diagram-generator

Diagram Generator — creates Mermaid diagrams and standalone HTML exports for architecture, schemas, flows, and all supported diagram types.

Diagram Types

Type	Keyword	Best For
Flowchart	flowchart TB/LR	Decision flows, processes
Sequence	sequenceDiagram	API interactions, protocols
Class	classDiagram	OOP structure, interfaces
State	stateDiagram-v2	Lifecycle, state machines
ER	erDiagram	Database schemas
Gantt	gantt	Project timelines
Pie	pie	Distribution, composition
Mindmap	mindmap	Hierarchical mind maps
Timeline	timeline	Chronological events
Git Graph	gitGraph	Branch visualization
Kanban	kanban	Task boards
Quadrant	quadrantChart	2x2 matrix

Processing Limits

• File chunk limit: 1000 files per diagram (HARD LIMIT)
• Visual limit: ~200 nodes max per diagram
• Large codebases: split by subsystem/layer; generate overview first then details

Standalone HTML Output Mode

Trigger phrases: "export as HTML", "standalone diagram", "interactive diagram"

Generate a self-contained HTML file with embedded Mermaid.js CDN, dark/light toggle button, and responsive CSS (max-width: 1200px):

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>TITLE</title>
    <script src="https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.min.js"></script>
    <script>
      mermaid.initialize({ startOnLoad: true, theme: 'dark' });
    </script>
    <style>
      body {
        font-family: system-ui;
        max-width: 1200px;
        margin: 2rem auto;
        background: #1e1e2e;
        color: #cdd6f4;
      }
    </style>
  </head>
  <body>
    <h1>TITLE</h1>
    <button
      onclick="let d=!d;mermaid.initialize({startOnLoad:false,theme:d?'dark':'default'});document.querySelector('.mermaid').removeAttribute('data-processed');mermaid.run()"
    >
      Toggle Theme
    </button>
    <div class="mermaid">MERMAID_CONTENT</div>
  </body>
</html>

Default: dark mode (background: #1e1e2e, color: #cdd6f4) Output: .claude/context/artifacts/diagrams/{subject}-{YYYY-MM-DD}.html

Output Location

• Mermaid files: .claude/context/artifacts/diagrams/{subject}-{type}-{YYYY-MM-DD}.mmd
• HTML files: .claude/context/artifacts/diagrams/{subject}-{YYYY-MM-DD}.html

Iron Laws

1. Mermaid syntax only — no ASCII art or PlantUML.
2. Never exceed 200 nodes per diagram.
3. Never write diagrams outside .claude/context/artifacts/diagrams/.
4. Label all non-obvious connections.
5. Enforce 1000-file hard limit — chunk large codebases.

Mermaid Plugin Generation Pattern

Generate diagrams from code analysis using the Claude Code plugin pattern (ref: agentic-coding-school/mermaid-diagram-plugin):

Step 1: Analyze Codebase Structure

# Identify components to diagram
pnpm search:code "class|interface|module|service|component" | head -50

Step 2: Generate Mermaid Source

Use Claude to transform code analysis into diagram syntax. Always request a specific diagram type and scope:

"Generate a Mermaid flowchart TB of the authentication flow in src/auth/"
"Create an ER diagram for the database tables in prisma/schema.prisma"
"Make a sequence diagram for the API request lifecycle in src/api/"

Step 3: Render Interactive HTML

For standalone shareable diagrams, use the full HTML template:

// Plugin invocation pattern (from mermaid-diagram-plugin)
const mermaidContent = `
flowchart TB
  A[User Request] --> B{Auth Check}
  B -- Valid --> C[Route Handler]
  B -- Invalid --> D[401 Response]
  C --> E[Database Query]
  E --> F[Response]
`;

// Render to interactive HTML
const html = `<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>${title}</title>
    <script src="https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.min.js"></script>
    <script>mermaid.initialize({ startOnLoad: true, theme: 'dark' });</script>
    <style>
      body { font-family: system-ui; max-width: 1200px; margin: 2rem auto;
             background: #1e1e2e; color: #cdd6f4; }
      .controls { margin-bottom: 1rem; }
      button { padding: 0.5rem 1rem; margin-right: 0.5rem; cursor: pointer; }
    </style>
  </head>
  <body>
    <h1>${title}</h1>
    <div class="controls">
      <button onclick="toggleTheme()">Toggle Theme</button>
      <button onclick="downloadSVG()">Download SVG</button>
    </div>
    <div class="mermaid">${mermaidContent}</div>
    <script>
      let dark = true;
      function toggleTheme() {
        dark = !dark;
        mermaid.initialize({ startOnLoad: false, theme: dark ? 'dark' : 'default' });
        document.querySelector('.mermaid').removeAttribute('data-processed');
        mermaid.run();
      }
      function downloadSVG() {
        const svg = document.querySelector('.mermaid svg');
        if (!svg) return;
        const blob = new Blob([svg.outerHTML], { type: 'image/svg+xml' });
        const a = document.createElement('a'); a.href = URL.createObjectURL(blob);
        a.download = '${title.replace(/\s+/g, '-')}.svg'; a.click();
      }
    </script>
  </body>
</html>`;

Step 4: Save Output

# Save interactive HTML to standard location
# .claude/context/artifacts/diagrams/{subject}-{YYYY-MM-DD}.html

Plugin Invocation from Agent

When an agent needs a diagram as part of a workflow:

// Invoke diagram-generator skill, then request specific type
Skill({ skill: 'diagram-generator' });

// Then describe what to diagram with context
// "Create a class diagram for src/lib/routing/ — show all classes and their relationships"

When to invoke

Skill({ skill: 'diagram-generator' }) for architecture diagrams, HTML exports, mindmaps, timelines, git visualizations, kanban boards, and quadrant charts.