# Canvas Skill
Display HTML content on connected Clawdbot 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://:18793/__clawdbot__/canvas/.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 `~/.clawdbot/clawdbot.json`:
```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/`):
```bash
cat > ~/clawd/canvas/my-game.html << 'HTML'
My Game
Hello Canvas!
HTML
```
### 2. Find your canvas host URL
Check how your gateway is bound:
```bash
cat ~/.clawdbot/clawdbot.json | jq '.gateway.bind'
```
Then construct the URL:
- **loopback**: `http://127.0.0.1:18793/__clawdbot__/canvas/.html`
- **lan/tailnet/auto**: `http://:18793/__clawdbot__/canvas/.html`
Find your Tailscale hostname:
```bash
tailscale status --json | jq -r '.Self.DNSName' | sed 's/\.$//'
```
### 3. Find connected nodes
```bash
clawdbot nodes list
```
Look for Mac/iOS/Android nodes with canvas capability.
### 4. Present content
```
canvas action:present node: target:
```
**Example:**
```
canvas action:present node:mac-63599bc4-b54d-4392-9048-b97abd58343a target:http://peters-mac-studio-1.sheep-coho.ts.net:18793/__clawdbot__/canvas/snake.html
```
### 5. Navigate, snapshot, or hide
```
canvas action:navigate node: url:
canvas action:snapshot node:
canvas action:hide node:
```
## Debugging
### White screen / content not loading
**Cause:** URL mismatch between server bind and node expectation.
**Debug steps:**
1. Check server bind: `cat ~/.clawdbot/clawdbot.json | jq '.gateway.bind'`
2. Check what port canvas is on: `lsof -i :18793`
3. Test URL directly: `curl http://:18793/__clawdbot__/canvas/.html`
**Solution:** Use the full hostname matching your bind mode, not localhost.
### "node required" error
Always specify `node:` parameter.
### "node not connected" error
Node is offline. Use `clawdbot 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 `/__clawdbot__/canvas/` prefix:
```
http://:18793/__clawdbot__/canvas/index.html → ~/clawd/canvas/index.html
http://:18793/__clawdbot__/canvas/games/snake.html → ~/clawd/canvas/games/snake.html
```
The `/__clawdbot__/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