Canvas Skill
Display HTML content on connected Otto 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.rootdirectory - 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/__otto__/canvas/<file>.htmlThis 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 ~/.otto/otto.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>
HTML2. Find your canvas host URL
Check how your gateway is bound:
cat ~/.otto/otto.json | jq '.gateway.bind'Then construct the URL:
- loopback:
http://127.0.0.1:18793/__otto__/canvas/<file>.html - lan/tailnet/auto:
http://<hostname>:18793/__otto__/canvas/<file>.html
Find your Tailscale hostname:
tailscale status --json | jq -r '.Self.DNSName' | sed 's/\.$//'3. Find connected nodes
otto nodes listLook 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/__otto__/canvas/snake.html5. 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 ~/.otto/otto.json | jq '.gateway.bind' - Check what port canvas is on:
lsof -i:18793 - Test URL directly:
curl http://<hostname>:18793/__otto__/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 otto nodes list to find online nodes.
Content not updating
If live reload isn't working:
- Check
liveReload: truein config - Ensure file is in the canvas root directory
- Check for watcher errors in logs
URL Path Structure
The canvas host serves from /__otto__/canvas/ prefix:
http://<host>:18793/__otto__/canvas/index.html → ~/clawd/canvas/index.html
http://<host>:18793/__otto__/canvas/games/snake.html → ~/clawd/canvas/games/snake.htmlThe /__otto__/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
hideit or navigate away - Live reload makes development fast - just save and it updates!
- A2UI JSON push is WIP - use HTML files for now