Critical Thinking Mindset — Apply critical thinking, sequential thinking. Every claim needs traced proof, confidence >80% to act. Anti-hallucination: Never present guess as fact — cite sources for every claim, admit uncertainty freely, self-check output for errors, cross-reference independently, stay skeptical of own confidence — certainty without evidence root of all hallucination.

AI Mistake Prevention — Failure modes to avoid on every task:

• Check downstream references before deleting. Deleting components causes documentation and code staleness cascades. Map all referencing files before removal.
• Verify AI-generated content against actual code. AI hallucinates APIs, class names, and method signatures. Always grep to confirm existence before documenting or referencing.
• Trace full dependency chain after edits. Changing a definition misses downstream variables and consumers derived from it. Always trace the full chain.
• Trace ALL code paths when verifying correctness. Confirming code exists is not confirming it executes. Always trace early exits, error branches, and conditional skips — not just happy path.
• When debugging, ask "whose responsibility?" before fixing. Trace whether bug is in caller (wrong data) or callee (wrong handling). Fix at responsible layer — never patch symptom site.
• Assume existing values are intentional — ask WHY before changing. Before changing any constant, limit, flag, or pattern: read comments, check git blame, examine surrounding code.
• Verify ALL affected outputs, not just the first. Changes touching multiple stacks require verifying EVERY output. One green check is not all green checks.
• Holistic-first debugging — resist nearest-attention trap. When investigating any failure, list EVERY precondition first (config, env vars, DB names, endpoints, DI registrations, data preconditions), then verify each against evidence before forming any code-layer hypothesis.
• Surgical changes — apply the diff test. Bug fix: every changed line must trace directly to the bug. Don't restyle or improve adjacent code. Enhancement task: implement improvements AND announce them explicitly.
• Surface ambiguity before coding — don't pick silently. If request has multiple interpretations, present each with effort estimate and ask. Never assume all-records, file-based, or more complex path.

Excalidraw Diagram Creator

Be skeptical. Apply critical thinking, sequential thinking. Every claim needs traced proof, confidence percentages (Idea should be more than 80%).

Generate

.excalidraw

Output directory: Save generated

.excalidraw

docs/diagrams/

docs/diagrams/cqrs-command-flow.excalidraw

docs/diagrams/cross-service-messaging.excalidraw

Setup: If the user asks you to set up this skill (renderer, dependencies, etc.), see

README.md

Customization

All colors and brand-specific styles live in one file:

references/color-palette.md

To make this skill produce diagrams in your own brand style, edit

color-palette.md

Core Philosophy

Diagrams should 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.

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 ATTENTION include evidence artifacts (see below).

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.

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):

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.

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

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

Simple vs Comprehensive (Know Which You Need)

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.

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.

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.

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:

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 ATTENTION 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.

Large / Comprehensive Diagram Strategy

For comprehensive or technical diagrams, you MUST ATTENTION build the JSON one section at a time. Do NOT attempt to generate the entire file in a single pass. This is a hard constraint — Claude Code has a ~32,000 token output limit per response, and a comprehensive diagram easily exceeds that in one shot. Even if it didn't, generating everything at once leads to worse quality. Section-by-section is better in every way.

The Section-by-Section Workflow

Phase 1: Build each section

1. Create the base file with the JSON wrapper (

   type

   ,

   version

   ,

   appState

   ,

   files

   ) and the first section of elements.
2. Add one section per edit. Each section gets its own dedicated pass — take your time with it. Think carefully about the layout, spacing, and how this section connects to what's already there.
3. Use descriptive string IDs (e.g.,

   "trigger_rect"

   ,

   "arrow_fan_left"

   ) so cross-section references are readable.
4. Namespace seeds by section (e.g., section 1 uses 100xxx, section 2 uses 200xxx) to avoid collisions.
5. Update cross-section bindings as you go. When a new section's element needs to bind to an element from a previous section (e.g., an arrow connecting sections), edit the earlier element's

   boundElements

   array at the same time.

Phase 2: Review the whole

After all sections are in place, read through the complete JSON and check:

• Are cross-section arrows bound correctly on both ends?
• Is the overall spacing balanced, or are some sections cramped while others have too much whitespace?
• Do IDs and bindings all reference elements that actually exist?

Fix any alignment or binding issues before rendering.

Phase 3: Render & validate

Now run the render-view-fix loop from the Render & Validate section. This is where you'll catch visual issues that aren't obvious from JSON — overlaps, clipping, imbalanced composition.

