Markdown Mermaid

Markdown & Mermaid

Clear documentation through visual excellence

A skill for markdown authoring, Mermaid diagramming, multi-tool visualization, VS Code integration, and cross-platform rendering consistency.

Staleness Watch: See EXTERNAL-API-REGISTRY.md for source URLs and recheck cadence

When to Use

• Creating technical documentation with diagrams
• Choosing the right diagramming tool for your audience
• Troubleshooting Mermaid rendering issues
• Styling markdown previews in VS Code
• Converting unicode escapes to proper emojis
• Enterprise documentation with visual standards
• Interactive diagrams in VS Code chat (1.109+)

⚠️ MANDATORY: Start Every Diagram With This Template

Do NOT write Mermaid code without this template. Copy-paste first, then customize:

%%{init: {'theme': 'base', 'themeVariables': {'lineColor': '#57606a', 'primaryColor': '#ddf4ff', 'primaryBorderColor': '#0969da', 'primaryTextColor': '#1f2328', 'edgeLabelBackground': '#ffffff'}}}%%
flowchart LR
    A[Input]:::blue --> B[Process]:::purple --> C[Output]:::green

    classDef blue fill:#ddf4ff,color:#0550ae,stroke:#80ccff
    classDef green fill:#d3f5db,color:#1a7f37,stroke:#6fdd8b
    classDef purple fill:#d8b9ff,color:#6639ba,stroke:#bf8aff
    classDef gold fill:#fff8c5,color:#9a6700,stroke:#d4a72c
    classDef red fill:#ffebe9,color:#cf222e,stroke:#f5a3a3
    classDef neutral fill:#eaeef2,color:#24292f,stroke:#d0d7de

    linkStyle default stroke:#57606a,stroke-width:1.5px

Three required components:

1. Init directive (line 1) — Sets theme, colors, white edge label background
2. classDef — Semantic colors for all node types
3. linkStyle default — Gray arrows at 1.5px width

Mandatory Workflow: ATACCU

Every Mermaid diagram MUST follow this 6-step protocol. No exceptions — this prevents forgotten palettes, broken layouts, and inconsistent styling.

Pre-Flight Checklist (Steps A-T-A)

Before writing any Mermaid code, answer these:

□ Diagram type selected (flowchart/sequence/gantt/quadrant/etc.)
□ Layout direction chosen (LR preferred for flow, TD for hierarchy)
□ Subgraph strategy decided (Medallion vs Lineage vs Pipeline)
□ Color assignments mapped (what color = what meaning)
□ Multi-line node labels use <br/> NOT \n

Quality Gate (Steps C-C-U)

After creating the diagram, verify ALL of these:

□ Init directive is FIRST line inside mermaid block
□ edgeLabelBackground is '#ffffff' (white background for edge labels)
□ ALL nodes have style/classDef (no unstyled nodes)
□ Colors are GitHub Pastel v2 (NOT saturated: no #51cf66, #339af0, #fab005)
□ linkStyle default stroke:#57606a,stroke-width:1.5px (flowcharts)
□ Node labels use <br/> for line breaks, NOT \n
□ Diagram rendered and visually inspected
□ No dimension > 3x the other (use subgroups to balance)
□ Figure label added below diagram block
□ Written to target file (not just shown in chat)

Common Violations This Prevents

VS Code 1.109+ Native Chat Rendering

VS Code 1.109 introduces native Mermaid rendering in chat via the renderMermaidDiagram tool.

When to Use Native Rendering

When creating diagrams in Copilot Chat (not markdown files), use the native tool for:

• Interactive exploration: Pan, zoom, and full-screen viewing
• Immediate feedback: See diagrams without switching to markdown preview
• Iterative refinement: Quick edits with instant re-render
• Copy source: Extract the Mermaid code for documentation

Usage Pattern

User: Create a sequence diagram showing OAuth flow

Alex: [uses renderMermaidDiagram tool]
       → Interactive diagram appears in chat
       → User can pan/zoom/fullscreen
       → "Copy source" extracts code for docs

When NOT to Use

• Documentation authoring: Use markdown code blocks for .md files
• GitHub rendering: Embed Mermaid in markdown for native GitHub support
• Presentations: Export to image formats or use D2

Combined Workflow

1. Design in chat: Use renderMermaidDiagram for rapid iteration
2. Finalize: Copy the Mermaid source code
3. Document: Paste into markdown file with ```mermaid code fence

Assets

Setup: Copy CSS to .vscode/, add "markdown.styles": [".vscode/markdown-light.css"] to settings.

