, heading, or js.hero, depending on what Workbench finds in the local
project.
Linking between pages
To link to another page in the project, reference the target page's path.
Example
{
"title": "About",
"path": "/about",
"description": "",
"elements": {
"hero": {
"type": "js.hero",
"props": {
"heading": "About us",
"text": "Learn how our team plans, builds, and ships Canvas experiences.",
"layout": "left_aligned"
}
},
"spacer-lg": {
"type": "js.spacer",
"props": {
"height": "large"
}
},
"body-section": {
"type": "js.section",
"props": {
"width": "normal"
},
"slots": {
"content": ["body-copy"]
}
},
"body-copy": {
"type": "js.text",
"props": {
"content": "<p>Canvas pages should use real component composition rather than custom page wrappers.</p>"
}
}
}
}
Use stable, descriptive element IDs unless you are intentionally preserving IDs from another source such as an exported Canvas page.
Image props in pages
When a component prop is defined as an image in component.yml, page JSON must
pass that prop as a single image object. Match the component prop name exactly
and use the Canvas image shape inside props.
{
"type": "js.card",
"props": {
"image": {
"src": "https://placehold.co/400x300/png",
"alt": "Card placeholder image",
"width": "400",
"height": "300"
},
"heading": "Featured card"
}
}
Supported authored page image sources:
- External
http://orhttps://URLs data:image/...URLs
Do not use local file paths in page JSON. CLI media upload from local files is not supported.
If page media reconciliation or page sync adds resolved image data such as
width, height, or _provenance, preserve that data unless you are
intentionally changing the image source.
Content Entity Reference Props In Pages
When a component prop is defined as a content entity reference in
component.yml, page JSON should provide the selected entity value for that
prop. Do not put dataDependencies.entityFields or field-browser expressions in
the page spec; those belong in the component metadata.
For authored page specs, use the selected entity reference shape with
target_id. If the resolved runtime shape that JSX receives is unclear, run
npx canvas agents-context cer-preview <component> after the component metadata
exists locally to inspect the resolved prop keys and nested values.
target_id is the Drupal entity ID for the selected entity. Get it from a known
Drupal URL such as /node/123, from a content listing/export that includes
entity IDs, or by querying the site's content API when the task requires
choosing a real entity. If the correct entity cannot be determined, ask the user
for the entity ID. Do not use the entity UUID, path alias, title, or resolved
preview object as target_id.
{
"type": "js.article-card",
"props": {
"article": {
"target_id": 123
}
}
}
Format constraints
The page-spec format only supports discovered component elements plus their
props and slots.
That means page specs cannot directly represent:
- Hand-written React wrappers such as
PageLayout - Raw HTML layout elements such as
<div>or<section> className-driven spacing or custom wrapper styling- Inline code duplication of an existing component's markup
If you need a layout primitive, look for an existing component first. If none exists, create it as a component before using it in a page spec.
Validation
Validate every authored page before finishing.
npx canvas validate