Section Boundaries

Plan your sections around natural visual groupings from the diagram plan. A typical large diagram might split into:

• Section 1: Entry point / trigger
• Section 2: First decision or routing
• Section 3: Main content (hero section — may be the largest single section)
• Section 4-N: Remaining phases, outputs, etc.

Each section should be independently understandable: its elements, internal arrows, and any cross-references to adjacent sections.

What NOT to Do

• Don't generate the entire diagram in one response. You will hit the output token limit and produce truncated, broken JSON. Even if the diagram is small enough to fit, splitting into sections produces better results.
• Don't use a coding agent to generate the JSON. The agent won't have sufficient context about the skill's rules, and the coordination overhead negates any benefit.
• Don't write a Python generator script. The templating and coordinate math seem helpful but introduce a layer of indirection that makes debugging harder. Hand-crafted JSON with descriptive IDs is more maintainable.

Visual Pattern Library

Fan-Out (One-to-Many)

Central element with arrows radiating to multiple targets. Use for: sources, PRDs, root causes, central hubs.

        ○
       ↗
  □ → ○
       ↘
        ○

Convergence (Many-to-One)

Multiple inputs merging through arrows to single output. Use for: aggregation, funnels, synthesis.

  ○ ↘
  ○ → □
  ○ ↗

Tree (Hierarchy)

Parent-child branching with connecting lines and free-floating text (no boxes needed). Use for: file systems, org charts, taxonomies.

  label
  ├── label
  │   ├── label
  │   └── label
  └── label

Use

line

Spiral/Cycle (Continuous Loop)

Elements in sequence with arrow returning to start. Use for: feedback loops, iterative processes, evolution.

  □ → □
  ↑     ↓
  □ ← □

Cloud (Abstract State)

Overlapping ellipses with varied sizes. Use for: context, memory, conversations, mental states.

Assembly Line (Transformation)

Input → Process Box → Output with clear before/after. Use for: transformations, processing, conversion.

  ○○○ → [PROCESS] → □□□
  chaos              order

Side-by-Side (Comparison)

Two parallel structures with visual contrast. Use for: before/after, options, trade-offs.

Gap/Break (Separation)

Visual whitespace or barrier between sections. Use for: phase changes, context resets, boundaries.

Lines as Structure

Use lines (type:

line

• Timelines: Vertical or horizontal line with small dots (10-20px ellipses) at intervals, free-floating labels beside each dot
• Tree structures: Vertical trunk line + horizontal branch lines, with free-floating text labels (no boxes needed)
• Dividers: Thin dashed lines to separate sections
• Flow spines: A central line that elements relate to, rather than connecting boxes

Timeline:           Tree:
  ●─── Label 1        │
  │                   ├── item
  ●─── Label 2        │   ├── sub
  │                   │   └── sub
  ●─── Label 3        └── item

Lines + free-floating text often creates a cleaner result than boxes + contained text.

Shape Meaning

Choose shape based on what it represents—or use no shape at all:

ellipse

ellipse

ellipse

diamond

rectangle

ellipse

Rule: Default to no container. Add shapes only when they carry meaning. Aim for <30% of text elements to be inside containers.

Color as Meaning

Colors encode information, not decoration. Every color choice should come from

references/color-palette.md

Key principles:

• Each semantic purpose (start, end, decision, AI, error, etc.) has a specific fill/stroke pair
• Free-floating text uses color for hierarchy (titles, subtitles, details — each at a different level)
• Evidence artifacts (code snippets, JSON examples) use their own dark background + colored text scheme
• Always pair a darker stroke with a lighter fill for contrast

Do not invent new colors. If a concept doesn't fit an existing semantic category, use Primary/Neutral or Secondary.

Modern Aesthetics

For clean, professional diagrams:

Roughness

• roughness: 0

  — Clean, crisp edges. Use for modern/technical diagrams.

• roughness: 1

  — Hand-drawn, organic feel. Use for brainstorming/informal diagrams.

Default to 0 for most professional use cases.

Stroke Width

• strokeWidth: 1

  — Thin, elegant. Good for lines, dividers, subtle connections.

• strokeWidth: 2

  — Standard. Good for shapes and primary arrows.

• strokeWidth: 3

  — Bold. Use sparingly for emphasis (main flow line, key connections).

Opacity

Always use

opacity: 100

Small Markers Instead of Shapes

Instead of full shapes, use small dots (10-20px ellipses) as:

• Timeline markers
• Bullet points
• Connection nodes
• Visual anchors for free-floating text

Layout Principles

Hierarchy Through Scale

• Hero: 300×150 - visual anchor, most important
• Primary: 180×90
• Secondary: 120×60
• Small: 60×40

Whitespace = Importance

The most important element has the most empty space around it (200px+).