Mermaid Config: Run the "Polish Mermaid Setup" prompt to configure Mermaid rendering for your VS Code environment.

Markdown Best Practices

Document Structure Template

# Title

> Brief description or tagline

---

## Overview

Introductory paragraph explaining the purpose.

---

## Section 1

Content with proper formatting.

### Subsection 1.1

More detailed content.

---

## Tables

**Table N:** *Description of what the table shows*

| Column 1 | Column 2 |
| -------- | -------- |
| Data     | Data     |

---

## Diagrams

` ` `mermaid
flowchart LR
    A --> B
` ` `

**Figure N:** *Description of what the diagram shows*

---

*Footer or closing statement*

Figure and Table Conventions

Mandatory Labeling: Every diagram and table MUST have a label:

**Figure 1:** *Description in italics*
**Table 1:** *Description in italics*

• Numbering: Sequential within document, reset per document
• Placement: Label immediately follows the diagram/table block

🏷️ Shields.io Badges

Badge Anatomy

Badges use Shields.io - a free service for generating status badges.

URL Structure:

https://img.shields.io/badge/{LABEL}-{MESSAGE}-{COLOR}?{OPTIONS}

Markdown Syntax:

[![Alt Text](https://img.shields.io/badge/Label-Message-color?options)](#)

Style Options

Common Color Names

Custom Hex: Use any hex without # → ?color=1f2328

Adding Icons (Simple Icons)

Shields.io integrates with Simple Icons for brand logos:

[![VS Code](https://img.shields.io/badge/VS_Code-Extension-blue?logo=visualstudiocode&logoColor=white)](#)

Parameters:

• logo=iconname - Icon from Simple Icons (lowercase, no spaces)
• logoColor=white - Icon color (usually white for dark backgrounds)

Badge Templates

Version Badge:

[![Version](https://img.shields.io/badge/Version-1.0.0-gold?style=for-the-badge&logo=trophy&logoColor=white)](#)

Domain/Category Badge:

[![Domain](https://img.shields.io/badge/Domain-DIAGRAMMING-blue?style=for-the-badge&logo=graduation-cap&logoColor=white)](#)

Quality Badge:

[![Quality](https://img.shields.io/badge/Quality-Enterprise_Grade-green?style=for-the-badge&logo=shield-alt&logoColor=white)](#)

Status Badge:

[![Status](https://img.shields.io/badge/Status-Active-brightgreen?style=for-the-badge)](#)
[![Status](https://img.shields.io/badge/Status-Beta-orange?style=for-the-badge)](#)
[![Status](https://img.shields.io/badge/Status-Deprecated-red?style=for-the-badge)](#)

Document Header Pattern

Professional documents use a badge row at the top:

# Document Title

[![Version](https://img.shields.io/badge/Version-1.0.0-gold?style=for-the-badge&logo=trophy&logoColor=white)](#) [![Domain](https://img.shields.io/badge/Domain-TOPIC-blue?style=for-the-badge)](#)

> Description tagline

---

Special Characters in Badges

Dynamic Badges (Advanced)

For live data from repos:

[![GitHub Stars](https://img.shields.io/github/stars/owner/repo?style=for-the-badge)](#)
[![NPM Version](https://img.shields.io/npm/v/package-name?style=for-the-badge)](#)
[![Build Status](https://img.shields.io/github/actions/workflow/status/owner/repo/ci.yml?style=for-the-badge)](#)

Emoji Usage

Best Practice: Use actual emoji characters, not HTML entities or unicode escapes.

