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

1. Analyze user description to determine the most suitable diagram type
2. Read the corresponding syntax reference documentation (see Diagram Type Reference below)
3. 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
4. Identify all components, connections, and data flow
5. 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:

1. Read the error message carefully
2. Fix the syntax issue in both .mmd and .md files
3. Re-run verification
4. 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 servi