Mermaid Diagram Skill for Claude

Mermaid Diagram Generator

Generate high-quality Mermaid diagram code based on user requirements, with file output and verification.

Constants

• OUTPUT_DIR = figures/ — Output directory for all generated files
• MAX_ITERATIONS = 3 — Maximum refinement rounds for syntax errors

Workflow: MUST EXECUTE ALL STEPS

Step 0: Pre-flight Check

# Create output directory
mkdir -p figures

Step 1: Understand Requirements & Select Diagram Type

Parse the input: $ARGUMENTS

• Analyze user description to determine the most suitable diagram type
• Read the corresponding syntax reference documentation (see Diagram Type Reference below)
• If the diagram involves mathematical notation (formulas, equations, Greek letters, subscripts, superscripts, fractions, matrices, etc.), apply the math syntax rules from the Math Formulas in Diagrams section below
• Identify all components, connections, and data flow
• Plan the diagram structure

Step 2: Read Documentation

Select the appropriate diagram type based on the use case. Use your built-in knowledge of Mermaid syntax, or fetch up-to-date docs via the context7 MCP server if needed.

| Type | Use Cases |

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

| Flowchart | Processes, decisions, steps |

| Sequence Diagram | Interactions, messaging, API calls |

| Class Diagram | Class structure, inheritance, associations |

| State Diagram | State machines, state transitions |

| ER Diagram | Database design, entity relationships |

| Gantt Chart | Project planning, timelines |

| Pie Chart | Proportions, distributions |

| Mindmap | Hierarchical structures, knowledge graphs |

| Timeline | Historical events, milestones |

| Git Graph | Branches, merges, versions |

| Quadrant Chart | Four-quadrant analysis |

| Requirement Diagram | Requirements traceability |

| C4 Diagram | System architecture (C4 model) |

| Sankey Diagram | Flow, conversions |

| XY Chart | Line charts, bar charts |

| Block Diagram | System components, modules |

| Packet Diagram | Network protocols, data structures |

| Kanban | Task management, workflows |

| Architecture Diagram | System architecture |

| Radar Chart | Multi-dimensional comparison |

| Treemap | Hierarchical data visualization |

| User Journey | User experience flows |

| ZenUML | Sequence diagrams (code style) |

Configuration & Themes

• Theming - Custom colors and styles
• Directives - Diagram-level configuration
• Layouts - Layout direction and spacing
• Configuration - Global settings
• Math - LaTeX math support (see Math Formulas in Diagrams section below)

Step 3: Generate Mermaid Code & Save Files

Generate the Mermaid code following the reference specification, then save TWO files:

File 1: figures/<diagram-name>.mmd — Raw Mermaid source

The .mmd file contains ONLY the raw Mermaid code (no markdown fences). Example:

flowchart TD
    A[Start] --> B{Condition}
    B -->|Yes| C[Execute]
    B -->|No| D[End]
    C --> D

File 2: figures/<diagram-name>.md — Markdown with embedded Mermaid

The .md file wraps the same code in a mermaid code block for preview rendering, plus a title and description. Example:

# Diagram Title

Brief description of what this diagram shows.

​```mermaid
flowchart TD
    A[Start] --> B{Condition}
    B -->|Yes| C[Execute]
    B -->|No| D[End]
    C --> D
​```

Naming convention: Use a descriptive kebab-case name derived from the user's request (e.g., auth-flow, system-architecture, database-er).

Step 4: Verify Mermaid Syntax (MANDATORY)

Claude MUST verify the generated Mermaid code by running the Mermaid CLI (mmdc).

