Core

Excalidraw Diagram Creator

Generate .excalidraw JSON files that argue visually, not just display information.

Setup: If the user asks you to set up this skill (renderer, dependencies, etc.), use the installed adapter docs or the project README.

Output Contract

When you create or edit a diagram:

1. Produce a valid .excalidraw JSON file, not a prose-only answer.
2. Use this envelope: type, version, source, elements, appState, and files.
3. If the user names an output path, write there. Otherwise use ./diagram.excalidraw.
4. Prefer the active theme for all color, typography, element, and layout decisions.
5. Render and inspect the PNG when a renderer is available. Fix visible defects before stopping.
6. In the final response, report the .excalidraw path, rendered image path if created, theme used, and any validation caveats.

Do not add nonstandard Excalidraw properties such as label. Labels are text elements. For shape labels, bind a text element to the container with containerId, and keep the text element immediately after its container in elements.

Customization

All colors, typography, and layout rules live in the active theme. Themes are standalone packages: default-sketchy is bundled in core; additional themes ship as @excalidraw-skill-pack/theme-* (npm) or excalidraw-skill-pack-theme-* (PyPI).

The active theme is resolved per call (--theme flag), per project (.excalidraw-skill-pack.json), or globally (~/.excalidraw-skill-pack/config.json). The MCP server's generate_diagram_prompt tool splices the active theme's palette.md and any requested layouts/<template>.md into the agent's system prompt at call time.

To author a new theme: npx @excalidraw-skill-pack/create-theme my-brand. See https://excalidraw-skill-pack.vercel.app/themes/create.

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Core Philosophy

Diagrams ARGUE, not DISPLAY.

A diagram isn't formatted text. It's a visual argument that shows relationships, causality, and flow that words alone can't express. The shape should BE the meaning.

The Isomorphism Test: If you removed all text, would the structure alone communicate the concept? If not, redesign.

The Education Test: Could someone learn something concrete from this diagram, or does it just label boxes? A good diagram teaches—it shows actual formats, real event names, concrete examples.

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Depth Assessment (Do This First)

Before designing, determine what level of detail this diagram needs:

Simple/Conceptual Diagrams

Use abstract shapes when:

• Explaining a mental model or philosophy
• The audience doesn't need technical specifics
• The concept IS the abstraction (e.g., "separation of concerns")

Comprehensive/Technical Diagrams

Use concrete examples when:

• Diagramming a real system, protocol, or architecture
• The diagram will be used to teach or explain (e.g., YouTube video)
• The audience needs to understand what things actually look like
• You're showing how multiple technologies integrate

For technical diagrams, you MUST include evidence artifacts (see below).

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Research Mandate (For Technical Diagrams)

Before drawing anything technical, research the actual specifications.

If you're diagramming a protocol, API, or framework:

1. Look up the actual JSON/data formats
2. Find the real event names, method names, or API endpoints
3. Understand how the pieces actually connect
4. Use real terminology, not generic placeholders

Bad: "Protocol" → "Frontend" Good: "AG-UI streams events (RUN_STARTED, STATE_DELTA, A2UI_UPDATE)" → "CopilotKit renders via createA2UIMessageRenderer()"

Research makes diagrams accurate AND educational.

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Evidence Artifacts

Evidence artifacts are concrete examples that prove your diagram is accurate and help viewers learn. Include them in technical diagrams.

Types of evidence artifacts (choose what's relevant to your diagram):

Artifact Type	When to Use	How to Render
Code snippets	APIs, integrations, implementation details	Dark rectangle + syntax-colored text (see color palette for evidence artifact colors)
Data/JSON examples	Data formats, schemas, payloads	Dark rectangle + colored text (see color palette)
Event/step sequences	Protocols, workflows, lifecycles	Timeline pattern (line + dots + labels)
UI mockups	Showing actual output/results	Nested rectangles mimicking real UI
Real input content	Showing what goes IN to a system	Rectangle with sample content visible
API/method names	Real function calls, endpoints	Use actual names from docs, not placeholders

Example: For a diagram about a streaming protocol, you might show:

• The actual event names from the spec (not just "Event 1", "Event 2")
• A code snippet showing how to connect
• What the streamed data actually looks like

Example: For a diagram about a data transformation pipeline:

• Show sample input data (actual format, not "Input")
• Show sample output data (actual format, not "Output")
• Show intermediate states if relevant

The key principle: show what things actually look like, not just what they're called.

