excalidraw

Excalidraw Diagram Generator (MCP Edition)

Create diagrams on a live Excalidraw canvas using MCP tools. The canvas runs in a browser and updates in real time.

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Mental Model

You are placing shapes on a 2D canvas and drawing arrows between them.

(0,0) ────────── x increases ──────────►
  │
  │   ┌──────────┐      ┌──────────┐
  │   │  Box A   │─────►│  Box B   │
  │   └──────────┘      └──────────┘
  │         │
  y         ▼
  increases ┌──────────┐
  │         │  Box C   │
  ▼         └──────────┘

Everything is (x, y, width, height). That's it.

---

The 5 Tools You Actually Need

Tool	What It Does	When to Use
read_diagram_guide	Returns color palette + sizing rules	First call. Read once, use throughout.
batch_create_elements	Create many shapes + arrows at once	Main workhorse. Create your whole diagram in 1-2 calls.
get_canvas_screenshot	Take a photo of the current canvas	After every batch. Verify it looks right.
clear_canvas	Wipe everything	Start fresh before a new diagram.
export_to_image	Save as PNG or SVG	Final step if user wants an image file.

Other useful tools: describe_scene (text description of canvas), create_from_mermaid (quick diagram from Mermaid syntax), export_scene (save as .excalidraw JSON file), set_viewport (zoom/pan to fit), export_to_excalidraw_url (shareable link).

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How Shapes Work

A shape has: type, position (x, y), size (width, height), colors, and label text.

{
  "type": "rectangle",
  "id": "my-box",
  "x": 100,
  "y": 100,
  "width": 180,
  "height": 70,
  "backgroundColor": "#a5d8ff",
  "strokeColor": "#1971c2",
  "roughness": 0,
  "text": "My Service\nPort 8080"
}

Key points:

• text puts a label directly inside the shape (MCP handles the binding for you)
• roughness: 0 = clean lines. roughness: 1 = hand-drawn look.
• Use \n for multi-line labels
• Shapes: rectangle, ellipse, diamond, text (standalone)

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How Arrows Work

Arrows connect shapes by ID. The MCP server auto-routes them to shape edges.

{
  "type": "arrow",
  "x": 0,
  "y": 0,
  "startElementId": "my-box",
  "endElementId": "other-box",
  "strokeColor": "#1971c2",
  "text": "HTTP"
}

Key points:

• startElementId / endElementId = the id of the shape to connect to
• The arrow auto-routes to the nearest edges. You do NOT calculate edge points.
• x, y are still required but can be approximate — binding overrides them
• text adds a label on the arrow
• strokeStyle: "dashed" = async/optional flows. "dotted" = weak dependency.
• startArrowhead / endArrowhead = "arrow", "dot", "triangle", "bar", or null

---

Step-by-Step Workflow

Step 1: Understand What to Draw

Read the codebase. Identify:

• Components (services, databases, APIs, queues, frontends)
• Connections (which components talk to which, and how)
• Layers (group related components into rows or zones)

When a sample diagram is provided (ASCII art, text mockup, screenshot, etc.):

• Preserve ALL text and detail from the sample by default. Do not simplify, summarize, or omit labels, annotations, bullet points, or sublabels present in the sample.
• Extract every node's full text (titles, subtitles, tool names, metrics, details) and reproduce it verbatim in shape labels using \n for multiline.
• Preserve section headers, status annotations (e.g. "Fail = Stop & Notify"), and arrow labels exactly as written.
• Size boxes large enough to fit the full text (increase height/width beyond defaults as needed).
• The sample is the source of truth for content — you may improve layout, colors, and styling, but never drop information.

Step 2: Read the Design Guide

mcp__excalidraw__read_diagram_guide()

This returns the color palette, sizing rules, and layout best practices. Use it.

Step 3: Clear and VERIFY the Canvas

mcp__excalidraw__clear_canvas()
mcp__excalidraw__get_canvas_screenshot()  // MUST verify empty!

Critical: Previous diagrams can leave ghost elements. Always screenshot after clearing to confirm the canvas is truly empty before creating new elements. If elements remain, clear again.

