Authoring Excalidraw Files

Excalidraw Architecture Diagram Generator

Generate architecture diagrams as .excalidraw files from codebase analysis or user specifications.

Prerequisites

• No prerequisites - generates raw JSON
• For visual inspection: Open .excalidraw files in excalidraw.com or VS Code extension

Quick Start

User asks:

"Generate an architecture diagram for this project"
"Create an excalidraw diagram of the system"
"Visualize this codebase structure"
"Draw the infrastructure architecture"

Claude will:

1. Analyze the codebase (any language/framework)
2. Identify components, services, databases, APIs
3. Map relationships and data flows
4. Generate valid .excalidraw JSON
5. Validate the structure
6. User opens in excalidraw.com or VS Code for visual inspection

Critical Rules

1. NEVER Use Diamond Shapes

Diamond arrow connections are broken in raw Excalidraw JSON. Use styled rectangles instead:

2. Labels Require TWO Elements

The label property does NOT work in raw JSON. Every labeled shape needs:

// 1. Shape with boundElements reference
{
  "id": "my-box",
  "type": "rectangle",
  "boundElements": [{ "type": "text", "id": "my-box-text" }]
}

// 2. Separate text element with containerId
{
  "id": "my-box-text",
  "type": "text",
  "containerId": "my-box",
  "text": "My Label"
}

3. Elbow Arrows Need Three Properties

For 90-degree corners (not curved):

{
  "type": "arrow",
  "roughness": 0,        // Clean lines
  "roundness": null,     // Sharp corners
  "elbowed": true        // 90-degree mode
}

4. Arrow Position at Shape Edge

Arrows must start/end at shape edges, not centers:

5. Arrow width/height = Bounding Box

points = [[0, 0], [-440, 0], [-440, 70]]
width = 440   // max(abs(point[0]))
height = 70   // max(abs(point[1]))

Minimal Working Example

Two boxes connected by an arrow (copy and adapt for any diagram):

{
  "type": "excalidraw",
  "version": 2,
  "source": "claude-code-excalidraw-skill",
  "elements": [
    {
      "id": "box-a",
      "type": "rectangle",
      "x": 100,
      "y": 100,
      "width": 160,
      "height": 80,
      "angle": 0,
      "strokeColor": "#1971c2",
      "backgroundColor": "#a5d8ff",
      "fillStyle": "solid",
      "strokeWidth": 2,
      "strokeStyle": "solid",
      "roughness": 1,
      "opacity": 100,
      "groupIds": [],
      "frameId": null,
      "roundness": { "type": 3 },
      "seed": 1,
      "version": 1,
      "versionNonce": 1,
      "isDeleted": false,
      "boundElements": [{ "type": "text", "id": "box-a-text" }],
      "updated": 1,
      "link": null,
      "locked": false
    },
    {
      "id": "box-a-text",
      "type": "text",
      "x": 105,
      "y": 125,
      "width": 150,
      "height": 30,
      "angle": 0,
      "strokeColor": "#1e1e1e",
      "backgroundColor": "transparent",
      "fillStyle": "solid",
      "strokeWidth": 1,
      "strokeStyle": "solid",
      "roughness": 1,
      "opacity": 100,
      "groupIds": [],
      "frameId": null,
      "roundness": null,
      "seed": 2,
      "version": 1,
      "versionNonce": 2,
      "isDeleted": false,
      "boundElements": null,
      "updated": 1,
      "link": null,
      "locked": false,
      "text": "Frontend",
      "fontSize": 16,
      "fontFamily": 1,
      "textAlign": "center",
      "verticalAlign": "middle",
      "containerId": "box-a",
      "originalText": "Frontend",
      "lineHeight": 1.25
    },
    {
      "id": "box-b",
      "type": "rectangle",
      "x": 100,
      "y": 280,
      "width": 160,
      "height": 80,
      "angle": 0,
      "strokeColor": "#7048e8",
      "backgroundColor": "#d0bfff",
      "fillStyle": "solid",
      "strokeWidth": 2,
      "strokeStyle": "solid",
      "roughness": 1,
      "opacity": 100,
      "groupIds": [],
      "frameId": null,
      "roundness": { "type": 3 },
      "seed": 3,
      "version": 1,
      "versionNonce": 3,
      "isDeleted": false,
      "boundElements": [{ "type": "text", "id": "box-b-text" }],
      "updated": 1,
      "link": null,
      "locked": false
    },
    {
      "id": "box-b-text",
      "type": "text",
      "x": 105,
      "y": 305,
      "width": 150,
      "height": 30,
      "angle": 0,
      "strokeColor": "#1e1e1e",
      "backgroundColor": "transparent",
      "fillStyle": "solid",
      "strokeWidth": 1,
      "strokeStyle": "solid",
      "roughness": 1,
      "opacity": 100,
      "groupIds": [],
      "frameId": null,
      "roundness": null,
      "seed": 4,
      "version": 1,
      "versionNonce": 4,
      "isDeleted": false,
      "boundElements": null,
      "updated": 1,
      "link": null,
      "locked": false,
      "text": "API Server",
      "fontSize": 16,
      "fontFamily": 1,
      "textAlign": "center",
      "verticalAlign": "middle",
      "containerId": "box-b",
      "originalText": "API Server",
      "lineHeight": 1.25
    },
    {
      "id": "arrow-a-b",
      "type": "arrow",
      "x": 180,
      "y": 180,
      "width": 0,
      "height": 100,
      "angle": 0,
      "strokeColor": "#1971c2",
      "backgroundColor": "transparent",
      "fillStyle": "solid",
      "strokeWidth": 2,
      "strokeStyle": "solid",
      "roughness": 0,
      "opacity": 100,
      "groupIds": [],
      "frameId": null,
      "roundness": null,
      "seed": 5,
      "version": 1,
      "versionNonce": 5,
      "isDeleted": false,
      "boundElements": null,
      "updated": 1,
      "link": null,
      "locked": false,
      "points": [[0, 0], [0, 100]],
      "lastCommittedPoint": null,
      "startBinding": null,
      "endBinding": null,
      "startArrowhead": null,
      "endArrowhead": "arrow",
      "elbowed": true
    }
  ],
  "appState": {
    "gridSize": 20,
    "viewBackgroundColor": "#ffffff"
  },
  "files": {}
}