🎯 Diagram Tool Selection Framework

Step 1: Identify Your Communication Goal

Step 2: Consider Your Audience

Step 3: Consider Platform

Quick Decision Tree

Need diagram? → What are you showing?
├── Process/Workflow → Mermaid Flowchart
├── System Architecture → Mermaid with subgraphs (or D2 for exec)
├── Relationships → Mermaid ER/Mindmap (or Graphviz for complex)
├── Time/Sequence → Mermaid Sequence/Gantt
└── Data/Metrics → Mermaid XY/Sankey/Quadrant

🛠️ Multi-Tool Ecosystem

Tool Comparison Matrix

VS Code Extension Setup

{
  "recommendations": [
    "bierner.markdown-mermaid",
    "vstirbu.vscode-mermaid-preview",
    "mermaidchart.vscode-mermaid-chart",
    "jebbs.plantuml",
    "joaompinto.vscode-graphviz",
    "terrastruct.d2",
    "shd101wyy.markdown-preview-enhanced",
    "yzane.markdown-pdf",
    "bierner.markdown-preview-github-styles"
  ]
}

Syntax Examples

PlantUML (Enterprise UML):

@startuml
!theme aws-orange
participant User
participant System
participant Database

User -> System: Request
System -> Database: Query
Database --> System: Response
System --> User: Result
@enduml

Graphviz DOT (Complex Networks):

digraph G {
    rankdir=TB;
    node [shape=box, style=filled, fillcolor=lightblue];
    A -> B;
    A -> C;
    B -> D;
    C -> D;
}

D2 (Modern Architecture):

users -> web_server: HTTPS requests
web_server -> database: SQL queries

users.style.fill: "#e1f5fe"
web_server.style.fill: "#f3e5f5"

🎨 Mermaid Diagram Reference

⚡ Quick Start — Pastel v2 Template

See the MANDATORY template at the top of this skill. That template is authoritative. This section is a quick reminder:

%%{init: {'theme': 'base', 'themeVariables': {'lineColor': '#57606a', 'primaryColor': '#ddf4ff', 'primaryBorderColor': '#0969da', 'primaryTextColor': '#1f2328', 'edgeLabelBackground': '#ffffff'}}}%%
flowchart LR
    A[Source]:::blue -->|transform| B[Process]:::purple --> C[Output]:::green

    classDef blue fill:#ddf4ff,color:#0550ae,stroke:#80ccff
    classDef green fill:#d3f5db,color:#1a7f37,stroke:#6fdd8b
    classDef purple fill:#d8b9ff,color:#6639ba,stroke:#bf8aff
    classDef gold fill:#fff8c5,color:#9a6700,stroke:#d4a72c
    classDef red fill:#ffebe9,color:#cf222e,stroke:#f5a3a3
    classDef neutral fill:#eaeef2,color:#24292f,stroke:#d0d7de

    linkStyle default stroke:#57606a,stroke-width:1.5px

Four things every diagram needs:

1. %%{init}%% directive with edgeLabelBackground: '#ffffff'
2. classDef or style for node colors
3. linkStyle default stroke:#57606a for arrow color
4. Edge labels |text| with white background (from init)

💡 For color theory and design principles, see the graphic-design skill. The palette values here come from that skill's color system, optimized for GitHub rendering.

Diagram Types

Node Shapes (Flowchart)

A[Rectangle]      B(Rounded)        C([Stadium])
D[[Subroutine]]   E[(Database)]     F((Circle))
G>Asymmetric]     H{Diamond}        I{{Hexagon}}
J[/Parallelogram/]

Edge Styles

A --> B           Standard arrow
A --- B           Line without arrow
A -.-> B          Dotted arrow
A ==> B           Thick arrow
A --"label"--> B  Labeled edge
A -->|"label"| B  Alternative label syntax

Color Palette (Legacy — GitHub-Compatible)

Note: Superseded by GitHub Pastel Palette v2 below. Kept for reference only.

GitHub Pastel Palette v2 (Default)

Higher contrast, better accessibility. Always use this palette for new diagrams.

