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summary: "Agent-controlled Canvas panel embedded via WKWebView + custom URL scheme"
read_when:
- Implementing the macOS Canvas panel
- Adding agent controls for visual workspace
- Debugging WKWebView canvas loads
title: "Canvas"
---
# Canvas (macOS app)
The macOS app embeds an agent‑controlled **Canvas panel** using `WKWebView`. It
is a lightweight visual workspace for HTML/CSS/JS, A2UI, and small interactive
UI surfaces.
## Where Canvas lives
Canvas state is stored under Application Support:
- `~/Library/Application Support/OpenClaw/canvas/<session>/...`
The Canvas panel serves those files via a **custom URL scheme**:
- `openclaw-canvas://<session>/<path>`
Examples:
- `openclaw-canvas://main/` → `<canvasRoot>/main/index.html`
- `openclaw-canvas://main/assets/app.css` → `<canvasRoot>/main/assets/app.css`
- `openclaw-canvas://main/widgets/todo/` → `<canvasRoot>/main/widgets/todo/index.html`
If no `index.html` exists at the root, the app shows a **built‑in scaffold page**.
## Panel behavior
- Borderless, resizable panel anchored near the menu bar (or mouse cursor).
- Remembers size/position per session.
- Auto‑reloads when local canvas files change.
- Only one Canvas panel is visible at a time (session is switched as needed).
Canvas can be disabled from Settings → **Allow Canvas**. When disabled, canvas
node commands return `CANVAS_DISABLED`.
## Agent API surface
Canvas is exposed via the **Gateway WebSocket**, so the agent can:
- show/hide the panel
- navigate to a path or URL
- evaluate JavaScript
- capture a snapshot image
CLI examples:
```bash
openclaw nodes canvas present --node <id>
openclaw nodes canvas navigate --node <id> --url "/"
openclaw nodes canvas eval --node <id> --js "document.title"
openclaw nodes canvas snapshot --node <id>
```
Notes:
- `canvas.navigate` accepts **local canvas paths**, `http(s)` URLs, and `file://` URLs.
- If you pass `"/"`, the Canvas shows the local scaffold or `index.html`.
## A2UI in Canvas
A2UI is hosted by the Gateway canvas host and rendered inside the Canvas panel.
When the Gateway advertises a Canvas host, the macOS app auto‑navigates to the
A2UI host page on first open.
Default A2UI host URL:
```
http://<gateway-host>:18793/__openclaw__/a2ui/
```
### A2UI commands (v0.8)
Canvas currently accepts **A2UI v0.8** server→client messages:
- `beginRendering`
- `surfaceUpdate`
- `dataModelUpdate`
- `deleteSurface`
`createSurface` (v0.9) is not supported.
CLI example:
```bash
cat > /tmp/a2ui-v0.8.jsonl <<'EOFA2'
{"surfaceUpdate":{"surfaceId":"main","components":[{"id":"root","component":{"Column":{"children":{"explicitList":["title","content"]}}}},{"id":"title","component":{"Text":{"text":{"literalString":"Canvas (A2UI v0.8)"},"usageHint":"h1"}}},{"id":"content","component":{"Text":{"text":{"literalString":"If you can read this, A2UI push works."},"usageHint":"body"}}}]}}
{"beginRendering":{"surfaceId":"main","root":"root"}}
EOFA2
openclaw nodes canvas a2ui push --jsonl /tmp/a2ui-v0.8.jsonl --node <id>
```
Quick smoke:
```bash
openclaw nodes canvas a2ui push --node <id> --text "Hello from A2UI"
```
## Triggering agent runs from Canvas
Canvas can trigger new agent runs via deep links:
- `openclaw://agent?...`
Example (in JS):
```js
window.location.href = "openclaw://agent?message=Review%20this%20design";
```
The app prompts for confirmation unless a valid key is provided.
## Security notes
- Canvas scheme blocks directory traversal; files must live under the session root.
- Local Canvas content uses a custom scheme (no loopback server required).
- External `http(s)` URLs are allowed only when explicitly navigated.
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