Step 4: Plan Your Layout on Paper

Before calling any create tool, sketch the layout mentally:

Vertical flow (most common):
  Row 1 (y=0):    Zone backgrounds (large dashed rectangles)
  Row 2 (y=60):   Entry points / Users
  Row 3 (y=350):  Middle layer (APIs, services)
  Row 4 (y=650):  Data layer (databases, storage)

  Columns: x = 40, 440, 840  (spaced 400px apart for labeled arrows)
  Box size: 230 x 160 (standard)  |  200 x 120 (for decision diamonds)
  Spacing between rows: ~200px gap after accounting for box height
  Spacing between boxes in a row: 180px gap (for arrow labels)

Step 5: Create Everything in One Batch

Call batch_create_elements with ALL elements at once. This ensures arrow bindings resolve correctly (arrows can reference shape IDs created in the same batch).

Order of elements in the array:

1. Zone backgrounds (large dashed rectangles) — so they render behind everything
2. Shapes (rectangles, ellipses, diamonds) — with id set for arrow references
3. Arrows — using startElementId / endElementId
4. Standalone text labels (titles, annotations)

Step 6: Self-Critique Loop (automatic)

Automatically validate and fix layout before presenting to the user. Do NOT show the diagram until this loop passes or 2 rounds complete.

Skip for diagrams with fewer than 6 elements.

6a. Snapshot for rollback

mcp__excalidraw__snapshot_scene()

If fixes make things worse, restore with mcp__excalidraw__restore_snapshot().

6b. Geometric validation (via query_elements)

mcp__excalidraw__query_elements({ type: "all" })

Check element positions and sizes programmatically:

Check	Detect	Fix
Overlapping shapes	Bounding boxes intersect on both axes	Move one element +200px on x or y
Cramped spacing	Edges <100px apart	Shift apart, recalculate zone boundaries
Zone not wrapping children	Zone bounds don't contain all children with 50px padding	Recalculate: leftmost_child_x - 50 to rightmost_child_x + width + 60
Unconnected shapes	Shape has no arrows referencing its ID (and should)	Add missing arrow or note to user

6c. Visual validation (via screenshot)

mcp__excalidraw__get_canvas_screenshot()

Check for issues requiring visual judgment:

Check	Detect	Fix
Arrow labels clipped	Label text cut off or unreadable	Increase gap between connected shapes to 200px+
Text too small	Labels hard to read	Increase to 16px minimum
Title missing	No diagram title visible	Add text element at y = top_element_y - 60
Diagram off-center	Content clustered in one corner	set_viewport({ scrollToContent: true })

6d. Fix and re-check

Fix issues with update_element or delete_element + create_element, then screenshot again. If the fix made things worse, restore the snapshot.

Constraints:

• Max 2 rounds. After 2, present what you have.
• Only fix layout/visual issues. Do NOT change architectural content.
• Log what you fixed AND what remains unfixed.

Step 7: Present to User

mcp__excalidraw__set_viewport({ scrollToContent: true })
mcp__excalidraw__get_canvas_screenshot()

Show the final screenshot and summarize:

• Components and connections generated
• Auto-fixes applied during self-critique (if any)
• Remaining issues (if any)
• Available next actions (export, refine, drill-down)

Step 8: Export (if requested)

mcp__excalidraw__export_to_image({ format: "png", filePath: "/path/to/output.png" })
mcp__excalidraw__export_scene({ filePath: "/path/to/output.excalidraw" })
mcp__excalidraw__export_to_excalidraw_url()  // shareable link

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Complete Example: 3-Layer Architecture

This shows exactly what to pass to batch_create_elements:

{
  "elements": [
    // --- ZONE BACKGROUNDS (render behind everything) ---
    {
      "type": "rectangle", "id": "zone-frontend",
      "x": 0, "y": 0, "width": 500, "height": 160,
      "backgroundColor": "#e9ecef", "strokeColor": "#868e96",
      "strokeStyle": "dashed", "opacity": 40, "roughness": 0
    },
    {
      "type": "text", "x": 10, "y": 10,
      "text": "Frontend Layer", "fontSize": 14, "strokeColor": "#868e96"
    },
    {
      "type": "rectangle", "id": "zone-backend",
      "x": 0, "y": 200, "width": 500, "height": 160,
      "backgroundColor": "#eebefa", "strokeColor": "#9c36b5",
      "strokeStyle": "dashed", "opacity": 30, "roughness": 0
    },
    {
      "type": "text", "x": 10, "y": 210,
      "text": "Backend Layer", "fontSize": 14, "strokeColor": "#9c36b5"
    },