Node Style Pattern: style NODE fill:#FILL,color:#TEXT,stroke:#STROKE

Arrow/Link Styling (CRITICAL for readability):

linkStyle default stroke:#57606a,stroke-width:1.5px

Complete Example:

%%{init: {'theme': 'base', 'themeVariables': {'lineColor': '#57606a', 'primaryColor': '#ddf4ff', 'primaryBorderColor': '#0969da', 'primaryTextColor': '#1f2328', 'edgeLabelBackground': '#ffffff'}}}%%
flowchart LR
    A[Source]:::blue -->|Transform| B[Target]:::green

    classDef blue fill:#ddf4ff,color:#0550ae,stroke:#80ccff
    classDef green fill:#d3f5db,color:#1a7f37,stroke:#6fdd8b

    linkStyle default stroke:#57606a,stroke-width:1.5px

Key Principles:

1. Light fills (#fff1e5, #ddf4ff) — Easy on the eyes
2. Medium text (#953800, #0550ae) — Readable but not harsh
3. Soft strokes matching fill family
4. Gray arrows (#57606a) — Neutral, doesn't compete with nodes
5. 1.5-2px stroke-width — Visible but not heavy
6. edgeLabelBackground: '#ffffff' — White background for readable edge labels

Fishbowl Pastel Palette (Alternative)

Softer palette with uniform dark text. Good for governance, compliance, and presentation diagrams.

Init directive (Fishbowl):

%%{init: {'theme': 'base', 'themeVariables': {
  'primaryColor': '#cce5ff',
  'primaryBorderColor': '#4a90d9',
  'primaryTextColor': '#333',
  'secondaryColor': '#e6d5f2',
  'tertiaryColor': '#c2f0d8',
  'lineColor': '#666',
  'edgeLabelBackground': '#ffffff'
}}}%%

When to choose Fishbowl over GitHub Pastel v2: Use Fishbowl when all nodes need equal visual weight (e.g., governance structures, compliance flows). Use GitHub Pastel v2 when nodes carry semantic meaning that should be color-coded by category.

Per-Diagram Theming (MANDATORY for consistency)

Add as FIRST line inside mermaid block:

Default init directive (GitHub Pastel v2):

%%{init: {'theme': 'base', 'themeVariables': {
  'primaryColor': '#ddf4ff',
  'primaryBorderColor': '#0969da',
  'primaryTextColor': '#1f2328',
  'lineColor': '#57606a',
  'edgeLabelBackground': '#ffffff'
}}}%%

Standard GitHub-compatible theme (legacy):

%%{init: {'theme': 'base', 'themeVariables': {
  'primaryColor': '#f6f8fa',
  'primaryBorderColor': '#d1d9e0',
  'primaryTextColor': '#1f2328',
  'lineColor': '#656d76',
  'edgeLabelBackground': '#ffffff'
}}}%%

Quadrant chart theme:

%%{init: {'theme': 'base', 'themeVariables': {
  'quadrant1Fill': '#d3f5db',
  'quadrant2Fill': '#fff8c5',
  'quadrant3Fill': '#ffebe9',
  'quadrant4Fill': '#ddf4ff',
  'quadrantPointFill': '#1f2328',
  'quadrantTitleFill': '#1f2328'
}}}%%

classDef Reusable Styles

Define style classes once and apply to multiple nodes. Cleaner than per-node style directives.

flowchart LR
    A[Source]:::input --> B[Process]:::action --> C[Output]:::success

    classDef input fill:#ddf4ff,color:#0550ae,stroke:#80ccff
    classDef action fill:#fff8c5,color:#9a6700,stroke:#d4a72c
    classDef success fill:#d3f5db,color:#1a7f37,stroke:#6fdd8b
    classDef error fill:#ffebe9,color:#cf222e,stroke:#f5a3a3
    classDef neutral fill:#eaeef2,color:#24292f,stroke:#d0d7de
    classDef special fill:#d8b9ff,color:#6639ba,stroke:#bf8aff
    classDef bronze fill:#fff1e5,color:#953800,stroke:#ffb77c

