Excalidraw Diagrams

Overview

Generate .excalidraw JSON files and export to PNG/SVG.

Two export options:

• Kroki API (curl) — zero install, SVG output only
• excalidraw-brute-export-cli — local Firefox-based, PNG + SVG

Supported formats: PNG (local CLI only), SVG (both options). PDF is NOT supported.

When to Use

Explicit triggers: user says "画图", "diagram", "visualize", "flowchart", "draw", "架构图", "流程图"

Proactive triggers:

• Explaining a system with 3+ interacting components
• Describing a multi-step process or decision tree
• Comparing architectures or approaches side by side

Skip when: a simple list or table suffices, or user is in a quick Q&A flow

Prerequisites

Option A: Kroki API (recommended — zero install, SVG only)

# Just needs curl (pre-installed on macOS/Linux/Windows Git Bash)
curl --version

No additional setup. SVG rendered via https://kroki.io.

Option B: Local CLI (required for PNG)

The CLI uses Firefox (not Chromium). Check and install:

npm install -g excalidraw-brute-export-cli
npx playwright install firefox

macOS patch (one-time, required):

CLI_MAIN=$(npm root -g)/excalidraw-brute-export-cli/src/main.js
sed -i '' 's/keyboard.press("Control+O")/keyboard.press("Meta+O")/' "$CLI_MAIN"
sed -i '' 's/keyboard.press("Control+Shift+E")/keyboard.press("Meta+Shift+E")/' "$CLI_MAIN"

Windows/Linux: No patch needed.

Workflow

1. Check deps — use Kroki (curl) for SVG; use local CLI for PNG
2. Plan — identify diagram type, pick a visual pattern, choose color palette
3. Generate — write .excalidraw JSON file (section-by-section for large diagrams)
4. Export — run Kroki or CLI command
5. Report — tell user the output file path

Design Principles

Default style

• roughness: 0 — clean, modern look for all technical diagrams (use 1 only when user requests hand-drawn/casual style)
• fontFamily: 2 (Helvetica) — professional look; use 1 (Virgil) only for casual/sketch style, 3 (Cascadia) for code snippets
• fillStyle: "solid" — default fill

Font size hierarchy

Color palette

Follow the 60-30-10 rule: 60% whitespace/neutral, 30% primary accent, 10% highlight.

Semantic fill colors (use with strokeColor one shade darker):

Text colors:

Rule: Do not invent new colors. Pick from this palette.

Arrow semantics

Excalidraw JSON Structure

File skeleton

{
  "type": "excalidraw",
  "version": 2,
  "source": "claude-code",
  "elements": [],
  "appState": { "viewBackgroundColor": "#ffffff" }
}

Element types

Element sizing

Calculate element width from label text to prevent truncation:

Latin text:  width = max(160, charCount * 9)
CJK text:   width = max(160, charCount * 18)
Mixed text:  estimate each character individually, sum up

Height: use 60 for single-line labels, add 24 per additional line.

Required properties (all elements)

{
  "id": "auth_service",
  "type": "rectangle",
  "x": 100, "y": 100,
  "width": 160, "height": 60,
  "angle": 0,
  "strokeColor": "#1e40af",
  "backgroundColor": "#dbeafe",
  "fillStyle": "solid",
  "strokeWidth": 2,
  "roughness": 0,
  "opacity": 100,
  "seed": 100001,
  "boundElements": [
    { "id": "arrow_to_db", "type": "arrow" },
    { "id": "label_auth", "type": "text" }
  ]
}

Use descriptive string IDs (e.g., "api_gateway", "arrow_gw_to_auth") instead of random strings.

Give each element a unique seed (integer). Namespace by section: 100xxx, 200xxx, 300xxx.

JSON field rules

• boundElements: use null when empty, never []
• updated: always use 1, never timestamps
• Do NOT include: frameId, index, versionNonce, rawText
• points in arrows: always start at [0, 0]
• seed: must be a positive integer, unique per element

Text inside shapes (contained text)

When text belongs inside a shape, bind them bidirectionally:

{
  "id": "label_auth",
  "type": "text",
  "text": "Auth Service",
  "fontSize": 20,
  "fontFamily": 2,
  "textAlign": "center",
  "verticalAlign": "middle",
  "strokeColor": "#1e293b",
  "containerId": "auth_service"
}

CRITICAL: Text strokeColor is the text color. Always set it explicitly to a dark color from the text color palette. Never omit it — omitting strokeColor on text can cause invisible text that blends with the shape background.

The parent shape must list the text in its boundElements:

"boundElements": [{ "id": "label_auth", "type": "text" }]

Arrow binding (bidirectional)

Arrows must bind to shapes, and shapes must reference bound arrows:

{
  "id": "arrow_gw_to_auth",
  "type": "arrow",
  "points": [[0, 0], [200, 0]],
  "startBinding": { "elementId": "api_gateway", "gap": 5, "focus": 0 },
  "endBinding": { "elementId": "auth_service", "gap": 5, "focus": 0 }
}

Both api_gateway and auth_service must include in their boundElements:

"boundElements": [{ "id": "arrow_gw_to_auth", "type": "arrow" }]

Arrow routing

L-shaped (elbow) arrows — orthogonal routing with 3+ points:

"points": [[0, 0], [100, 0], [100, 150]]

Elbowed arrows — automatic right-angle routing:

{
  "type": "arrow",
  "points": [[0, 0], [0, -50], [200, -50], [200, 0]],
  "elbowed": true
}

Curved arrows — smooth routing with waypoints:

{
  "type": "arrow",
  "points": [[0, 0], [50, -40], [200, 0]],
  "roundness": { "type": 2 }
}

Grouping

Related elements share groupIds. Nested groups list IDs innermost-first:

"groupIds": ["inner_group", "outer_group"]

Diagram Patterns

Choose the right visual pattern for each diagram type.

Spacing Reference

Flowchart (LR or TB)

• Ellipse for start/end, diamo