Mermaid Diagram Agent Skill

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 generated files
• MAX_ITERATIONS = 3 — Maximum refinement rounds for syntax or layout issues

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 the request and choose the most suitable diagram type
• Read the corresponding Mermaid syntax reference below
• If the diagram involves mathematical notation, apply the math syntax rules from the Math Formulas in Diagrams section
• Identify all components, connections, and data flow
• Plan the diagram structure before writing code

Step 2: Read Documentation

Select the appropriate diagram type. Use built-in Mermaid knowledge first; if external documentation is needed and your environment provides it, fetch the up-to-date syntax reference.

Configuration & Themes

Choose theme, colors, and layout before writing code. For academic diagrams, prefer clean white backgrounds, restrained colors, and readable labels over decorative styling.

| 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 |

| 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) |

Step 3: Generate Mermaid Code & Save Files

Generate the Mermaid code and save two files:

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

The .mmd file contains only raw Mermaid code, no markdown fences.

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

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

Diagram Title

Use a concise title in the .md wrapper that matches the generated diagram name.

Naming convention: use a descriptive kebab-case name derived from the request, such as auth-flow, system-architecture, or database-er.

Step 4: Verify Mermaid Syntax (MANDATORY)

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

Check if mermaid-cli is available

if command -v mmdc >/dev/null 2>&1; then
    mmdc -i figures/<diagram-name>.mmd -o figures/<diagram-name>.png -b transparent
    echo "Syntax valid — PNG rendered to figures/<diagram-name>.png"
else
    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 verification fails:

• Read the error carefully
• Fix the syntax issue in both .mmd and .md
• Re-run verification
• Repeat up to MAX_ITERATIONS

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

After successful rendering, Codex MUST read the generated PNG and perform a strict review:

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

### What I See
[Describe the rendered diagram in detail]

### Files Generated
- `figures/<diagram-name>.mmd`
- `figures/<diagram-name>.md`
- `figures/<diagram-name>.png`

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

#### A. File Correctness
- [ ] `.mmd` contains valid Mermaid syntax
- [ ] `.md` wraps the Mermaid code in ```mermaid fences
- [ ] `.mmd` and `.md` contain identical Mermaid code
- [ ] Diagram renders without errors

ASCII alias for automated checks: score >= 9.

#### B. Arrow Correctness Verification (CRITICAL - any failure = score ≤ 6)
ASCII alias for automated checks: CRITICAL - any failure = score <= 6.

- [ ] Every arrow points to the correct target

#### C. Block Content Verification (any failure = score ≤ 7)
ASCII alias for automated checks: any failure = score <= 7.

- [ ] Every block label is correct
- [ ] Every block contains the intended content

#### D. Completeness
- [ ] All required components are present
- [ ] All required connections are present
- [ ] Labels are meaningful and match the request

#### E. Visual Quality
- [ ] Layout is clean and readable
- [ ] Colors are professional
- [ ] Text is readable at normal zoom
- [ ] Spacing is balanced
- [ ] Data flow is understandable within 5 seconds

### ═══════════════════════════════════════════════════════════════
### Issues Found (BE SPECIFIC)
1. [issue] -> [fix]

### Score: X/10

### Score Breakdown Guide:
- 10: correct, readable, publication-ready
- 9: minor polish only
- 8: usable but one visual/layout weakness remains
- 7: one content or block-label weakness remains
- 6 or below: arrow direction, missing component, syntax, or semantic error

### Verdict
- [ ] ACCEPT
- [ ] FIX

If the verdict is FIX, apply corrections to both .mmd and .md, re-render, and re-review until ACCEPT or MAX_ITERATIONS is reached.

Step 6: Final Output Summary

When accepted, present:

Mermaid diagram generated successfully.

Files:
  figures/<diagram-name>.mmd
  figures/<diagram-name>.md
  figures/<diagram-name>.png

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 placement. This is especially useful when a direct edge produces unexpected positioning.

Instead of connecting services directly:

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

Route through junctions:

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

Use Edges out of Groups for Floating Components

For services that have no real logical connection but still need stable placement, use a junction combined with {group} to anchor them without inventing a semantic edge.

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
• Sans-serif fonts
• Subtle coordinated color palette
• Print-friendly grayscale readability
• Thin professional borders

Layout Standards

• Horizontal flow for pipelines
• Clear grouping
• Consistent sizing
• Balanced whitespace

Arrow Standards (MOST CRITICAL)

• Thick strokes
• Clear arrowheads
• Dark colors
• Labeled arrows
• No crossings
• Correct direction

Color Palette (Academic Professional)

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

What to AVOID

• Rainbow color schemes
• Thin hairline arrows
• Heavy shadows or glow effects
• 3D effects
• Decorative icons that add no meaning
• Tiny unreadable text

Math Formulas in Diagrams (KaTeX)

Mermaid supports rendering mathematical expressions via KaTeX. When the diagram content involves formulas, equations, Greek letters, subscripts, superscripts, fractions, or matrices, use KaTeX notation instead of plain-text approximations.

Supported Diagram Types for Math

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

• Flowcharts — in node labels and edge labels
• Sequence Diagrams — in participant aliases, messages, and notes

Syntax Rules

• Wrap math expressions in $$ inside quoted strings:

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

• Node labels with math must be quoted
• Mix text and math by placing $$ only around the math portion
• Use \text{} for non-math text inside $$

Common Math Patterns for ML/Science Diagrams

| Concept | KaTeX Syntax |

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

| Subscript | $$W_Q$$ |

| Superscript | $$x^2$$ |

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

| Greek letters | $$\\alpha, \\beta, \\gamma$$ |

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

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

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

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

| Norm | $$\\|\\|x\\|\\|_2$$ |

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

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 or technical audiences and precision matters
• Use plain text when the diagram is for general audiences or math would add clutter
• Default to KaTeX automatically if the request already contains math notation

Gotchas

• $$ delimiters must be inside quoted strings
• Very long formulas may overflow node boxes
• Always verify rendering with mmdc

Code Quality Rules

Generated Mermaid code MUST:

• Have correct syntax that renders directly
• Have clear structure with proper indentation
• Use semantic node naming, not A, B, C
• Include styling when needed
• Use <br/> for line breaks inside node labels, never \n
• Avoid special characters that break Mermaid parsing unless properly quoted

Output Structure

figures/
├── <diagram-name>.mmd
├── <diagram-name>.md
└── <diagram-name>.png

Key Rules (MUST FOLLOW)

• Always save files to figures/
• Always generate both .mmd and .md
• Always read the relevant syntax guidance before generating code
• Always verify syntax before accepting
• Always review the rendered PNG
• Never accept score < 9
• Verify every arrow direction
• Verify every block content
• Be specific in feedback

10. Fix errors before accepting

11. Use descriptive kebab-case file names

User requirements: $ARGUMENTS