    // --- SHAPES (give each an id so arrows can reference them) ---
    {
      "type": "rectangle", "id": "react-app",
      "x": 40, "y": 50, "width": 180, "height": 70,
      "backgroundColor": "#a5d8ff", "strokeColor": "#1971c2", "roughness": 0,
      "text": "React App\nFrontend"
    },
    {
      "type": "rectangle", "id": "api-server",
      "x": 40, "y": 250, "width": 180, "height": 70,
      "backgroundColor": "#d0bfff", "strokeColor": "#7048e8", "roughness": 0,
      "text": "API Server\nExpress.js"
    },
    {
      "type": "rectangle", "id": "database",
      "x": 280, "y": 250, "width": 180, "height": 70,
      "backgroundColor": "#b2f2bb", "strokeColor": "#2f9e44", "roughness": 0,
      "text": "PostgreSQL\nDatabase"
    },

    // --- ARROWS (connect shapes by ID) ---
    {
      "type": "arrow", "x": 130, "y": 120,
      "startElementId": "react-app", "endElementId": "api-server",
      "strokeColor": "#1971c2", "text": "REST API"
    },
    {
      "type": "arrow", "x": 220, "y": 285,
      "startElementId": "api-server", "endElementId": "database",
      "strokeColor": "#2f9e44", "text": "SQL"
    },

    // --- TITLE ---
    {
      "type": "text", "x": 100, "y": -40,
      "text": "System Architecture", "fontSize": 24, "strokeColor": "#1e1e1e"
    }
  ]
}

---

Complete Example: Data Flow Diagram (Parameter Threading)

Shows a parameter traced through 5 layers with split/converge paths, decision node, and side annotations:

{
  "elements": [
    // --- TITLE ---
    {"type": "text", "x": 20, "y": 10, "text": "Data Flow: parameter_name Threading", "fontSize": 24, "strokeColor": "#1e1e1e"},
    {"type": "text", "x": 20, "y": 48, "text": "Subtitle describing the trace", "fontSize": 16, "strokeColor": "#868e96"},

    // --- WHY SECTION (top-right, first-principles context) ---
    {"type": "rectangle", "id": "why-bg", "x": 460, "y": 80, "width": 440, "height": 310,
     "backgroundColor": "#e9ecef", "strokeColor": "#868e96", "roughness": 0},
    {"type": "text", "x": 480, "y": 95, "text": "WHY: The Problem", "fontSize": 20, "strokeColor": "#e03131"},
    {"type": "text", "x": 480, "y": 135, "text": "1. What currently happens", "fontSize": 16, "strokeColor": "#1e1e1e"},
    {"type": "text", "x": 480, "y": 195, "text": "2. Why it's expensive/wrong", "fontSize": 16, "strokeColor": "#e03131"},
    {"type": "text", "x": 480, "y": 275, "text": "3. Gap in current design", "fontSize": 16, "strokeColor": "#1e1e1e"},
    {"type": "text", "x": 480, "y": 335, "text": "Solution: what this change does", "fontSize": 16, "strokeColor": "#2f9e44"},

    // --- FLOW BOXES (center column, 150px vertical pitch) ---
    {"type": "rectangle", "id": "l1", "x": 60, "y": 420, "width": 300, "height": 65,
     "backgroundColor": "#a5d8ff", "strokeColor": "#1971c2", "roughness": 0,
     "text": "Entry Point\nfile/path.py"},

    // Split into two paths
    {"type": "rectangle", "id": "l2a", "x": -100, "y": 570, "width": 290, "height": 65,
     "backgroundColor": "#a5d8ff", "strokeColor": "#1971c2", "roughness": 0,
     "text": "Path A\nfile/path_a.py"},
    {"type": "rectangle", "id": "l2b", "x": 230, "y": 570, "width": 290, "height": 65,
     "backgroundColor": "#a5d8ff", "strokeColor": "#1971c2", "roughness": 0,
     "text": "Path B\nfile/path_b.py"},

