Excalidraw Diagram Generator

Create Excalidraw-compatible JSON diagrams. Output

.excalidraw.json

files.

JSON Schema

json

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

Coordinate System

Origin: Top-left corner (0, 0)
X-axis: Increases rightward
Y-axis: Increases downward
Unit: Pixels

Grid-Based Layout System

Use a 20px grid for alignment. Standard positions:

GRID_UNIT = 20
COLUMN_WIDTH = 200    # Element + gap
ROW_HEIGHT = 150      # Element + gap

Position formula:
  x = START_X + (column * COLUMN_WIDTH)
  y = START_Y + (row * ROW_HEIGHT)

Recommended START_X = 50, START_Y = 100

Standard Element Sizes

Element	Width	Height	Use Case
Small box	120	60	Labels, simple steps
Standard box	160	80	Process steps
Large box	200	100	Detailed nodes
Wide box	240	80	Long text
Diamond	100	100	Decision points
Circle	80	80	Start/End nodes
Icon circle	90	80	With emoji

Text Centering Formula

CRITICAL: To center text inside a shape:

text_x = shape_x + (shape_width - text_width) / 2
text_y = shape_y + (shape_height - text_height) / 2

Text Size Reference

Font Size	Char Width	Line Height	Use
11	~6px	15px	Labels, annotations
12	~7px	16px	Secondary text
14	~8px	18px	Body text
16	~9px	20px	Primary text
18	~10px	24px	Headings
20	~11px	26px	Titles
28	~16px	35px	Icons/Emoji

Estimate text_width:

char_count * char_width

Estimate text_height:

line_count * line_height

Centering Example

Shape: x=100, y=100, width=160, height=80
Text: "Process" (7 chars), fontSize=16

text_width = 7 * 9 = 63
text_height = 1 * 20 = 20
text_x = 100 + (160 - 63) / 2 = 148.5 ≈ 148
text_y = 100 + (80 - 20) / 2 = 130

Element Types

Common Properties (required for all)

json

{
  "id": "unique-id",
  "type": "rectangle",
  "x": 100,
  "y": 100,
  "width": 160,
  "height": 80,
  "strokeColor": "#1e1e1e",
  "backgroundColor": "transparent",
  "fillStyle": "solid",
  "strokeWidth": 2,
  "roughness": 1,
  "opacity": 100,
  "angle": 0,
  "seed": 100,
  "version": 1,
  "isDeleted": false,
  "boundElements": null,
  "link": null,
  "locked": false
}

Type-Specific Properties

Rectangle: Add

"roundness": {"type": 3}

for rounded corners

Text:

json

{
  "type": "text",
  "text": "Content\nLine 2",
  "fontSize": 16,
  "fontFamily": 1,
  "textAlign": "center",
  "verticalAlign": "middle"
}

fontFamily: 1=Virgil (hand), 2=Helvetica, 3=Cascadia (mono)

Arrow/Line:

json

{
  "type": "arrow",
  "points": [[0, 0], [100, 0]],
  "startArrowhead": null,
  "endArrowhead": "arrow"
}

Points are relative to element's x,y
Arrowheads:
```
null
```
,
```
"arrow"
```
,
```
"bar"
```
,
```
"dot"
```
,
```
"triangle"
```

Arrow Positioning

Horizontal Arrow (Left to Right)

From shape at (x1, y1, w1, h1) to shape at (x2, y2, w2, h2):

arrow_x = x1 + w1           # Right edge of source
arrow_y = y1 + h1/2         # Vertical center
gap = x2 - (x1 + w1)        # Space between shapes
points = [[0, 0], [gap, 0]]

Vertical Arrow (Top to Bottom)

arrow_x = x1 + w1/2         # Horizontal center
arrow_y = y1 + h1           # Bottom edge of source
gap = y2 - (y1 + h1)
points = [[0, 0], [0, gap]]

Diagonal/Curved Arrow

points = [[0, 0], [dx/2, dy], [dx, dy]]  # Curved path

Color Palette

Color	Stroke	Background	Use
Blue	#1971c2	#a5d8ff	Primary, info
Green	#2f9e44	#b2f2bb	Success, start
Orange	#e8590c	#ffc9c9	Warning, action
Red	#e03131	#ffc9c9	Error, end
Purple	#9c36b5	#eebefa	Special, loop
Yellow	#f08c00	#ffec99	Highlight
Teal	#099268	#96f2d7	Secondary
Gray	#868e96	#dee2e6	Neutral, labels
Black	#1e1e1e	-	Text, borders

Z-Order (Element Array Order)

Elements render in array order. First = back, last = front.

