json-canvas

# JSON Canvas Skill

## File Structure

A canvas file (`.canvas`) contains two top-level arrays following the [JSON Canvas Spec 1.0](https://jsoncanvas.org/spec/1.0/):

```json
{
  "nodes": [],
  "edges": []
}
```

- `nodes` (optional): Array of node objects
- `edges` (optional): Array of edge objects connecting nodes

## Common Workflows

### 1. Create a New Canvas

1. Create a `.canvas` file with the base structure `{"nodes": [], "edges": []}`
2. Generate unique 16-character hex IDs for each node (e.g., `"6f0ad84f44ce9c17"`)
3. Add nodes with required fields: `id`, `type`, `x`, `y`, `width`, `height`
4. Add edges referencing valid node IDs via `fromNode` and `toNode`
5. **Validate**: Parse the JSON to confirm it is valid. Verify all `fromNode`/`toNode` values exist in the nodes array

### 2. Add a Node to an Existing Canvas

1. Read and parse the existing `.canvas` file
2. Generate a unique ID that does not collide with existing node or edge IDs
3. Choose position (`x`, `y`) that avoids overlapping existing nodes (leave 50-100px spacing)
4. Append the new node object to the `nodes` array
5. Optionally add edges connecting the new node to existing nodes
6. **Validate**: Confirm all IDs are unique and all edge references resolve to existing nodes

### 3. Connect Two Nodes

1. Identify the source and target node IDs
2. Generate a unique edge ID
3. Set `fromNode` and `toNode` to the source and target IDs
4. Optionally set `fromSide`/`toSide` (top, right, bottom, left) for anchor points
5. Optionally set `label` for descriptive text on the edge
6. Append the edge to the `edges` array
7. **Validate**: Confirm both `fromNode` and `toNode` reference existing node IDs

### 4. Edit an Existing Canvas

1. Read and parse the `.canvas` file as JSON
2. Locate the target node or edge by `id`
3. Modify the desired attributes (text, position, color, etc.)
4. Write the updated JSON back to the file
5. **Validate**: Re-check all ID uniqueness and edge reference integrity after editing

## Nodes

Nodes are objects placed on the canvas. Array order determines z-index: first node = bottom layer, last node = top layer.

### Generic Node Attributes

| Attribute | Required | Type | Description |
|-----------|----------|------|-------------|
| `id` | Yes | string | Unique 16-char hex identifier |
| `type` | Yes | string | `text`, `file`, `link`, or `group` |
| `x` | Yes | integer | X position in pixels |
| `y` | Yes | integer | Y position in pixels |
| `width` | Yes | integer | Width in pixels |
| `height` | Yes | integer | Height in pixels |
| `color` | No | canvasColor | Preset `"1"`-`"6"` or hex (e.g., `"#FF0000"`) |

### Text Nodes

| Attribute | Required | Type | Description |
|-----------|----------|------|-------------|
| `text` | Yes | string | Plain text with Markdown syntax |

```json
{
  "id": "6f0ad84f44ce9c17",
  "type": "text",
  "x": 0,
  "y": 0,
  "width": 400,
  "height": 200,
  "text": "# Hello World\n\nThis is **Markdown** content."
}
```

**Newline pitfall**: Use `\n` for line breaks in JSON strings. Do **not** use the literal `\\n` -- Obsidian renders that as the characters `\` and `n`.

### File Nodes

| Attribute | Required | Type | Description |
|-----------|----------|------|-------------|
| `file` | Yes | string | Path to file within the system |
| `subpath` | No | string | Link to heading or block (starts with `#`) |

```json
{
  "id": "a1b2c3d4e5f67890",
  "type": "file",
  "x": 500,
  "y": 0,
  "width": 400,
  "height": 300,
  "file": "Attachments/diagram.png"
}
```

### Link Nodes

| Attribute | Required | Type | Description |
|-----------|----------|------|-------------|
| `url` | Yes | string | External URL |

```json
{
  "id": "c3d4e5f678901234",
  "type": "link",
  "x": 1000,
  "y": 0,
  "width": 400,
  "height": 200,
  "url": "https://obsidian.md"
}
```

### Group Nodes

Groups are visual containers for organizing other nodes. Position child nodes inside the group's bounds.

| Attribute | Required | Type | Description |
|-----------|----------|------|-------------|
| `label` | No | string | Text label for the group |
| `background` | No | string | Path to background image |
| `backgroundStyle` | No | string | `cover`, `ratio`, or `repeat` |

```json
{
  "id": "d4e5f6789012345a",
  "type": "group",
  "x": -50,
  "y": -50,
  "width": 1000,
  "height": 600,
  "label": "Project Overview",
  "color": "4"
}
```

## Edges

Edges connect nodes via `fromNode` and `toNode` IDs.

| Attribute | Required | Type | Default | Description |
|-----------|----------|------|---------|-------------|
| `id` | Yes | string | - | Unique identifier |
| `fromNode` | Yes | string | - | Source node ID |
| `fromSide` | No | string | - | `top`, `right`, `bottom`, or `left` |
| `fromEnd` | No | string | `none` | `none` or `arrow` |
| `toNode` | Yes | string | - | Target node ID |
| `toSide` | No | string | - | `top`, `right`, `bottom`, or `left` |
| `toEnd` | No | string | `arrow` | `none` or `arrow` |
| `color` | No | canvasColor | - | Line color |
| `label` | No | string | - | Text label |

```json
{
  "id": "0123456789abcdef",
  "fromNode": "6f0ad84f44ce9c17",
  "fromSide": "right",
  "toNode": "a1b2c3d4e5f67890",
  "toSide": "left",
  "toEnd": "arrow",
  "label": "leads to"
}
```

## Colors

The `canvasColor` type accepts either a hex string or a preset number:

| Preset | Color |
|--------|-------|
| `"1"` | Red |
| `"2"` | Orange |
| `"3"` | Yellow |
| `"4"` | Green |
| `"5"` | Cyan |
| `"6"` | Purple |

Preset color values are intentionally undefined -- applications use their own brand colors.

## ID Generation

Generate 16-character lowercase hexadecimal strings (64-bit random value):

```
"6f0ad84f44ce9c17"
"a3b2c1d0e9f8a7b6"
```

## Layout Guidelines

- Coordinates can be negative (canvas extends infinitely)
- `x` increases right, `y` increases down; position is the top-left corner
- Space nodes 50-100px apart; leave 20-50px padding inside groups
- Align to grid (multiples of 10 or 20) for cleane