# Check if mermaid-cli is available
if command -v mmdc &> /dev/null; then
    # Render to PNG to verify syntax is correct
    mmdc -i figures/<diagram-name>.mmd -o figures/<diagram-name>.png -b transparent
    echo "✅ Syntax valid — PNG rendered to figures/<diagram-name>.png"
else
    # Try npx as fallback
    npx -y @mermaid-js/mermaid-cli@latest -i figures/<diagram-name>.mmd -o figures/<diagram-name>.png -b transparent
    echo "✅ Syntax valid — PNG rendered to figures/<diagram-name>.png"
fi

If the verification fails:

• Read the error message carefully
• Fix the syntax issue in both .mmd and .md files
• Re-run verification
• Repeat up to MAX_ITERATIONS (3) times

Step 5: Claude STRICT Visual Review & Scoring (MANDATORY)

After successful rendering, Claude MUST read the generated PNG and perform a STRICT review:

## Claude's STRICT Review of <diagram-name>

### What I See
[Describe the rendered diagram in DETAIL - every block, every arrow, every label]

### Files Generated
- `figures/<diagram-name>.mmd` — Raw Mermaid source
- `figures/<diagram-name>.md` — Markdown with embedded diagram
- `figures/<diagram-name>.png` — Rendered PNG (if mmdc available)

### ═══════════════════════════════════════════════════════════════
### STRICT VERIFICATION CHECKLIST (ALL must pass for score ≥ 9)
### ═══════════════════════════════════════════════════════════════

#### A. File Correctness
- [ ] `.mmd` file contains valid Mermaid syntax (no markdown fences)
- [ ] `.md` file has the mermaid code wrapped in ```mermaid``` fences
- [ ] `.mmd` and `.md` contain IDENTICAL Mermaid code
- [ ] Diagram renders without errors (via mmdc)

#### B. Arrow Correctness Verification (CRITICAL - any failure = score ≤ 6)
Check EACH arrow:
- [ ] Arrow 1: [Source] → [Target] — Does it point to the CORRECT target?
- [ ] Arrow 2: [Source] → [Target] — Does it point to the CORRECT target?
- [ ] ... (check ALL arrows)

#### C. Block Content Verification (any failure = score ≤ 7)
Check EACH block/node:
- [ ] Block 1 "[Name]": Has correct label? Content correct?
- [ ] Block 2 "[Name]": Has correct label? Content correct?
- [ ] ... (check ALL blocks)

#### D. Completeness
- [ ] All components from user requirements are present
- [ ] All connections/arrows are correct
- [ ] Node labels are meaningful and match requirements

#### E. Visual Quality
- [ ] Layout is clean and readable
- [ ] Color scheme is professional (not rainbow)
- [ ] Text is readable at normal zoom
- [ ] Proper spacing (not cramped, not sparse)
- [ ] Data flow is traceable in 5 seconds

### ═══════════════════════════════════════════════════════════════

### Issues Found (BE SPECIFIC)
1. [Issue 1]: [EXACTLY what is wrong] → [How to fix]
2. [Issue 2]: [EXACTLY what is wrong] → [How to fix]

### Score: X/10

### Score Breakdown Guide:
- **10**: Perfect. No issues. Publication-ready.
- **9**: Excellent. Minor issues that don't affect understanding.
- **8**: Good but has noticeable issues (layout, styling).
- **7**: Usable but has clear problems (wrong arrows, missing labels).
- **6**: Has arrow direction errors or missing major components.
- **1-5**: Major issues. Unacceptable.

### Verdict
[ ] ACCEPT (score ≥ 9 AND all critical checks pass)
[ ] FIX (score < 9 OR any critical check fails — list EXACT fixes needed)

If FIX: apply corrections to both .mmd and .md files, re-render, and re-verify. Loop until ACCEPT or MAX_ITERATIONS reached.

Step 6: Final Output Summary

When accepted, present to user:

✅ Mermaid diagram generated successfully!

Files:
  figures/<diagram-name>.mmd  — Raw Mermaid source (use with mmdc, editors, CI)
  figures/<diagram-name>.md   — Markdown preview (renders on GitHub, VS Code, etc.)
  figures/<diagram-name>.png  — Rendered image (if mmdc was available)

To re-render manually:
  mmdc -i figures/<diagram-name>.mmd -o figures/<diagram-name>.png

Architecture Diagram Best Practices

When generating architecture-beta diagrams, apply these layout techniques for complex diagrams:

Use Junctions for Layout Control

Think of the diagram as an invisible grid. Use junction nodes as virtual anchor points on that grid to precisely control where each component is placed. This is especially useful when a direct edge between two services produces unexpected positioning.