    // Converge point
    {"type": "rectangle", "id": "l4", "x": 60, "y": 720, "width": 300, "height": 65,
     "backgroundColor": "#eebefa", "strokeColor": "#9c36b5", "roughness": 0,
     "text": "Convergence Point\nfile/path_merge.py"},

    // Decision
    {"type": "diamond", "id": "dec", "x": 110, "y": 870, "width": 200, "height": 120,
     "backgroundColor": "#fff3bf", "strokeColor": "#fab005", "roughness": 0,
     "text": "condition?"},

    // Outcome branches
    {"type": "rectangle", "id": "yes", "x": -100, "y": 1080, "width": 260, "height": 65,
     "backgroundColor": "#ffc9c9", "strokeColor": "#e03131", "roughness": 0,
     "text": "Expensive Operation"},
    {"type": "rectangle", "id": "no", "x": 250, "y": 1080, "width": 220, "height": 65,
     "backgroundColor": "#b2f2bb", "strokeColor": "#2f9e44", "roughness": 0,
     "text": "Skip / Fast Path"},

    // --- ARROWS (bound by ID, auto-routed) ---
    {"type": "arrow", "x": 150, "y": 485, "startElementId": "l1", "endElementId": "l2a",
     "text": "Path A label", "strokeColor": "#1971c2"},
    {"type": "arrow", "x": 280, "y": 485, "startElementId": "l1", "endElementId": "l2b",
     "text": "Path B label", "strokeColor": "#1971c2"},
    {"type": "arrow", "x": 45, "y": 635, "startElementId": "l2a", "endElementId": "l4",
     "text": "data form", "strokeColor": "#9c36b5"},
    {"type": "arrow", "x": 375, "y": 635, "startElementId": "l2b", "endElementId": "l4",
     "text": "data form", "strokeColor": "#1971c2", "strokeStyle": "dashed"},
    {"type": "arrow", "x": 210, "y": 785, "startElementId": "l4", "endElementId": "dec",
     "strokeColor": "#2f9e44"},
    {"type": "arrow", "x": 150, "y": 990, "startElementId": "dec", "endElementId": "yes",
     "text": "True", "strokeColor": "#e03131"},
    {"type": "arrow", "x": 270, "y": 990, "startElementId": "dec", "endElementId": "no",
     "text": "False", "strokeColor": "#2f9e44"},

    // --- LAYER LABELS (left column, gray) ---
    {"type": "text", "x": -100, "y": 420, "text": "Layer 1\nEntry", "fontSize": 14, "strokeColor": "#868e96"},
    {"type": "text", "x": -210, "y": 570, "text": "Layer 2\nBackend", "fontSize": 14, "strokeColor": "#868e96"},

    // --- DATA FORM ANNOTATIONS (right column, orange) ---
    {"type": "text", "x": 570, "y": 440, "text": "Data form: Python bool", "fontSize": 14, "strokeColor": "#e8590c"},
    {"type": "text", "x": 570, "y": 590, "text": "Data form: JSON / arg", "fontSize": 14, "strokeColor": "#e8590c"},
    {"type": "text", "x": 570, "y": 740, "text": "Data form: Dataclass", "fontSize": 14, "strokeColor": "#e8590c"}
  ]
}

---

Color Palette (Quick Reference)

Component Type	Background	Stroke	When to Use
Frontend/UI	#a5d8ff	#1971c2	React, Next.js, web apps
Backend/API	#d0bfff	#7048e8	API servers, processors
Database	#b2f2bb	#2f9e44	PostgreSQL, Redis, MongoDB
Storage	#ffec99	#f08c00	S3, file systems
AI/ML	#e599f7	#9c36b5	ML models, AI services
External API	#ffc9c9	#e03131	Third-party services
Queue/Event	#fff3bf	#fab005	Kafka, RabbitMQ, SQS
Cache	#ffe8cc	#fd7e14	Redis cache, Memcached
Decision/Gate	#ffd8a8	#e8590c	Conditionals, routers
Zone/Group	#e9ecef	#868e96	Logical groupings

Rule: Same-role shapes get same colors. Limit to 3-4 fill colors per diagram.

