Excalidraw

Excalidraw Diagram Skill

Create diagrams by writing standard Excalidraw element JSON and saving as .excalidraw files. These files can be drag-and-dropped onto excalidraw.com for viewing and editing. No accounts, no API keys, no rendering libraries -- just JSON.

Workflow

1. Load this skill (you already did)
2. Write the elements JSON -- an array of Excalidraw element objects
3. Save the file using write_file to create a .excalidraw file
4. Optionally upload for a shareable link using scripts/upload.py via terminal

Saving a Diagram

Wrap your elements array in the standard .excalidraw envelope and save with write_file:

{
  "type": "excalidraw",
  "version": 2,
  "source": "moltis",
  "elements": [ ...your elements array here... ],
  "appState": {
    "viewBackgroundColor": "#ffffff"
  }
}

Save to any path, e.g. ~/diagrams/my_diagram.excalidraw.

Uploading for a Shareable Link

Run the upload script (located in this skill's scripts/ directory) via terminal:

python skills/diagramming/excalidraw/scripts/upload.py ~/diagrams/my_diagram.excalidraw

This uploads to excalidraw.com (no account needed) and prints a shareable URL. Requires the cryptography pip package (pip install cryptography).

Element Format Reference

Required Fields (all elements)

type, id (unique string), x, y, width, height

Defaults (skip these -- they're applied automatically)

• strokeColor: "#1e1e1e"
• backgroundColor: "transparent"
• fillStyle: "solid"
• strokeWidth: 2
• roughness: 1 (hand-drawn look)
• opacity: 100

Canvas background is white.

Element Types

Rectangle:

{ "type": "rectangle", "id": "r1", "x": 100, "y": 100, "width": 200, "height": 100 }

• roundness: { "type": 3 } for rounded corners
• backgroundColor: "#a5d8ff", fillStyle: "solid" for filled

Ellipse:

{ "type": "ellipse", "id": "e1", "x": 100, "y": 100, "width": 150, "height": 150 }

Diamond:

{ "type": "diamond", "id": "d1", "x": 100, "y": 100, "width": 150, "height": 150 }

Labeled shape (container binding) -- create a text element bound to the shape:

WARNING: Do NOT use "label": { "text": "..." } on shapes. This is NOT a valid Excalidraw property and will be silently ignored, producing blank shapes. You MUST use the container binding approach below.

The shape needs boundElements listing the text, and the text needs containerId pointing back:

{ "type": "rectangle", "id": "r1", "x": 100, "y": 100, "width": 200, "height": 80,
  "roundness": { "type": 3 }, "backgroundColor": "#a5d8ff", "fillStyle": "solid",
  "boundElements": [{ "id": "t_r1", "type": "text" }] },
{ "type": "text", "id": "t_r1", "x": 105, "y": 110, "width": 190, "height": 25,
  "text": "Hello", "fontSize": 20, "fontFamily": 1, "strokeColor": "#1e1e1e",
  "textAlign": "center", "verticalAlign": "middle",
  "containerId": "r1", "originalText": "Hello", "autoResize": true }

• Works on rectangle, ellipse, diamond
• Text is auto-centered by Excalidraw when containerId is set
• The text x/y/width/height are approximate -- Excalidraw recalculates them on load
• originalText should match text
• Always include fontFamily: 1 (Virgil/hand-drawn font)

Labeled arrow -- same container binding approach:

{ "type": "arrow", "id": "a1", "x": 300, "y": 150, "width": 200, "height": 0,
  "points": [[0,0],[200,0]], "endArrowhead": "arrow",
  "boundElements": [{ "id": "t_a1", "type": "text" }] },
{ "type": "text", "id": "t_a1", "x": 370, "y": 130, "width": 60, "height": 20,
  "text": "connects", "fontSize": 16, "fontFamily": 1, "strokeColor": "#1e1e1e",
  "textAlign": "center", "verticalAlign": "middle",
  "containerId": "a1", "originalText": "connects", "autoResize": true }

Standalone text (titles and annotations only -- no container):

{ "type": "text", "id": "t1", "x": 150, "y": 138, "text": "Hello", "fontSize": 20,
  "fontFamily": 1, "strokeColor": "#1e1e1e", "originalText": "Hello", "autoResize": true }

• x is the LEFT edge. To center at position cx: x = cx - (text.length * fontSize * 0.5) / 2
• Do NOT rely on textAlign or width for positioning

Arrow:

{ "type": "arrow", "id": "a1", "x": 300, "y": 150, "width": 200, "height": 0,
  "points": [[0,0],[200,0]], "endArrowhead": "arrow" }

• points: [dx, dy] offsets from element x, y
• endArrowhead: null | "arrow" | "bar" | "dot" | "triangle"
• strokeStyle: "solid" (default) | "dashed" | "dotted"

Arrow Bindings (connect arrows to shapes)

{
  "type": "arrow", "id": "a1", "x": 300, "y": 150, "width": 150, "height": 0,
  "points": [[0,0],[150,0]], "endArrowhead": "arrow",
  "startBinding": { "elementId": "r1", "fixedPoint": [1, 0.5] },
  "endBinding": { "elementId": "r2", "fixedPoint": [0, 0.5] }
}

fixedPoint coordinates: top=[0.5,0], bottom=[0.5,1], left=[0,0.5], right=[1,0.5]

Drawing Order (z-order)

• Array order = z-order (first = back, last = front)
• Emit progressively: background zones → shape → its bound text → its arrows → next shape
• BAD: all rectangles, then all texts, then all arrows
• GOOD: bg_zone → shape1 → text_for_shape1 → arrow1 → arrow_label_text → shape2 → text_for_shape2 → ...
• Always place the bound text element immediately after its container shape

Sizing Guidelines

Font sizes:

• Minimum fontSize: 16 for body text, labels, descriptions
• Minimum fontSize: 20 for titles and headings
• Minimum fontSize: 14 for secondary annotations only (sparingly)
• NEVER use fontSize below 14

Element sizes:

• Minimum shape size: 120x60 for labeled rectangles/ellipses
• Leave 20-30px gaps between elements minimum
• Prefer fewer, larger elements over many tiny ones

Color Palette

See references/colors.md for full color tables. Quick reference:

Tips

• Use the color palette consistently across the diagram
• Text contrast is CRITICAL -- never use light gray on white backgrounds. Minimum text color on white: #757575
• Do NOT use emoji in text -- they don't render in Excalidraw's font
• For dark mode diagrams, see references/dark-mode.md
• For larger examples, see references/examples.md