Pastel v2 classDef Quick Reference (copy-paste ready):

classDef blue fill:#ddf4ff,color:#0550ae,stroke:#80ccff
classDef green fill:#d3f5db,color:#1a7f37,stroke:#6fdd8b
classDef purple fill:#d8b9ff,color:#6639ba,stroke:#bf8aff
classDef gold fill:#fff8c5,color:#9a6700,stroke:#d4a72c
classDef red fill:#ffebe9,color:#cf222e,stroke:#f5a3a3
classDef bronze fill:#fff1e5,color:#953800,stroke:#ffb77c
classDef neutral fill:#eaeef2,color:#24292f,stroke:#d0d7de

Apply to multiple nodes: class A,B,C blue

Apply inline: A[Label]:::blue

Subgraph Styling

Style subgraph backgrounds with the style directive using the subgraph ID:

flowchart LR
    subgraph SG1["Phase 1"]
        direction TB
        A --> B
    end
    subgraph SG2["Phase 2"]
        direction TB
        C --> D
    end

    style SG1 fill:#ddf4ff,stroke:#80ccff,color:#0550ae
    style SG2 fill:#d3f5db,stroke:#6fdd8b,color:#1a7f37

Key: Use fill for background, keep it light. The color property sets the title text color.

Gantt Chart Theming

Gantt charts use different theme variables than flowcharts:

  'taskBkgColor': '#ddf4ff',
  'activeTaskBkgColor': '#d3f5db',
  'activeTaskBorderColor': '#6fdd8b',
  'doneTaskBkgColor': '#eaeef2',
  'doneTaskBorderColor': '#d0d7de',
  'critBkgColor': '#ffebe9',
  'critBorderColor': '#f5a3a3',
  'todayLineColor': '#cf222e',
  'gridColor': '#d0d7de',
  'sectionBkgColor': '#f6f8fa',
  'altSectionBkgColor': '#ffffff',
  'taskTextColor': '#24292f',
  'sectionBkgColor2': '#f6f8fa'
}}}%%

Section formatting: Gantt sections inherit alternating background colors. Use section keyword to group related tasks:

gantt
    title Project Timeline
    dateFormat YYYY-MM-DD
    section Phase 1
    Task A :done, a1, 2026-01-01, 14d
    Task B :active, a2, after a1, 7d
    section Phase 2
    Task C :crit, a3, after a2, 10d

Sequence Diagram Theming

  'actorBkg': '#ddf4ff',
  'actorBorder': '#80ccff',
  'actorTextColor': '#0550ae',
  'activationBkgColor': '#d3f5db',
  'activationBorderColor': '#6fdd8b',
  'signalColor': '#57606a',
  'labelBoxBkgColor': '#fff8c5',
  'labelTextColor': '#9a6700',
  'noteBkgColor': '#fff8c5',
  'noteTextColor': '#9a6700',
  'noteBorderColor': '#d4a72c'
}}}%%

🎨 Visual Design Principles

Color Psychology in Diagrams

Diagram Effectiveness Criteria

• Clarity: Audience understands in 30 seconds
• Accuracy: Correctly represents the system/process
• Completeness: All essential elements, no clutter
• Consistency: Follows visual conventions
• Maintainability: Easy to update

Accessibility Standards

• Provide alternative text descriptions
• Use color-blind friendly palettes
• Ensure sufficient contrast
• Don't rely on color alone for meaning

⚠️ Common Pitfalls & Solutions

Unicode Escape Sequences (Broken Emojis)

Problem: Emojis stored as \ud83d\udcbb display as raw codes instead of 💻

Detection (PowerShell):

Get-ChildItem -Recurse -Filter "*.md" | Select-String -Pattern '\\u[0-9a-fA-F]{4}' | Group-Object Path

Prevention (VS Code settings):

{
    "files.encoding": "utf8",
    "files.autoGuessEncoding": false
}

Emoji Mapping Table

Edge Label Dark Background

Problem: Arrow labels (|text|) appear with dark boxes in VS Code dark mode or break rendering

Root cause: Missing or incorrect edgeLabelBackground settings.