---

Sizing Rules

Err on the side of too much space. Tight spacing is the #1 mistake — arrows and their labels get hidden when boxes are too close. When in doubt, double the gap you think you need. Diagrams that feel "too spread out" in your head almost always look right on screen.

CRITICAL: Arrow labels need ~120px of clear space between boxes to be visible. If an arrow has a text label (e.g. "auto deploy", "All pass"), the gap between the two connected boxes MUST be at least 150px. Arrows without labels still need 100px minimum.

Property	Value	Why
Box width	200-240px	Fits multiline labels with breathing room
Box height	120-160px	Fits 3-4 line labels comfortably
Horizontal gap (labeled arrows)	150-200px	Arrow labels are ~80-120px wide, need clearance on both sides
Horizontal gap (unlabeled arrows)	100-120px	Just the arrow line + breathing room
Column spacing (labeled)	400px	220px box + 180px gap
Column spacing (unlabeled)	340px	220px box + 120px gap
Row spacing	280-350px	150px box + 150px gap for arrows + annotations
Font size (labels)	16px	Default, readable
Font size (titles)	20-24px	Stands out as header
Font size (zone labels)	14px	Subtle, doesn't compete
Zone opacity	25-40	Background, not foreground
Zone padding	50-60px around children	Zone borders must NOT hug inner boxes
Section header to box gap	40px	Headers need clearance from boxes below

Zone sizing rule: Calculate zone dimensions as: leftmost child x - 50 to rightmost child x + child width + 60 (horizontal), topmost child y - 55 to bottommost child y + child height + 60 (vertical). Always verify the zone fully wraps ALL children with visible padding on every side.

Arrow visibility test: Before finalizing, mentally check every labeled arrow — if the label text is longer than half the gap between boxes, increase the gap. Common offenders: "auto deploy", "rollback on failure", "All pass" — these labels are 80-150px wide and get clipped when gaps are <150px.

---

Layout Patterns

Vertical Flow (default for most diagrams)

Title (y = -40)

[Zone 1: y=0, height=260]
  [Box A: x=40]    [Box B: x=440]    [Box C: x=840]

[Zone 2: y=350, height=260]
  [Box D: x=40]    [Box E: x=440]

[Zone 3: y=700, height=260]
  [Box F: x=240]

Arrows flow top to bottom. Cross-layer arrows use dashed style.

Horizontal Pipeline

[Source] ──► [Transform 1] ──► [Transform 2] ──► [Output]
  x=40        x=440             x=840             x=1240

All at same y. Arrows flow left to right. Use 400px column spacing for labeled arrows, 340px for unlabeled.

Hub and Spoke

         [Consumer A]
              ▲
              │
[Producer] ──► [Event Bus] ──► [Consumer B]
              │
              ▼
         [Consumer C]

Central shape at (300, 300). Spokes at ~200px radius.

Data Flow Diagram (parameter threading, call chains)

Best for: tracing a parameter/request through architectural layers, showing data transformations at each boundary.

 Layer Labels        Main Flow Column          Side Annotations
 (left, gray)        (center, colored)         (right, orange)

  Layer 1      ┌─────────────────────┐         Data form: Python bool
  User API     │  Entry Point        │
               │  file/path.py       │
               └──────┬──────┬───────┘
                      │      │
              ┌───────┘      └────────┐
              ▼                       ▼
  Layer 2  ┌──────────┐    ┌──────────┐        Data form: JSON / bool
  Backend  │ Path A   │    │ Path B   │
           └────┬─────┘    └────┬─────┘
                │               │  (dashed = direct)
                ▼               │
  Layer 3  ┌──────────┐        │               Data form: Dataclass
  HTTP     │ Server   │        │
           └────┬─────┘        │
                └──────┬───────┘  (converge)
                       ▼
  Layer 4  ┌─────────────────────┐             Data form: IPC message
  Manager  │  Manager            │
           └──────┬──────────────┘
                  ▼
  Layer 5  ┌─────────────────────┐             Data form: Conditional
  Executor │  Executor           │
           └──────┬──────────────┘
                  ▼
               ◇ Decision? ◇
              / \
         True/   \False
            ▼     ▼
         [Yes]  [No]

