Excalidraw — Hermes-Native Diagram Pipeline

Create Excalidraw diagrams and save them to a diagrams GitHub repo using Hermes tools directly. No MCP dependency — generates standard .excalidraw JSON files.

Prerequisites

Configuration Variables

Set these environment variables or substitute them directly in commands:

Repo Folder Map (suggested)

When to Use

• User says "draw a diagram of..." or "create a visual for..."
• User needs an architecture diagram, flow chart, topology map, or concept sketch
• User wants visuals for a blog post, presentation, video, or documentation

Pipeline Steps

Step 1: Sync the diagrams repo

terminal(command="if [ ! -d {{EXCALIDRAW_REPO_PATH}}/.git ]; then git clone {{EXCALIDRAW_REPO_URL}} {{EXCALIDRAW_REPO_PATH}}; else git -C {{EXCALIDRAW_REPO_PATH}} pull --ff-only origin main; fi", timeout=30)

Step 2: Determine the target folder

Match the diagram purpose to a repo folder from the map above. Default to misc/ if unsure.

Step 3: Design and generate the diagram

Ask the user what the diagram should show. Clarify:

• What elements need to be on the diagram (boxes, labels, connections)
• Which direction the flow goes (top-to-bottom, left-to-right)
• Any colour coding needed

Then write valid Excalidraw JSON. Use the Python generator approach to produce clean, structured diagrams.

Step 4: Create the diagram file

Name the file using kebab-case (e.g. rag-chatbot-architecture.excalidraw).

Save to the correct folder under the repo:

terminal(command="mkdir -p {{EXCALIDRAW_REPO_PATH}}/TARGET_FOLDER && cat > {{EXCALIDRAW_REPO_PATH}}/TARGET_FOLDER/FILENAME.excalidraw << 'JSONEOF'
[GENERATED JSON CONTENT]
JSONEOF", timeout=10)

Or for larger diagrams, write the JSON to a temp file then copy:

terminal(command="python3 /tmp/gen_diagram.py && cp /tmp/diagram_output.json {{EXCALIDRAW_REPO_PATH}}/TARGET_FOLDER/FILENAME.excalidraw", timeout=15)

Step 5: Commit and push

terminal(command="cd {{EXCALIDRAW_REPO_PATH}} && git add . && git commit -m 'diagram: DESCRIPTION' && git push", timeout=30)

Step 6: Report back

Tell the user:

• The diagram file path in the repo: TARGET_FOLDER/FILENAME.excalidraw
• They can view/edit at {{EXCALIDRAW_INSTANCE_URL}} (self-hosted instance or excalidraw.com)
• Or drag-and-drop onto https://excalidraw.com for instant viewing (no account needed)

Excalidraw JSON Structure

A valid .excalidraw file has this structure:

{
  "type": "excalidraw",
  "version": 2,
  "source": "https://excalidraw.com",
  "elements": [
    { /* shapes, text, arrows */ }
  ],
  "appState": {
    "gridSize": null,
    "viewBackgroundColor": "#ffffff"
  }
}

Colour Palette (Standard Excalidraw)

Python Generation Approach

Use the bundled python_helpers.py (in this skill directory) or inline the helper functions to generate diagram JSON programmatically.

The python_helpers.py file provides:

• rect(id, x, y, w, h, label, fill="#a5d8ff") → Returns (rectangle_element, text_element) tuple with boundElements and containerId wired up correctly.
• arrow(id, x, y, dx, dy, start_id, end_id) → Returns an arrow element with startBinding and endBinding set.
• text(id, x, y, w, h, text, container_id=None, **kwargs) → Returns a text element (bound or standalone).
• diagram(title, elements, app_state=None) → Wraps elements into a complete .excalidraw document.

Pitfalls

• Container binding is required. Do NOT use "label": {"text": "..."} on shapes — it is silently ignored by Excalidraw. Use boundElements on the shape + a separate text element with containerId.
• Standalone text (not bound to a shape) needs "containerId": null.
• Camera/pseudo-elements (cameraUpdate) are NOT valid Excalidraw elements — do not include them in the JSON. They are MCP-specific.
• The repo path is ephemeral if stored in a temp directory. Ensure the clone persists or re-clone on each run.
• Git auth: Private repos require SSH key or credential helper. If push fails, the JSON file still exists locally — report the error.
• Large diagrams with many elements can produce JSON files exceeding 100KB. Consider splitting complex diagrams into multiple files. 10–15 elements is a comfortable size for one diagram.
• Fill colours for labels: set "backgroundColor": "transparent" on text elements so they don't obscure the shape's fill colour.