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Multi-Zoom Architecture

Comprehensive diagrams operate at multiple zoom levels simultaneously. Think of it like a map that shows both the country borders AND the street names.

Level 1: Summary Flow

A simplified overview showing the full pipeline or process at a glance. Often placed at the top or bottom of the diagram.

Example: Input → Processing → Output or Client → Server → Database

Level 2: Section Boundaries

Labeled regions that group related components. These create visual "rooms" that help viewers understand what belongs together.

Example: Grouping by responsibility (Backend / Frontend), by phase (Setup / Execution / Cleanup), or by team (User / System / External)

Level 3: Detail Inside Sections

Evidence artifacts, code snippets, and concrete examples within each section. This is where the educational value lives.

Example: Inside a "Backend" section, you might show the actual API response format, not just a box labeled "API Response"

For comprehensive diagrams, aim to include all three levels. The summary gives context, the sections organize, and the details teach.

Bad vs Good

Bad (Displaying)	Good (Arguing)
5 equal boxes with labels	Each concept has a shape that mirrors its behavior
Card grid layout	Visual structure matches conceptual structure
Icons decorating text	Shapes that ARE the meaning
Same container for everything	Distinct visual vocabulary per concept
Everything in a box	Free-floating text with selective containers

Simple vs Comprehensive (Know Which You Need)

Simple Diagram	Comprehensive Diagram
Generic labels: "Input" → "Process" → "Output"	Specific: shows what the input/output actually looks like
Named boxes: "API", "Database", "Client"	Named boxes + examples of actual requests/responses
"Events" or "Messages" label	Timeline with real event/message names from the spec
"UI" or "Dashboard" rectangle	Mockup showing actual UI elements and content
~30 seconds to explain	~2-3 minutes of teaching content
Viewer learns the structure	Viewer learns the structure AND the details

Simple diagrams are fine for abstract concepts, quick overviews, or when the audience already knows the details. Comprehensive diagrams are needed for technical architectures, tutorials, educational content, or when you want the diagram itself to teach.

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Container vs. Free-Floating Text

Not every piece of text needs a shape around it. Default to free-floating text. Add containers only when they serve a purpose.

Use a Container When...	Use Free-Floating Text When...
It's the focal point of a section	It's a label or description
It needs visual grouping with other elements	It's supporting detail or metadata
Arrows need to connect to it	It describes something nearby
The shape itself carries meaning (decision diamond, etc.)	Typography alone creates sufficient hierarchy
It represents a distinct "thing" in the system	It's a section title, subtitle, or annotation

Typography as hierarchy: Use font size, weight, and color to create visual hierarchy without boxes. A 28px title doesn't need a rectangle around it.

The container test: For each boxed element, ask "Would this work as free-floating text?" If yes, remove the container.

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Design Process (Do This BEFORE Generating JSON)

Step 0: Assess Depth Required

Before anything else, determine if this needs to be:

• Simple/Conceptual: Abstract shapes, labels, relationships (mental models, philosophies)
• Comprehensive/Technical: Concrete examples, code snippets, real data (systems, architectures, tutorials)

If comprehensive: Do research first. Look up actual specs, formats, event names, APIs.