Golden coordinates (validated):

Element	x	y	width	height
Main boxes	60	+150 per row	300	65
Split left	-100	row_y	290	65
Split right	230	row_y	290	65
Decision diamond	110	row_y	200	120
Layer labels	-100 to -50	aligned to box	—	fontSize: 14
Annotations	570	aligned to box	—	fontSize: 14
WHY section	460, y=80	—	440	310

Three-column structure:

• Left column (x < 0): Layer numbers + names in gray (#868e96, fontSize 14)
• Center column (x: 60–360): Flow boxes with ComponentName\nfile/path.py
• Right column (x: 570): Data form annotations in orange (#e8590c, fontSize 14)

Color by layer role:

• Blue (#a5d8ff/#1971c2): User-facing API layers
• Purple (#eebefa/#9c36b5): Internal processing layers
• Green (#b2f2bb/#2f9e44): Execution layer + "skip/success" outcomes
• Yellow (#fff3bf/#fab005): Decision nodes
• Red (#ffc9c9/#e03131): Expensive/dangerous operations
• Gray (#e9ecef/#868e96): Annotations, zones

Split and converge pattern:

• Split: Two arrows from one box, angled down-left and down-right
• Direct skip: Use strokeStyle: "dashed" for paths that skip layers
• Converge: Two arrows from different paths into one box below

"WHY" annotation box (first-principles context): Place a gray-background rectangle (top-right, x: 460) with 3-4 text items explaining the motivation. Use red stroke for the problem, green stroke for the solution.

---

Common Mistakes and Fixes

Mistake	Fix
Ghost elements from previous diagram	Always get_canvas_screenshot() after clear_canvas(). If old elements visible, clear again
Arrows don't connect	Set startElementId/endElementId to valid shape id values
Shapes overlap	Increase spacing. Use 240px column gap, 140px row gap
Labels cut off	Make boxes wider (200px+) or use shorter text
Can't tell layers apart	Add zone background rectangles with dashed stroke + low opacity
Too many colors	Limit to 3-4 fill colors. Same role = same color
Diagram too cluttered	Split into multiple diagrams, or use create_from_mermaid for quick drafts
Arrows cross messily	Rearrange shapes so related ones are adjacent. Vertical flow reduces crossings
Annotations overlap with flow	Use 3-column layout: labels (x<0), flow (x:60-360), annotations (x:570+)
Lost detail from sample diagram	Sample is source of truth for content. Reproduce ALL text verbatim — titles, subtitles, tool lists, metrics, annotations. Size boxes larger if needed
Self-critique finds same issue twice	Fix didn't work — try a different approach (different element, larger gap)
Self-critique runs >2 rounds	Stop and present. List remaining issues for user
Fixed layout but broke arrows	Screenshot after moving shapes to verify bindings. If broken, restore snapshot
Self-critique made things worse	Restore snapshot with restore_snapshot() and present pre-critique version

---

Quick Start Templates

"Draw me a diagram of X"

# 1. Read the code to understand components and connections
# 2. Read the design guide
mcp__excalidraw__read_diagram_guide()
# 3. Clear canvas and verify empty
mcp__excalidraw__clear_canvas()
# 4. Create everything in one batch
mcp__excalidraw__batch_create_elements(elements=[...])
# 5. Self-critique loop runs automatically (snapshot, validate, fix)
# 6. Present to user, then export if requested

"Quick diagram from description"

# For simple diagrams, Mermaid is fastest:
mcp__excalidraw__create_from_mermaid(
  mermaidDiagram="graph TD; A[Frontend] -->|REST| B[API]; B -->|SQL| C[Database]"
)

---

Export Options

Method	Output	Use Case
export_to_image(format="png")	PNG file	Embed in docs, Slack, PRs
export_to_image(format="svg")	SVG file	Scalable, embed in web pages
export_scene(filePath="...")	.excalidraw JSON	Editable in excalidraw.com or VS Code
export_to_excalidraw_url()	Shareable URL	Share with anyone, no file needed