Excalidraw

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

• Check deps — use Kroki (curl) for SVG; use local CLI for PNG
• Plan — identify diagram type, pick a visual pattern, choose color palette
• Generate — write .excalidraw JSON file (section-by-section for large diagrams)
• Export — run Kroki or CLI command
• 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

| Level | Size | Use for |

|-------|------|---------|

| Title | 28px | Diagram title |

| Header | 24px | Section/group headers |

| Label | 20px | Primary element labels |

| Description | 16px | Secondary text, descriptions |

| Note | 14px | Annotations, fine print |

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):

| Category | Fill | Stroke | Use for |

|----------|------|--------|---------|

| Primary / Input | #dbeafe | #1e40af | Entry points, APIs, user-facing |

| Success / Data | #dcfce7 | #166534 | Data stores, success states |

| Warning / Decision | #fef9c3 | #854d0e | Decision points, conditions |

| Error / Critical | #fee2e2 | #991b1b | Errors, alerts, critical paths |

| External / Storage | #f3e8ff | #6b21a8 | External services, databases, AI/ML |

| Process / Default | #e0f2fe | #0369a1 | Standard process steps |

| Trigger / Start | #fed7aa | #c2410c | Start nodes, triggers, events |

| Neutral / Container | #f1f5f9 | #475569 | Groups, swimlanes, backgrounds |

Text colors:

| Level | Color |

|-------|-------|

| Title | #1e293b |

| Label | #334155 |

| Description | #64748b |

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

Arrow semantics

| Style | Meaning |

|-------|---------|

| Solid (strokeStyle: null) | Primary flow, main path |

| Dashed ("dashed") | Response, async, callback |

| Dotted ("dotted") | Optional, reference, weak dependency |

Excalidraw JSON Structure

File skeleton

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

Element types

| type | use for |

|-----------|----------------------------------|

| rectangle | boxes, components, modules |

| ellipse | start/end nodes, databases |

| diamond | decision points |

| arrow | directed connections |

| line | undirected connections |

| text | standalone labels |

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

| Scenario | Spacing |

|----------|---------|

| Labeled arrow gap (between shapes) | 150–200px |

| Unlabeled arrow gap | 100–120px |

| Column spacing (labeled arrows) | 400px (220px box + 180px gap) |

| Column spacing (unlabeled arrows) | 340px (220px box + 120px gap) |

| Row spacing | 280–350px (150px box + 130–200px gap) |

| Zone/container padding | 50–60px around children |

| Zone/container opacity | 25–40 |

| Minimum gap between any elements | 40px |

Flowchart (LR or TB)

• Ellipse for start/end, diamond for decisions, rectangle for process
• 200px horizontal spacing, 150px vertical spacing
• Decision branches: "Yes" goes forward, "No" goes down
• 3–10 steps (max 15)

Architecture / System Diagram

• Column spacing per table above; use labeled arrow spacing when connections have labels
• Group related services in dashed Neutral containers (opacity: 30, padding: 50px)
• Gateway/entry at left or top, databases at right or bottom
• 3–8 entities (max 12)

Sequence Diagram

• 200px between participants (rectangles at top)
• Vertical lifelines as dashed lines
• Horizontal arrows for messages, 60px vertical spacing
• Solid arrow = request, dashed arrow = response

Mind Map

• Central node: largest (200x100), Trigger color
• Level 1: 150x70, Primary color, radial around center
• Level 2: 120x50, Process color
• Level 3: 90x40, Neutral color
• Use lines (not arrows) for connections
• 4–6 branches (max 8), 2–4 sub-topics per branch

Swimlane

• Large transparent rectangles (Neutral fill, "dashed" stroke, opacity: 30) as lane boundaries
• Lane label as free-standing text at top-left of lane (not bound to rectangle), 28px font
• Elements flow left-to-right within lanes
• Arrows cross lanes for handoffs

Section-by-Section Construction

For diagrams with 10+ elements, do NOT generate the entire JSON at once. Build in sections:

• Plan all sections first — list element IDs, positions, and cross-section bindings
• Write section 1 — create the file with initial elements
• Append section 2 — read the file, add new elements to the elements array
• Repeat — continue until all sections are done
• Final pass — verify all boundElements and startBinding/endBinding references are consistent

Namespace element seeds by section (100xxx, 200xxx, 300xxx) to avoid collisions.

Export

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

# SVG via Kroki API
curl -s -X POST https://kroki.io/excalidraw/svg \
  -H "Content-Type: application/json" \
  --data-binary "@diagram.excalidraw" \
  -o diagram.svg

# Via local Kroki Docker (offline)
curl -s -X POST http://localhost:8000/excalidraw/svg \
  -H "Content-Type: application/json" \
  --data-binary "@diagram.excalidraw" \
  -o diagram.svg

Option B: Local CLI (PNG + SVG)

# PNG at 2x scale (recommended)
excalidraw-brute-export-cli -i diagram.excalidraw -o diagram.png -f png -s 2

# PNG at 1x scale
excalidraw-brute-export-cli -i diagram.excalidraw -o diagram.png -f png -s 1

# SVG
excalidraw-brute-export-cli -i diagram.excalidraw -o diagram.svg -f svg -s 1

Required flags: -f (format: png or svg) and -s (scale: 1, 2, or 3).

Anti-Patterns

Never put text on large background/zone rectangles. Excalidraw centers text in the middle of the shape, overlapping contained elements. Instead, use a free-standing text element positioned at the top of the zone.

Avoid cross-zone arrows. Long diagonal arrows create visual spaghetti. Route arrows within zones or along zone edges. If a cross-zone connection is unavoidable, route it along the perimeter.

Use arrow labels sparingly. Labels placed at the arrow midpoint overlap on short arrows. Keep labels to ≤12 characters and ensure ≥120px clear space between connected shapes. Omit labels when the connection meaning is obvious from context.

Don't use filled backgrounds on containers that hold other elements. Use opacity: 30 (or 25-40 range) for zone/container rectangles so contained elements remain visible.

Always set explicit strokeColor on text elements. Text strokeColor is the rendered text color. If omitted, text may inherit the parent shape's background color and become invisible. Use #1e293b (title), #334155 (label), or #64748b (description) from the text color palette.

Common Mistakes

| Mistake | Fix |

|---------|-----|

| Kroki returns error | Ensure file is valid JSON with "type": "excalidraw" and "elements" array |

| Kroki only outputs SVG | Use local CLI (excalidraw-brute-export-cli) for PNG |

| Export fails with "Missing required flag" | Always pass -f png and -s 2 |

| Export fails with "Executable doesn't exist" | Run npx playwright install firefox |

| macOS: timeout waiting for file chooser | Apply the macOS Meta patch above |

| Arrow points not relative to origin | points always start at [0,0] |

| Missing id on elements | Use descriptive string IDs per element |

| Overlapping elements | Use spacing reference table; minimum 40px gap |

| Arrows not interactive in excalidraw.com | Add boundElements to shapes referencing all bound arrows/text |

| Text not centered in shape | Set containerId on text AND add text to shape's boundElements |

| All text same size | Use font size hierarchy: 28 → 24 → 20 → 16 → 14 |

| Diagram looks monotone | Apply semantic colors from the palette, follow 60-30-10 rule |

| Text invisible / same color as background | Always set strokeColor on text elements to a dark color (#1e293b, #334155, or #64748b) |

| Text overlaps inside zone/container | Don't bind text to zone rectangles; use free-standing text at top |

| Text truncated in shapes | Use width formula: max(160, charCount * 9), double for CJK |

| boundElements: [] causes issues | Use null for empty boundElements, never [] |