Correct order:

Background shapes (containers, frames)
Connection lines/arrows
Foreground shapes (nodes, boxes)
Text labels
Icons/overlays

Layout Patterns

Horizontal Flow (Left to Right)

COL_GAP = 60  # Gap between elements

Element 1: x=50,  y=100, w=160, h=80
Arrow 1:   x=210, y=140, points=[[0,0],[60,0]]
Element 2: x=270, y=100, w=160, h=80
Arrow 2:   x=430, y=140, points=[[0,0],[60,0]]
Element 3: x=490, y=100, w=160, h=80

Vertical Flow (Top to Bottom)

ROW_GAP = 50

Element 1: x=100, y=50,  w=160, h=80
Arrow 1:   x=180, y=130, points=[[0,0],[0,50]]
Element 2: x=100, y=180, w=160, h=80

Decision Branch (Diamond)

Diamond:    x=300, y=200, w=100, h=100
Center:     (350, 250)

Yes path (up-right):
  arrow_x=350, arrow_y=200
  points=[[0,0], [0,-50], [100,-50]]

No path (down-right):
  arrow_x=350, arrow_y=300
  points=[[0,0], [0,50], [100,50]]

Feedback Loop (Return Arrow)

From bottom-right back to left:
  Start: (800, 400)
  points=[
    [0, 0],        # Start
    [0, 80],       # Down
    [-400, 80],    # Left
    [-400, -150]   # Up to target
  ]

Complete Node Example

json

[
  {
    "id": "node1-box",
    "type": "rectangle",
    "x": 100, "y": 100, "width": 160, "height": 80,
    "strokeColor": "#1971c2",
    "backgroundColor": "#a5d8ff",
    "fillStyle": "solid",
    "strokeWidth": 2,
    "roughness": 1,
    "opacity": 100,
    "angle": 0,
    "seed": 100,
    "version": 1,
    "isDeleted": false,
    "boundElements": [{"id": "arrow1", "type": "arrow"}],
    "roundness": {"type": 3},
    "link": null,
    "locked": false
  },
  {
    "id": "node1-text",
    "type": "text",
    "x": 130, "y": 130,
    "width": 100, "height": 20,
    "text": "Process Step",
    "fontSize": 16,
    "fontFamily": 1,
    "textAlign": "center",
    "verticalAlign": "middle",
    "strokeColor": "#1e1e1e",
    "backgroundColor": "transparent",
    "fillStyle": "solid",
    "strokeWidth": 1,
    "roughness": 1,
    "opacity": 100,
    "angle": 0,
    "seed": 101,
    "version": 1,
    "isDeleted": false,
    "boundElements": null,
    "link": null,
    "locked": false
  }
]

Positioning Checklist

Before generating:

☐ Define grid: START_X, START_Y, COLUMN_WIDTH, ROW_HEIGHT
☐ List all elements with row/column positions
☐ Calculate exact x,y using formulas
☐ Calculate text positions using centering formula
☐ Calculate arrow start points and relative endpoints
☐ Order elements correctly for z-order
☐ Assign unique IDs and incrementing seeds

Templates

Basic flowchart:

assets/flowchart-template.excalidraw.json

Processing loop:
```
references/processing-loop-template.md
```
Element specs:
```
references/elements.md
```

Output

Save as
```
.excalidraw.json
```
Copy to
```
/mnt/user-data/outputs/
```
Tell user: "Open at excalidraw.com → Menu → Open"

excalidraw

NPX Install

Tags

SKILL.md Content

Excalidraw Diagram Generator

JSON Schema

Coordinate System

Grid-Based Layout System

Standard Element Sizes

Text Centering Formula

Text Size Reference

Centering Example

Element Types

Common Properties (required for all)

Type-Specific Properties

Arrow Positioning

Horizontal Arrow (Left to Right)

Vertical Arrow (Top to Bottom)

Diagonal/Curved Arrow

Color Palette

Z-Order (Element Array Order)

Layout Patterns

Horizontal Flow (Left to Right)

Vertical Flow (Top to Bottom)

Decision Branch (Diamond)

Feedback Loop (Return Arrow)

Complete Node Example

Positioning Checklist

Templates

Output