json-canvas

# JSON Canvas Skill

## Mindset

JSON Canvas is a minimal open standard: nodes positioned on an infinite grid, connected by edges. The entire spec fits in two arrays. Design with this simplicity in mind — when a layout feels complex, it is usually a positioning or ID-management problem, not a schema problem.

**When to apply:** Creating or editing `.canvas` files, building visual mind maps or flowcharts in Obsidian, or generating canvas files programmatically.
**When NOT to apply:** The user wants a Markdown note, a database view (use Bases), or a diagram format that outputs to image/PDF — JSON Canvas is a live interactive format, not a rendering target.

## 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"`) |

| Type | Extra Required Field | Notes |
|------|---------------------|-------|
| `text` | `text` (string) | Markdown content; use `\n` for newlines, NEVER `\\n` |
| `file` | `file` (path) | Optional `subpath` for heading/block anchor |
| `link` | `url` (string) | External URL |
| `group` | none | Optional `label`, `background`, `backgroundStyle` |

See [NODE-REFERENCE.md](references/NODE-REFERENCE.md) for full attribute tables and JSON examples for each type.

## 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 cleaner layouts

| Node Type | Suggested Width | Suggested Height |
|-----------|-----------------|------------------|
| Small text | 200-300 | 80-150 |
| Medium text | 300-450 | 150-300 |
| Large text | 400-600 | 300-500 |
| File preview | 300-500 | 200-400 |
| Link preview | 250-400 | 100-200 |

## Validation Checklist

After creating or editing a canvas file, verify:

1. All `id` values are unique across both nodes and edges
2. Every `fromNode` and `toNode` references an existing node ID
3. Required fields are present for each node type (`text` for text nodes, `file` for file nodes, `url` for link nodes)
4. `type` is one of: `text`, `file`, `link`, `group`
5. `fromSide`/`toSide` values are one of: `top`, `right`, `bottom`, `left`
6. `fromEnd`/`toEnd` values are one of: `none`, `arrow`
7. Color presets are `"1"` through `"6"` or valid hex (e.g., `"#FF0000"`)
8. JSON is valid and parseable

If validation fails, check for duplicate IDs, dangling edge references, or malformed JSON strings (especially unescaped newlines in text content).

## Complete Examples

See [references/EXAMPLES.md](references/EXAMPLES.md) for full canvas examples including mind maps, project boards, research canvases, and flowcharts.

## Common Mistakes

**NEVER** embed literal newlines in JSON string values — use `\n`. **NEVER** use `\\n` — it renders as literal backslash-n on screen.
**NEVER** reuse the same `id` across nodes or edges — duplicates silently overwrite each other with no error.
**NEVER** reference a `fromNode`/`toNode` ID that does not exist in `nodes` — the edge renders invisibly.
**NEVER** place child nodes outside the group's coordinate bounds — they appear as free-floating items.
**NEVER** set `fromEnd`/`toEnd` to anything other than `"none"` or `"arrow"` — other values are silently discarded.
**NEVER** supply a bare integer for `color` — the `canvasColor` type requires a quoted string (`"1"`, not `1`).

**WHY:** JSON Canvas validation errors are silent — corrupted files and dangling references produce no error messages, making bad state invisible until the canvas is manually inspected.

See [COMMON-MISTAKES.md](references/COMMON-MISTAKES.md) for full Bad/Good JSON examples.

## References

- [JSON Canvas Spec 1.0](https://jsoncanvas.org/spec/1.0/)
- [JSON Canvas GitHub](https://github.com/obsidianmd/jsoncanvas)