Step 1: Understand Deeply

Read the content. For each concept, ask:

• What does this concept DO? (not what IS it)
• What relationships exist between concepts?
• What's the core transformation or flow?
• What would someone need to SEE to understand this? (not just read about)

Step 2: Map Concepts to Patterns

For each concept, find the visual pattern that mirrors its behavior:

If the concept...	Use this pattern
Spawns multiple outputs	Fan-out (radial arrows from center)
Combines inputs into one	Convergence (funnel, arrows merging)
Has hierarchy/nesting	Tree (lines + free-floating text)
Is a sequence of steps	Timeline (line + dots + free-floating labels)
Loops or improves continuously	Spiral/Cycle (arrow returning to start)
Is an abstract state or context	Cloud (overlapping ellipses)
Transforms input to output	Assembly line (before → process → after)
Compares two things	Side-by-side (parallel with contrast)
Separates into phases	Gap/Break (visual separation between sections)

Step 3: Ensure Variety

For multi-concept diagrams: each major concept must use a different visual pattern. No uniform cards or grids.

Step 4: Sketch the Flow

Before JSON, mentally trace how the eye moves through the diagram. There should be a clear visual story.

Step 5: Generate JSON

Only now create the Excalidraw elements. See below for how to handle large diagrams.

Step 6: Render & Validate (MANDATORY)

After generating the JSON, you MUST run the render-view-fix loop until the diagram looks right. This is not optional — see the Render & Validate section below for the full process.

Step 7: Report the Artifact

Return the file path and what changed. Do not paste the full JSON unless the user asked for it.

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Excalidraw Correctness Contract

Every generated element must be complete enough for Excalidraw and the renderer to load without repair:

• Include id, type, x, y, width, height, angle, strokeColor, backgroundColor, fillStyle, strokeWidth, strokeStyle, roughness, opacity, seed, version, versionNonce, isDeleted, groupIds, boundElements, link, and locked where applicable.
• Text elements include text, originalText, fontSize, fontFamily, textAlign, verticalAlign, containerId, and lineHeight.
• Bound shape labels use boundElements on the shape and containerId on the text. The text element follows the shape immediately.
• Arrows use points, startBinding, endBinding, startArrowhead, and endArrowhead. Use focus/gap bindings, not ad hoc endpoint guesses.
• Use descriptive, stable IDs such as ingest_box, eval_loop_arrow, artifact_code_text.
• Use unique numeric seed and versionNonce values. For multi-section diagrams, namespace seeds by section.
• Keep opacity: 100; use color, stroke width, scale, and spacing for hierarchy.
• Use roughness: 0 for polished technical diagrams and roughness: 1 only for intentionally sketchy/whiteboard diagrams.
• Keep text readable at export size. Minimum body text is 16px; prefer 18-24px for labels.

See element-templates.md and json-schema.md for copy-paste structures.

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Comprehensive / large diagram strategy

See references/comprehensive-diagrams.md — consult it when building a large or comprehensive diagram section by section.

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Visual language (patterns, shapes, color, layout, text)

See references/visual-language.md — consult it when choosing patterns, shapes, colors, and layout for a diagram.

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Authoring Format: Skeleton (recommended) vs Full Elements

There are two ways to write a diagram. Default to the skeleton format — it is dramatically less verbose and eliminates a whole class of malformed-JSON defects.

Skeleton format (preferred)

Set "type": "excalidraw-skeleton" and write the minimum per element. The renderer hydrates it via Excalidraw's convertToExcalidrawElements, which auto-generates id, seed, versionNonce, boundElements, containerId, the bound text-label elements, and arrow point geometry.

{
  "type": "excalidraw-skeleton",
  "elements": [
    { "type": "rectangle", "id": "ingest", "x": 100, "y": 100, "width": 160, "height": 80,
      "strokeColor": "#1e1e1e", "backgroundColor": "#ffffff", "roughness": 0,
      "label": { "text": "Ingest" } },
    { "type": "ellipse", "id": "store", "x": 480, "y": 110, "width": 140, "height": 80,
      "label": { "text": "Store" } },
    { "type": "arrow", "x": 270, "y": 140, "width": 200, "height": 0,
      "start": { "id": "ingest" }, "end": { "id": "store" }, "label": { "text": "writes" } }
  ]
}

What you still provide:

• type, x, y, and (for shapes) width/height.
• label: { text } for a bound text label — no separate text element, no containerId wiring.
• All style props you'd normally set (strokeColor, backgroundColor, fillStyle, strokeWidth, strokeStyle, roughness, fontSize, fontFamily, opacity) — pull these from the active theme exactly as before. The skeleton only removes boilerplate, not styling control.