Fix: Always include edgeLabelBackground: '#ffffff' in your init directive:

%%{init: {'theme': 'base', 'themeVariables': {
  'primaryColor': '#ddf4ff',
  'lineColor': '#57606a',
  'edgeLabelBackground': '#ffffff'
}}}%%

flowchart LR
    A -->|label text| B

This provides a clean white background for edge labels, ensuring readability on any rendering surface.

⚠️ Never use theme: 'dark' — use theme: 'base' with the pastel palette instead.

Multi-Line Node Labels (\n vs <br/>)

Problem: \n in node labels renders as a literal backslash-n in VS Code and some Mermaid versions:

❌ A["First line\nSecond line"]   ← may render as "First line\nSecond line"
✅ A["First line<br/>Second line"] ← always works

Rule: Always use <br/> for multi-line node labels in flowcharts.

Dark Mermaid Backgrounds

Problem: Diagrams have dark backgrounds in VS Code preview

Solution 2: Apply included markdown-light.css via settings

Disproportionate Diagram Layouts (Too Wide/Too Tall)

Problem: Diagrams become too wide (horizontal) or too tall (vertical), causing poor readability

Detection: Look for diagrams where one dimension is 3x+ the other

Pattern: Use opposing directions for outer flowchart vs. inner subgraphs:

%% Pattern 1: TD outer with LR inner (vertical stack of horizontal lanes)
flowchart TD
    subgraph Phase1["Phase 1"]
        direction LR
        A --> B --> C
    end
    subgraph Phase2["Phase 2"]
        direction LR
        D --> E --> F
    end

%% Pattern 2: LR outer with TB inner (horizontal flow of vertical stacks)
flowchart LR
    subgraph Group1["Group 1"]
        direction TB
        A --> B --> C
    end
    subgraph Group2["Group 2"]
        direction TB
        D --> E --> F
    end

Key Rules:

Anti-Pattern 1: Single subgraph with opposing direction has no effect (nothing to stack)

%% WRONG - single subgraph, direction LR does nothing useful
flowchart TD
    subgraph Only["Only Subgraph"]
        direction LR
        A --> B --> C --> D --> E  %% Still very wide!
    end

%% RIGHT - break into multiple subgraphs
flowchart TD
    subgraph Phase1["Setup"]
        direction LR
        A --> B
    end
    subgraph Phase2["Execute"]
        direction LR
        C --> D
    end

Anti-Pattern 2: Cross-subgraph edges defined inside subgraphs (causes layout confusion)

%% WRONG - edge to next subgraph defined inside source subgraph
flowchart TD
    subgraph Phase1["Setup"]
        direction LR
        A --> B
        B --> C  %% C is in Phase2!
    end
    subgraph Phase2["Execute"]
        direction LR
        C --> D
    end

%% RIGHT - cross-subgraph edges defined outside all subgraphs
flowchart TD
    subgraph Phase1["Setup"]
        direction LR
        A --> B
    end
    subgraph Phase2["Execute"]
        direction LR
        C --> D
    end
    B --> C  %% Cross-subgraph edge outside
    subgraph Phase3["Complete"]
        direction LR
        E
    end

Anti-Pattern 3: Independent subgraphs without connections default to vertical stacking

%% WRONG - no connections between subgraphs, ignores LR direction
flowchart LR
    subgraph A["Group A"]
        direction TB
        A1 --> A2
    end
    subgraph B["Group B"]
        direction TB
        B1 --> B2
    end
    %% Result: Groups stack vertically despite LR!

%% RIGHT - invisible links force horizontal layout
flowchart LR
    subgraph A["Group A"]
        direction TB
        A1 --> A2
    end
    subgraph B["Group B"]
        direction TB
        B1 --> B2
    end
    A ~~~ B  %% Invisible link forces LR arrangement

Named Layout Patterns

Use these named patterns for consistent, well-proportioned diagrams. Each combines an outer flowchart direction with inner subgraph directions.

