Mmcp.market

json-canvas skill

by guanyang·guanyang/open-agent-hub·973 stars·MIT

Create and edit JSON Canvas files (.canvas) with nodes, edges, groups, and connections. Use when working with .canvas files, creating visual canvases, mind maps, flowcharts, or when the user mentions Canvas files in Obsidian.

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Install the json-canvas skill

A skill is a folder. Copy it into your agent's skills folder and the agent loads it when the task matches its description. 

git clone --depth 1 https://github.com/guanyang/open-agent-hub.git /tmp/open-agent-hub
mkdir -p ~/.claude/skills
cp -r /tmp/open-agent-hub/skills/json-canvas ~/.claude/skills/json-canvas
available in every project

In the Claude apps, zip the folder and upload it from the Skills settings. The folder on GitHub

The instructions your agent would load

SKILL.md as published, without the frontmatter. Read it on GitHub

JSON Canvas Skill

File Structure

A canvas file (.canvas) contains two top-level arrays following the JSON Canvas Spec 1.0:

{
  "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

Text Nodes

{
  "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

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

Link Nodes

{
  "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.

{
  "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.

{
  "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 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

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 for full canvas examples including mind maps, project boards, research canvases, and flowcharts.

References

  • JSON Canvas Spec 1.0
  • JSON Canvas GitHub

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