Flow Direction

Guide the eye: typically left→right or top→bottom for sequences, radial for hub-and-spoke.

Connections Required

Position alone doesn't show relationships. If A relates to B, there must be an arrow.

Arrow Routing (Preventing Overlap)

Straight arrows are the default, but they cause overlaps in dense diagrams. When arrows cross through other elements, use curved or elbowed routing to clear obstacles. This is especially critical in ERDs, architecture diagrams, and any layout with many connections.

Strategy Selection

1. Straight — Only for direct neighbors with a clear, unobstructed path between them. Use 2 points:

   [[0,0], [dx, dy]]

   .

2. Curved (primary overlap fix) — Use when a straight arrow would cross through other elements. Add

   "roundness": {"type": 2}

   and a 3-point arc:

   [[0,0], [midX, -arcHeight], [endX, endY]]

   . The midpoint's Y offset creates a smooth parabola that clears obstacles. Use 15-30px offset for short arrows, 30-50px for long ones. Negative Y = arc above, positive Y = arc below.

3. Elbowed — Use when curved isn't enough (same-row entities with many obstacles between). Set

   "elbowed": true

   with a 4-point right-angle path:

   [[0,0], [0, -offset], [targetX, -offset], [targetX, 0]]

   . Add

   "fixedSegments"

   to pin the horizontal segment.

Binding Modes

Use the modern binding format with

mode

fixedPoint

focus

gap

• "orbit"

  — Arrow attaches to shape's outer edge. Best for most connections.

  fixedPoint: [xRatio, yRatio]

  where

  [0,0.5]

  = left,

  [1,0.5]

  = right,

  [0.5,0]

  = top,

  [0.5,1]

  = bottom.

• "inside"

  — Arrow starts/ends from inside the shape. Use for vertical drops within a column.

See

references/element-templates.md

When to Audit Arrows

During the render-view-fix loop, specifically check:

• Do any arrows cross through shapes they shouldn't?
• Are parallel arrows distinguishable (not overlapping each other)?
• For fan-out patterns (one entity with 5+ outgoing arrows), consider reducing to essential relationships or using varied arc heights to separate paths.

Text Rules

CRITICAL: The JSON

text

{
    "id": "myElement1",
    "text": "Start",
    "originalText": "Start"
}

Settings:

fontSize: 16

fontFamily: 3

textAlign: "center"

verticalAlign: "middle"

JSON Structure

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

Element Templates

See

references/element-templates.md

references/color-palette.md

Render & Validate (MANDATORY)

You cannot judge a diagram from JSON alone. After generating or editing the Excalidraw JSON, you MUST ATTENTION 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

cd .claude/skills/excalidraw-diagram/references && uv run python render_excalidraw.py <path-to-file.excalidraw>

This outputs a PNG next to the

.excalidraw

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
• Convert overlapping straight arrows to curved (

  roundness: {"type": 2}

  + 3-point arc) or elbowed (

  elbowed: true

  + 4-point path) — see Arrow Routing section
• 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

If the render script hasn't been set up yet:

cd .claude/skills/excalidraw-diagram/references
uv sync
uv run playwright install chromium

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
16. Arrow routing: No arrows crossing through shapes — use curved/elbowed routing where needed

Technical

17. Text clean:

    text

    contains only readable words
18. Font:

    fontFamily: 3

19. Roughness:

    roughness: 0

    for clean/modern (unless hand-drawn style requested)
20. Opacity:

    opacity: 100

    for all elements (no transparency)
21. Container ratio: <30% of text elements should be inside containers

Visual Validation (Render Required)

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

Closing Reminders

• IMPORTANT MUST ATTENTION break work into small todo tasks using

  TaskCreate

  BEFORE starting
• IMPORTANT MUST ATTENTION search codebase for 3+ similar patterns before creating new code
• IMPORTANT MUST ATTENTION cite

  file:line

  evidence for every claim (confidence >80% to act)
• IMPORTANT MUST ATTENTION add a final review todo task to verify work quality <!-- SYNC:critical-thinking-mindset:reminder -->
• MUST ATTENTION apply critical thinking — every claim needs traced proof, confidence >80% to act. Anti-hallucination: never present guess as fact. <!-- /SYNC:critical-thinking-mindset:reminder --> <!-- SYNC:ai-mistake-prevention:reminder -->
• MUST ATTENTION apply AI mistake prevention — holistic-first debugging, fix at responsible layer, surface ambiguity before coding, re-read files after compaction. <!-- /SYNC:ai-mistake-prevention:reminder -->