Arrow binding — the one gotcha: a bound arrow still needs approximate geometry. Give it x/y (a point near the source) and width/height (the delta toward the target), then:

• bind to existing elements with "start": { "id": "..." } / "end": { "id": "..." }, or
• auto-create new endpoint shapes with "start": { "type": "rectangle" } / "end": { "type": "ellipse" }. Without coordinates (x:0, y:0), the arrow renders detached at the origin.

Frames (native section boundaries): { "type": "frame", "name": "Backend", "children": ["id1", "id2"] }.

Mermaid fast-path (structured diagrams)

For rigid, structured diagrams — flowcharts, sequence diagrams, class diagrams — don't hand-author elements at all. Write Mermaid and let the renderer convert it:

{
  "type": "mermaid",
  "definition": "flowchart LR\n  A[Client] -->|request| B(API)\n  B --> C{Auth?}\n  C -->|yes| D[(DB)]\n  C -->|no| E[Reject]"
}

The renderer parses it with @excalidraw/mermaid-to-excalidraw, hydrates to full elements, and renders in the active theme's hand-drawn style. hydrate works on Mermaid docs too, producing an editable .excalidraw.

When to use which:

• Mermaid — the structure is the whole point (a flow, a sequence, a class hierarchy) and Mermaid's auto-layout is good enough. Cheapest possible authoring.
• Skeleton / full elements — a visual argument: evidence artifacts, multi-zoom, deliberate composition, free-floating text, anything Mermaid's rigid layout can't express. This is where the methodology earns its keep.

Only flowchart/sequence/class are natively supported; other Mermaid types fall back to an image. If a Mermaid diagram comes out looking like a generic labeled grid, that's the signal to switch to the skeleton format and argue.

Hydrating to an openable file

A skeleton file does not open directly in Excalidraw (it expects fully-qualified elements). The renderer reads skeletons fine, but to produce an editable/shareable .excalidraw:

excalidraw-render hydrate diagram.excalidraw -o diagram.full.excalidraw

Draft as a skeleton → render + iterate (fast, cheap) → hydrate to a full file for the final deliverable.

Full-element format

Hand-write fully-qualified elements (the Excalidraw Correctness Contract above governs this path) only when you need control the skeleton can't express — exact seed reproducibility, custom multi-waypoint arrow points, or hand-tuned geometry. For everything else, skeleton wins.

JSON Structure

Full-element envelope (what hydrate produces and what the full-element path uses):

{
  "type": "excalidraw",
  "version": 2,
  "source": "https://excalidraw.com",
  "elements": [...],
  "appState": {
    "viewBackgroundColor": "#ffffff",
    "gridSize": 20
  },
  "files": {}
}

Element Templates

See references/element-templates.md for copy-paste JSON templates for each element type (text, line, dot, rectangle, arrow). Pull colors from references/color-palette.md based on each element's semantic purpose.

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Render & Validate (MANDATORY)

You cannot judge a diagram from JSON alone. After generating or editing the Excalidraw JSON, you MUST render it to PNG, view the image, and fix what you see — in a loop until it's right. This is a core part of the workflow, not a final check.

How to Render

Use the installed renderer (any of these — whichever the environment provides):

# Node CLI (npm)
npx @excalidraw-skill-pack/render <path-to-file.excalidraw> --theme <theme>

# Python CLI (PyPI) — installs the `excalidraw-render` command
excalidraw-render <path-to-file.excalidraw> --theme <theme>

If you're in an MCP-enabled agent, call the render_diagram tool instead. All paths accept full .excalidraw, excalidraw-skeleton, and mermaid documents and write a PNG next to the file. Then use the Read tool on the PNG to actually view it.