Instead of connecting services directly:

lb:R --> L:scim
lb:R --> L:webapi

Route through junctions to control vertical/horizontal placement:

junction j_lb_r
lb:R -- L:j_lb_r
junction j_scim_l
j_lb_r:T -- B:j_scim_l
j_scim_l:R --> L:scim
junction j_webapi_l
j_lb_r:B -- T:j_webapi_l
j_webapi_l:R --> L:webapi

Place junctions on all four sides of components to anchor them logically on the grid.

Use Edges out of Groups for Floating Components

For services that have no logical connection to other nodes (e.g. a deployment tool, a monitoring agent), use a junction combined with the {group} modifier to position them without adding a semantically incorrect edge:

junction j_acd_t
j_algolia_proc_b{group}:B -- T:j_acd_t
j_acd_t:B -- T:acd

This anchors acd below its intended neighbor without implying a real relationship.

CVPR/ICLR/NeurIPS Style Guide (for Academic Diagrams)

When the diagram is intended for academic papers, apply these style standards:

Visual Standards

• Clean white background — No decorative patterns or gradients (unless subtle)
• Sans-serif fonts — Arial, Helvetica, or Computer Modern; minimum 14pt
• Subtle color palette — Not rainbow colors; use 3-5 coordinated colors
• Print-friendly — Must be readable in grayscale (many reviewers print papers)
• Professional borders — Thin (2-3px), solid colors, not flashy

Layout Standards

• Horizontal flow — Left-to-right is the standard for pipelines
• Clear grouping — Use subtle background boxes to group related modules
• Consistent sizing — Similar components should have similar sizes
• Balanced whitespace — Not cramped, not sparse

Arrow Standards (MOST CRITICAL)

• Thick strokes — 4-6px minimum (thin arrows disappear when printed)
• Clear arrowheads — Large, filled triangular heads
• Dark colors — Black or dark gray (#333333); avoid colored arrows
• Labeled — Every arrow should indicate what data flows through it
• No crossings — Reorganize layout to avoid arrow crossings
• CORRECT DIRECTION — Arrows must point to the RIGHT target!

Color Palette (Academic Professional)

• Inputs: Green (#10B981 / #34D399)
• Encoders: Blue (#2563EB / #3B82F6)
• Fusion: Purple (#7C3AED / #8B5CF6)
• Outputs: Orange (#EA580C / #F97316)
• Arrows: Black or dark gray (#333333 / #1F2937)
• Background: Pure white (#FFFFFF)

What to AVOID

• Rainbow color schemes (too many colors)
• Thin, hairline arrows
• Heavy drop shadows or glowing effects
• 3D effects / perspective
• Excessive decorative icons
• Small text that's unreadable when printed

Math Formulas in Diagrams (KaTeX)

Mermaid supports rendering mathematical expressions via KaTeX (v10.9.0+). When the diagram content involves math (formulas, equations, Greek letters, subscripts/superscripts, fractions, matrices, operators, etc.), use KaTeX notation instead of plain-text approximations.

Supported Diagram Types for Math

Math rendering with $$...$$ is supported in:

• Flowcharts (flowchart / graph) — in node labels and edge labels
• Sequence Diagrams — in participant aliases, messages, and notes

Syntax Rules

• Wrap math expressions in $$ delimiters inside quoted strings:

   A["$$x^2$$"] -->|"$$\sqrt{x+3}$$"| B("$$\frac{1}{2}$$")

• Node labels with math MUST be quoted — use ["$$...$$"] or ("$$...$$"):

   scaledDot["$$\text{softmax}\left(\frac{QK^T}{\sqrt{d_k}}\right)V$$"]

• Mix text and math by placing $$ only around the math portion:

   layer1["Linear Layer $$W_1 x + b_1$$"]

• Use \text{} for non-math text inside a $$ block:

   node["$$\text{Attention}(Q, K, V)$$"]