Medallion Pattern (TD + LR)

Use when: Phases/layers stack vertically, each containing a horizontal flow.

flowchart TD
    subgraph Phase1["Phase 1: Ingestion"]
        direction LR
        A[Source] --> B[Validate] --> C[Store]
    end
    subgraph Phase2["Phase 2: Processing"]
        direction LR
        D[Load] --> E[Transform] --> F[Enrich]
    end
    Phase1 --> Phase2

Result: Compact rectangle. Good for pipelines, ETL stages, layered architectures.

Lineage Pattern (LR + TB)

Use when: Groups flow left-to-right, each containing a vertical stack.

flowchart LR
    subgraph Cluster1["Input"]
        direction TB
        A1[Raw] --> A2[Clean]
    end
    subgraph Cluster2["Process"]
        direction TB
        B1[Compute] --> B2[Validate]
    end
    subgraph Cluster3["Output"]
        direction TB
        C1[Format] --> C2[Deliver]
    end
    Cluster1 --> Cluster2 --> Cluster3

Result: Wide timeline-like layout. Good for data lineage, system boundaries, progression.

Pipeline Pattern (LR + LR)

Use when: Everything flows left-to-right (flat pipeline, no vertical stacking needed).

flowchart LR
    A[Input] --> B[Stage 1] --> C[Stage 2] --> D[Output]

Result: Simple horizontal chain. Good for CI/CD, request flows, simple sequences.

Pattern Decision Matrix

Independent Subgraphs (Invisible Links)

When subgraphs have no logical connections between them, Mermaid ignores the outer direction and stacks them vertically by default. Fix with invisible links (~~~):

flowchart LR
    subgraph A["Group A"]
        direction TB
        A1 --> A2
    end
    subgraph B["Group B"]
        direction TB
        B1 --> B2
    end
    A ~~~ B  %% Forces horizontal arrangement per outer LR

Rule: Always add ~~~ between independent subgraphs to enforce the outer direction.

Multiple independent groups: Chain invisible links: A ~~~ B ~~~ C ~~~ D

Subgraph Title Truncation (VS Code Only)

Problem: Subgraph titles get truncated in VS Code preview

Note: This is a VS Code Mermaid renderer bug. GitHub renders correctly.

Root Cause: VS Code calculates subgraph width from content nodes, NOT title text.

Workaround: Make content nodes wider so the subgraph expands:

%% BAD in VS Code - narrow nodes clip title
subgraph CONSCIOUS["🌟 Conscious Mind"]
    A["Chat"]
    B["Commands"]
end

%% GOOD - descriptive labels force wider box
subgraph CONSCIOUS["🌟 Conscious Mind"]
    A["💬 Chat Participant"]
    B["⚡ VS Code Commands"]
end

Mermaid Parse Errors

Problem: Nested quotes, parentheses, or reserved words cause cryptic parse errors

Rule 1: Don't nest quotes inside quoted node labels

%% ❌ FAILS - nested quotes
["Return with<br/>"🌐 Results<br/>(Info)"]

%% ✅ WORKS - no nested quotes
["🌐 Return Results<br/>Info"]

Rule 2: Avoid HTML tags inside node labels (some renderers choke on them)

%% ❌ RISKY - <i> tag may break parsing
CFG["config.json<br/><i>inert — rarely traversed</i>"]

%% ✅ SAFE - plain text with em dash
CFG["config.json — inert, rarely traversed"]

Rule 3: Avoid em dashes (—) in subgraph titles (some parsers treat them as operators)

%% ❌ RISKY - em dash in subgraph title
subgraph P1["Phase 1 — Compiled Graph"]

%% ✅ SAFE - colon or hyphen instead
subgraph P1["Phase 1: Compiled Graph"]
subgraph P1["Phase 1 - Compiled Graph"]

Rule 4: Place style directives for subgraphs outside the subgraph block

%% ❌ FAILS in some renderers - style inside subgraph
subgraph SG["My Group"]
    style SG fill:#ddf4ff,stroke:#80ccff
    direction TB
    A --> B
end

%% ✅ WORKS everywhere - style after all subgraphs
subgraph SG["My Group"]
    direction TB
    A --> B
end
style SG fill:#ddf4ff,stroke:#80ccff

classDiagram-Specific Pitfalls

Critical: classDiagram has a different parser than flowchart. Syntax that works in flowcharts often breaks in class diagrams. Never assume cross-compatibility.