The Loop

After generating the initial JSON, run this cycle:

1. Render & View — Run the render script, then Read the PNG.

2. Audit against your original vision — Before looking for bugs, compare the rendered result to what you designed in Steps 1-4. Ask:

• Does the visual structure match the conceptual structure you planned?
• Does each section use the pattern you intended (fan-out, convergence, timeline, etc.)?
• Does the eye flow through the diagram in the order you designed?
• Is the visual hierarchy correct — hero elements dominant, supporting elements smaller?
• For technical diagrams: are the evidence artifacts (code snippets, data examples) readable and properly placed?

3. Check for visual defects:

• Text clipped by or overflowing its container
• Text or shapes overlapping other elements
• Arrows crossing through elements instead of routing around them
• Arrows landing on the wrong element or pointing into empty space
• Labels floating ambiguously (not clearly anchored to what they describe)
• Uneven spacing between elements that should be evenly spaced
• Sections with too much whitespace next to sections that are too cramped
• Text too small to read at the rendered size
• Overall composition feels lopsided or unbalanced

4. Fix — Edit the JSON to address everything you found. Common fixes:

• Widen containers when text is clipped
• Adjust x/y coordinates to fix spacing and alignment
• Add intermediate waypoints to arrow points arrays to route around elements
• Reposition labels closer to the element they describe
• Resize elements to rebalance visual weight across sections

5. Re-render & re-view — Run the render script again and Read the new PNG.

6. Repeat — Keep cycling until the diagram passes both the vision check (Step 2) and the defect check (Step 3). Typically takes 2-4 iterations. Don't stop after one pass just because there are no critical bugs — if the composition could be better, improve it.

When to Stop

The loop is done when:

• The rendered diagram matches the conceptual design from your planning steps
• No text is clipped, overlapping, or unreadable
• Arrows route cleanly and connect to the right elements
• Spacing is consistent and the composition is balanced
• You'd be comfortable showing it to someone without caveats

First-Time Setup

The renderer drives headless Chromium via Playwright. If a render fails because the browser isn't installed:

# Node renderer
npx playwright install chromium
# Python renderer
excalidraw-render --help   # the package installs Playwright; if missing:
python -m playwright install chromium

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Quality Checklist

Depth & Evidence (Check First for Technical Diagrams)

1. Research done: Did you look up actual specs, formats, event names?
2. Evidence artifacts: Are there code snippets, JSON examples, or real data?
3. Multi-zoom: Does it have summary flow + section boundaries + detail?
4. Concrete over abstract: Real content shown, not just labeled boxes?
5. Educational value: Could someone learn something concrete from this?

Conceptual

6. Isomorphism: Does each visual structure mirror its concept's behavior?
7. Argument: Does the diagram SHOW something text alone couldn't?
8. Variety: Does each major concept use a different visual pattern?
9. No uniform containers: Avoided card grids and equal boxes?

Container Discipline

10. Minimal containers: Could any boxed element work as free-floating text instead?
11. Lines as structure: Are tree/timeline patterns using lines + text rather than boxes?
12. Typography hierarchy: Are font size and color creating visual hierarchy (reducing need for boxes)?

Structural

13. Connections: Every relationship has an arrow or line
14. Flow: Clear visual path for the eye to follow
15. Hierarchy: Important elements are larger/more isolated

Technical

16. Text clean: text contains only readable words
17. Font: fontFamily: 3
18. Roughness: roughness: 0 for clean/modern (unless hand-drawn style requested)
19. Opacity: opacity: 100 for all elements (no transparency)
20. Container ratio: <30% of text elements should be inside containers

Visual Validation (Render Required)

21. Rendered to PNG: Diagram has been rendered and visually inspected
22. No text overflow: All text fits within its container
23. No overlapping elements: Shapes and text don't overlap unintentionally
24. Even spacing: Similar elements have consistent spacing
25. Arrows land correctly: Arrows connect to intended elements without crossing others
26. Readable at export size: Text is legible in the rendered PNG
27. Balanced composition: No large empty voids or overcrowded regions