Skills

canvas

Installation
SKILL.md

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)   │
└─────────────────┘     └──────────────────┘     └─────────────┘
  1. Canvas Host Server: Serves static HTML/CSS/JS files from canvasHost.root directory
  2. Node Bridge: Communicates canvas URLs to connected nodes
  3. 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>.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 ~/.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>
HTML

2. 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 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/__otto__/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:

  1. Check server bind: cat ~/.otto/otto.json | jq '.gateway.bind'
  2. Check what port canvas is on: lsof -i :18793
  3. 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:

  1. Check liveReload: true in config
  2. Ensure file is in the canvas root directory
  3. 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.html

The /__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 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
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