Key structure notes:

• Each labeled shape needs TWO elements (shape + text with containerId)
• Arrow x,y is at source edge: (100 + 160/2, 100 + 80) = (180, 180)
• Arrow height matches the vertical distance: 280 - 180 = 100
• Elbow arrows: roughness: 0, roundness: null, elbowed: true

Workflow

Step 1: Analyze Codebase

Discover components by looking for:

Use tools:

• Glob for **/package.json, **/Dockerfile, **/*.tf
• Grep for app.get, @Controller, CREATE TABLE
• Read for README, config files, entry points

Step 2: Plan Layout

Vertical flow (most common):

Row 1: Users/Entry points (y: 100)
Row 2: Frontend/Gateway (y: 250)
Row 3: Orchestration (y: 400)
Row 4: Services (y: 550)
Row 5: Data layer (y: 700)

Columns: x = 100, 300, 500, 700, 900
Element size: 160-200px x 80-90px

Step 3: Generate Elements

For each component:

1. Create shape with unique id
2. Add boundElements referencing text
3. Create text with containerId
4. Choose color based on type (see references/colors.md)

Step 4: Add Connections

For each relationship:

1. Calculate source edge point
2. Calculate target edge point
3. Determine routing pattern
4. Create arrow with points array
5. Set width/height from bounding box

See references/arrows.md for routing patterns.

Step 5: Validate

Run validation script before finalizing:

uv run scripts/validate_excalidraw.py diagram.excalidraw

Checks performed:

• Valid JSON structure
• boundElements/containerId pairs match
• No duplicate IDs
• No diamond shapes
• Elbow arrows have required properties
• Arrow width/height matches points

Step 6: Visual Inspection and Iterate

Open the .excalidraw file for visual inspection:

• Web: Drag file to excalidraw.com
• VS Code: Install "Excalidraw" extension and open file

Note: Claude cannot see the visual output. The user must review the diagram and report any issues.

If the user reports issues:

1. Identify the problem element from their description
2. Fix the JSON
3. Re-validate
4. Ask user to re-inspect
5. Repeat until correct

Validation Checklist

Before writing file:

• Every shape with label has boundElements + text element
• Text elements have containerId matching shape
• Multi-point arrows have elbowed: true, roundness: null, roughness: 0
• Arrow x,y = source shape edge point
• Arrow final point offset reaches target edge
• Arrow width/height = bounding box of points
• No diamond shapes
• No duplicate IDs
• File is valid JSON

Common Issues

Reference Files

Scripts

Usage:

# Validate
uv run scripts/validate_excalidraw.py diagram.excalidraw

# Validate with verbose arrow checks
uv run scripts/validate_excalidraw.py diagram.excalidraw --verbose

# Output as JSON
uv run scripts/validate_excalidraw.py diagram.excalidraw --json

Output

• Location: docs/architecture/ or user-specified
• Filename: Descriptive, e.g., system-architecture.excalidraw
• Testing: Open in https://excalidraw.com or VS Code extension