SKILL.md•canvas

Canvas Skill

Display HTML content on connected OpenClaw nodes (Mac app, iOS, Android).

Overview

The canvas tool lets you present web content on any connected node's canvas view. Great for:

Displaying games, visualizations, dashboards
Showing generated HTML content
Interactive demos

How It Works

Architecture

┌─────────────────┐     ┌──────────────────┐     ┌─────────────┐
│  Canvas Host    │────▶│   Node Bridge    │────▶│  Node App   │
│  (HTTP Server)  │     │  (TCP Server)    │     │ (Mac/iOS/   │
│  Port 18793     │     │  Port 18790      │     │  Android)   │
└─────────────────┘     └──────────────────┘     └─────────────┘

Canvas Host Server: Serves static HTML/CSS/JS files from canvasHost.root directory
Node Bridge: Communicates canvas URLs to connected nodes
Node Apps: Render the content in a WebView

Tailscale Integration

The canvas host server binds based on gateway.bind setting:

Bind Mode	Server Binds To	Canvas URL Uses
`loopback`	127.0.0.1	localhost (local only)
`lan`	LAN interface	LAN IP address
`tailnet`	Tailscale interface	Tailscale hostname
`auto`	Best available	Tailscale > LAN > loopback

Key insight: The canvasHostHostForBridge is derived from bridgeHost. When bound to Tailscale, nodes receive URLs like:

http://<tailscale-hostname>:18793/__openclaw__/canvas/<file>.html

This is why localhost URLs don't work - the node receives the Tailscale hostname from the bridge!

Actions

Action	Description
`present`	Show canvas with optional target URL
`hide`	Hide the canvas
`navigate`	Navigate to a new URL
`eval`	Execute JavaScript in the canvas
`snapshot`	Capture screenshot of canvas

Configuration

In ~/.openclaw/openclaw.json:

{
  "canvasHost": {
    "enabled": true,
    "port": 18793,
    "root": "/Users/you/clawd/canvas",
    "liveReload": true
  },
  "gateway": {
    "bind": "auto"
  }
}

Live Reload

When liveReload: true (default), the canvas host:

Watches the root directory for changes (via chokidar)
Injects a WebSocket client into HTML files
Automatically reloads connected canvases when files change

Great for development!

Workflow

1. Create HTML content

Place files in the canvas root directory (default ~/clawd/canvas/):

cat > ~/clawd/canvas/my-game.html << 'HTML'
<!DOCTYPE html>
<html>
<head><title>My Game</title></head>
<body>
  <h1>Hello Canvas!</h1>
</body>
</html>
HTML

2. Find your canvas host URL

Check how your gateway is bound:

cat ~/.openclaw/openclaw.json | jq '.gateway.bind'

Then construct the URL:

loopback: http://127.0.0.1:18793/__openclaw__/canvas/<file>.html
lan/tailnet/auto: http://<hostname>:18793/__openclaw__/canvas/<file>.html

Find your Tailscale hostname:

tailscale status --json | jq -r '.Self.DNSName' | sed 's/\.$//'

3. Find connected nodes

openclaw nodes list

Look for Mac/iOS/Android nodes with canvas capability.

4. Present content

canvas action:present node:<node-id> target:<full-url>

Example:

canvas action:present node:mac-63599bc4-b54d-4392-9048-b97abd58343a target:http://peters-mac-studio-1.sheep-coho.ts.net:18793/__openclaw__/canvas/snake.html

5. Navigate, snapshot, or hide

canvas action:navigate node:<node-id> url:<new-url>
canvas action:snapshot node:<node-id>
canvas action:hide node:<node-id>

Debugging

White screen / content not loading

Cause: URL mismatch between server bind and node expectation.

Debug steps:

Check server bind: cat ~/.openclaw/openclaw.json | jq '.gateway.bind'
Check what port canvas is on: lsof -i :18793
Test URL directly: curl http://<hostname>:18793/__openclaw__/canvas/<file>.html

Solution: Use the full hostname matching your bind mode, not localhost.

"node required" error

Always specify node:<node-id> parameter.

"node not connected" error

Node is offline. Use openclaw nodes list to find online nodes.

Content not updating

If live reload isn't working:

Check liveReload: true in config
Ensure file is in the canvas root directory
Check for watcher errors in logs

URL Path Structure

The canvas host serves from /__openclaw__/canvas/ prefix:

http://<host>:18793/__openclaw__/canvas/index.html  → ~/clawd/canvas/index.html
http://<host>:18793/__openclaw__/canvas/games/snake.html → ~/clawd/canvas/games/snake.html

The /__openclaw__/canvas/ prefix is defined by CANVAS_HOST_PATH constant.

Tips

Keep HTML self-contained (inline CSS/JS) for best results
Use the default index.html as a test page (has bridge diagnostics)
The canvas persists until you hide it or navigate away
Live reload makes development fast - just save and it updates!
A2UI JSON push is WIP - use HTML files for now

> canvas