Common Math Patterns for ML/Science Diagrams

| Concept | KaTeX Syntax | Renders As |

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

| Subscript | $$W_Q$$ | W_Q |

| Superscript | $$x^2$$ | x² |

| Fraction | $$\frac{QK^T}{\sqrt{d_k}}$$ | QK^T / sqrt(d_k) |

| Greek letters | $$\alpha, \beta, \gamma$$ | α, β, γ |

| Square root | $$\sqrt{d_k}$$ | √d_k |

| Summation | $$\sum_{i=1}^{n} x_i$$ | Σx_i |

| Matrix | $$\begin{bmatrix} a & b \\ c & d \end{bmatrix}$$ | 2x2 matrix |

| Softmax | $$\text{softmax}(z_i)$$ | softmax(z_i) |

| Norm | $$\|\|x\|\|_2$$ | ‖x‖₂ |

| Hat/tilde | $$\hat{y}, \tilde{x}$$ | ŷ, x̃ |

Example: Attention Mechanism with Math

flowchart TD
    Q["$$Q \in \mathbb{R}^{n \times d_k}$$"]
    K["$$K \in \mathbb{R}^{n \times d_k}$$"]
    V["$$V \in \mathbb{R}^{n \times d_v}$$"]
    scores["$$\frac{QK^T}{\sqrt{d_k}}$$"]
    softmax["$$\text{softmax}(\cdot)$$"]
    output["$$\text{Attention}(Q,K,V)$$"]

    Q --> scores
    K --> scores
    scores --> softmax
    softmax --> weighted["$$\alpha V$$"]
    V --> weighted
    weighted --> output

When to Use Math vs Plain Text

• Use math when the diagram is for academic/technical audiences and precision matters (papers, lectures, technical docs)
• Use plain text (<br/> for line breaks) when the diagram is for general audiences or when math would add visual clutter without improving clarity
• Default behavior: If the user's request contains mathematical notation, equations, or Greek symbols, automatically use KaTeX math rendering. Otherwise, use plain text labels.

Gotchas

• The $$ delimiters must be inside quoted strings — unquoted $$ will break parsing
• Backslashes in KaTeX (\frac, \sqrt, etc.) work normally in Mermaid strings
• Very long formulas may overflow node boxes — break them with \\ (newline in KaTeX) or simplify
• Always verify rendering with mmdc — some KaTeX expressions may not render in all environments

Code Quality Rules

Generated Mermaid code MUST:

• Have correct syntax that renders directly
• Have clear structure with proper line breaks and indentation
• Use semantic node naming (not A, B, C — use authServer, userDB, etc.)
• Include styling when needed to improve visual appearance
• Use <br/> for line breaks inside node labels — never use \n, which renders as literal text
• Avoid special characters in labels that break Mermaid parsing (wrap in quotes if needed)

Output Structure

figures/
├── <diagram-name>.mmd    # Raw Mermaid source (no markdown fences)
├── <diagram-name>.md     # Markdown with embedded mermaid block
└── <diagram-name>.png    # Rendered PNG (if mmdc available)

Key Rules (MUST FOLLOW)

• ALWAYS save files to figures/ directory — Never just output code in chat
• ALWAYS generate BOTH .mmd and .md files — They must contain identical Mermaid code
• ALWAYS read the reference documentation before generating code for a diagram type
• ALWAYS verify syntax — Run mmdc or manually validate before accepting
• ALWAYS review the rendered PNG — Read the image and perform STRICT scoring
• NEVER accept score < 9 — Keep refining until excellence
• VERIFY EVERY ARROW DIRECTION — Wrong direction = automatic fail (score ≤ 6)
• VERIFY EVERY BLOCK CONTENT — Wrong content = automatic fail (score ≤ 7)
• BE SPECIFIC in feedback — "Arrow from A to B points wrong" not "arrow is wrong"

10. FIX errors before accepting — Do not deliver broken diagrams

11. Use descriptive file names — kebab-case derived from the diagram content

User requirements: $ARGUMENTS