Excalidraw Diagram Generator

You generate .excalidraw files from natural language descriptions. The user can open these files directly in Excalidraw (File → Open) or drag-and-drop onto the canvas.

Workflow

1. Understand the description — identify what the user wants to visualize
2. Auto-select diagram type — choose the best type from the table below
3. Generate the intermediate JSON — write a structured diagram_input.json
4. Run the build script — execute build_excalidraw.py to produce the file
5. Tell the user — report the output file path and how to open it

Diagram Type Selection

When in doubt, prefer flowchart — it handles the widest range of content.

Intermediate JSON Formats

Generate one of the following formats as diagram_input.json in the current working directory.

Flowchart

{
  "type": "flowchart",
  "title": "Short descriptive title",
  "nodes": [
    {"id": "unique_id", "label": "Display Text", "shape": "rectangle"},
    {"id": "decision", "label": "Is it valid?", "shape": "diamond"},
    {"id": "start_end", "label": "Start", "shape": "oval"}
  ],
  "edges": [
    {"from": "node_a", "to": "node_b"},
    {"from": "decision", "to": "node_c", "label": "Yes"},
    {"from": "decision", "to": "node_d", "label": "No"}
  ]
}

Shape choices: rectangle (default), diamond (decisions/conditions), oval (start/end points)

Architecture

{
  "type": "architecture",
  "title": "System Architecture",
  "groups": [
    {
      "id": "frontend",
      "label": "Frontend",
      "nodes": [
        {"id": "web", "label": "Web App"},
        {"id": "mobile", "label": "Mobile App"}
      ]
    },
    {
      "id": "backend",
      "label": "Backend",
      "nodes": [
        {"id": "api", "label": "API Gateway"},
        {"id": "auth", "label": "Auth Service"}
      ]
    }
  ],
  "nodes": [],
  "edges": [
    {"from": "web", "to": "api", "label": "HTTPS"},
    {"from": "mobile", "to": "api", "label": "HTTPS"}
  ]
}

Note: groups is optional. Use nodes at the top level for ungrouped components. You can mix both.

Mind Map

{
  "type": "mindmap",
  "title": "Topic Overview",
  "root": "Central Topic",
  "branches": [
    {
      "label": "Branch 1",
      "children": ["Subtopic A", "Subtopic B", "Subtopic C"]
    },
    {
      "label": "Branch 2",
      "children": ["Subtopic D", "Subtopic E"]
    }
  ]
}

Sequence Diagram

{
  "type": "sequence",
  "title": "Interaction Flow",
  "actors": ["User", "Frontend", "API", "Database"],
  "messages": [
    {"from": "User", "to": "Frontend", "label": "Click Login"},
    {"from": "Frontend", "to": "API", "label": "POST /login"},
    {"from": "API", "to": "Database", "label": "Query user"},
    {"from": "Database", "to": "API", "label": "Return record"},
    {"from": "API", "to": "Frontend", "label": "JWT token"},
    {"from": "Frontend", "to": "User", "label": "Redirect"}
  ]
}

Execution Steps

After writing diagram_input.json, run the build script:

python <skill_dir>/scripts/build_excalidraw.py \
  --input diagram_input.json \
  --output <title>.excalidraw

Where <skill_dir> is the directory containing this SKILL.md file, and <title> is a sanitized version of the diagram title.

Output Message to User

After successful generation, tell the user:

✓ Diagram saved to: <filename>.excalidraw

To open in Excalidraw:
1. Go to https://excalidraw.com
2. Click the menu (☰) → Open → select the file
   — or — drag the file onto the canvas

Tips for Good Diagrams

• Keep labels concise — 1–5 words per node works best
• Limit nodes — 5–15 nodes per diagram for readability; split complex diagrams into multiple files
• Use meaningful IDs — snake_case, no spaces (e.g., api_gateway, check_auth)
• Flowchart edges — always go from a defined node ID to another defined node ID
• Sequence actors — list them in the order they first appear in the conversation

Error Handling

If the script fails:

1. Check that diagram_input.json has valid JSON syntax
2. Ensure all edge from/to values match existing node id values
3. Verify Python 3.6+ is available (python3 --version)