Reserved Keyword Collisions

classDiagram reserves more keywords than flowcharts. Using them as classDef names or class annotations collides with the parser.

%% ❌ FAILS - "abstract" is a classDiagram keyword
classDef abstract fill:#ddf4ff,stroke:#80ccff

%% ❌ ALSO FAILS - "abstract" parsed as <<abstract>> annotation
class MemorySystem abstract

%% ✅ WORKS - renamed classDef avoids collision
classDef base fill:#ddf4ff,stroke:#80ccff
class MemorySystem base

Comma-Separated Class Lists

class A,B,C styleName syntax works in flowchart but NOT in classDiagram. Each class needs its own class X styleName line.

%% ❌ FAILS in classDiagram - comma syntax not supported
class UserStore,SessionStore,CacheStore storage

%% ✅ WORKS - one line per class
class UserStore storage
class SessionStore storage
class CacheStore storage

Note: In flowchart, class A,B,C styleName is valid (skillCatalog.ts uses this correctly).

classDef Property Limitations

classDef in classDiagram only supports SVG presentation attributes. CSS text properties are silently ignored.

%% ❌ SILENTLY IGNORED - font-weight does nothing
classDef important fill:#fff3e0,stroke:#ef6c00,font-weight:bold

%% ✅ WORKS - use only SVG attributes
classDef important fill:#fff3e0,stroke:#ef6c00,stroke-width:2px

stroke-dasharray Space Parsing

The space in stroke-dasharray:6 3 breaks Mermaid's comma-delimited property parser in classDiagram. In flowchart it may work.

%% ❌ FAILS in classDiagram - space in value breaks parser
classDef dashed stroke-dasharray:6 3

%% ⚠️ MAY WORK - single value, no space
classDef dashed stroke-dasharray:5

%% ✅ SAFE in flowchart - space tolerated
classDef dashed stroke-dasharray:5 5

Rule: In classDiagram, avoid stroke-dasharray entirely or use a single integer value. In flowchart, stroke-dasharray:5 5 works.

Decimal stroke-width

Decimal values like stroke-width:2.5px can cause inconsistent rendering across Mermaid renderers.

%% ⚠️ INCONSISTENT - decimal may not render
classDef thick stroke-width:2.5px

%% ✅ SAFE - integer values
classDef thick stroke-width:2px
classDef thicker stroke-width:3px

architecture-beta Pitfalls

Critical: architecture-beta is an experimental diagram type with a much stricter tokenizer than mature types. Assume nothing works unless proven.

Spaces in Bracket Labels

Labels in [...] do not support spaces. Multi-word labels cause the parser to treat each word as a separate token.

%% ❌ FAILS - space in bracket label
service api(server)[API Gateway]

%% ✅ WORKS - no spaces (use underscores or camelCase)
service api(server)[APIGateway]
service api(server)[Api_Gateway]

Hyphens in Labels

Hyphens like 4-3-3 are parsed as edge connectors (-- or -), not literal characters. There is no escape mechanism.

%% ❌ FAILS - hyphens parsed as edge syntax
service formation(server)[4-3-3]

%% ✅ WORKS - no hyphens
service formation(server)[Formation433]

Reserved IDs

Common programming keywords may conflict with the parser:

Comments May Not Work

%% comments that work in all other diagram types may cause parse errors in architecture-beta.

%% ❌ MAY FAIL - standard comments
%% This is my architecture
architecture-beta

%% ✅ SAFE - no comments at all
architecture-beta

Icons Only on service, Not group

(icon) syntax only works on service declarations. Using it on group causes a parse error.

%% ❌ FAILS - group does not accept (icon)
group cloud(cloud)[Infra

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