generate mermaid diagrams

Generate consistent, template-based Mermaid diagrams for technical content. Supports 12 diagram types (architecture, flowchart, sequence, concept-map, radial-concept, timeline, comparison, comparison-table, gantt, mindmap, class-diagram, state-diagram) with automatic template selection, LLM-powered content generation, syntax validation, and error handling. Use when creating technical illustrations, system architecture visuals, project timelines, class diagrams, state machines, or documentation requiring uniform styling. Triggers on "mermaid diagram", "generate diagram", "create flowchart", "architecture diagram", "sequence diagram", "concept map", "gantt chart", "mind map", "class diagram", "UML diagram", "project timeline", "state diagram", "technical illustration".

Mermaid Diagrams

Generate professional, consistently-styled Mermaid diagrams for technical content with automatic template selection, content generation, and quality validation.

Quick Start

Subagent Pattern (Recommended):

When user requests diagram generation, spawn a subagent:

text

Generate 3 Mermaid diagrams for /path/to/chapter-01.md and save to diagrams/chapter-01/

The subagent will:

1. Read chapter content
2. Select appropriate templates
3. Generate placeholder content
4. Create content.json
5. Run generation script
6. Validate output

Manual Pattern:

bash

# 1. Create content.json (see assets/example-content.json)
# 2. Render diagrams
node scripts/generate.mjs --content content.json --out diagrams/chapter-01

# 3. Validate
node scripts/validate.mjs --dir diagrams/chapter-01

Prerequisites

Automated Installation (Recommended)

Run the installation script to automatically install and verify mermaid-cli:

bash

cd $SKILL_DIR  # Path to skill-mermaid-diagrams directory
./scripts/install-deps.sh

The script will:

• Check Node.js version (>= 18.0.0 required)
• Install or upgrade mermaid-cli to latest version
• Verify installation and version compatibility
• Provide troubleshooting guidance if needed

Manual Installation

Alternatively, install Mermaid CLI globally:

bash

npm install -g @mermaid-js/mermaid-cli

Verify installation:

bash

mmdc --version  # Should be >= 11.0.0

Usage Patterns

Subagent Workflow (Primary Pattern)

When a user requests diagram generation, spawn a subagent to handle the complete workflow:

text

Task: Generate 3 Mermaid diagrams for chapter 5

Steps:
1. Read $CONTENT_DIR/chapters/chapter-05.md
2. Analyze content and select 3 appropriate diagram templates from: architecture, flowchart, sequence, concept-map, timeline, comparison
3. For each selected template:
   - Read template from $SKILL_DIR/assets/
   - Extract placeholders ({{PLACEHOLDER_NAME}} format)
   - Generate concise labels (max 8 words each) based on chapter content
4. Create content.json with structure:
   {
     "chapter": "chapter-05.md",
     "diagrams": [
       {
         "template": "architecture",
         "placeholders": { "SYSTEM_NAME": "...", ... }
       },
       ...
     ]
   }
5. Save to $CONTENT_DIR/diagrams/chapter-05/content.json
6. Run: node $SKILL_DIR/scripts/generate.mjs --content content.json --out $CONTENT_DIR/diagrams/chapter-05
7. Validate: node $SKILL_DIR/scripts/validate.mjs --dir $CONTENT_DIR/diagrams/chapter-05
8. Report success with file count

Note: Replace $SKILL_DIR and $CONTENT_DIR with actual paths:
- SKILL_DIR: Path to skill-mermaid-diagrams directory
- CONTENT_DIR: Path to your content/project directory

Manual Content Generation

If generating content.json manually:

bash

# 1. Create content.json (see assets/example-content.json)
# 2. Render
cd $SKILL_DIR  # Path to skill-mermaid-diagrams directory
node scripts/generate.mjs \
  --content /path/to/content.json \
  --out /path/to/output

# 3. Validate
node scripts/validate.mjs --dir /path/to/output

Parameters:

• --content / -c: Content JSON file (required)
• --out / -o: Output directory (default: ./diagrams)

Validate All Generated Diagrams

bash

for dir in diagrams/chapter-*/; do
  node scripts/validate.mjs --dir "$dir"
done

Available Templates

The skill includes 12 professionally-themed templates with consistent color schemes:

1. architecture.mmd - System architecture, component diagrams, tool integration

   • Use for: System components, tool pipelines, agent interactions
   • Fixed node IDs (space-safe): Uses C1, C2, C3 internally, only labels are customizable

2. flowchart.mmd - Decision flows, processes, workflows, debugging steps

   • Use for: Decision trees, process flows, validation workflows

3. sequence.mmd - Actor interactions, message passing, session patterns

   • Use for: API call sequences, actor communication, message flows

4. concept-map.mmd - Key concepts, mental models, paradigms, relationships

   • Use for: Hierarchical concepts, mental models, knowledge graphs
   • Improved version (graph-based, not mindmap): Full color control, readable text

5. radial-concept.mmd - Layered concepts radiating from center - Use for: Progressive summarization, abstraction layers, hierarchical models

   • 4 color-coded levels: green → orange → blue → purple

6. timeline.mmd - Temporal progression, optimization stages, evolution

   • Use for: Project phases, evolution timelines, staged processes

7. comparison.mmd - Trade-offs, quadrant analysis (2D plotting)

   • Use for: Cost vs performance, effort vs impact (X/Y coordinate plotting)
   • Requires X/Y coordinates for items

8. comparison-table.mmd - Side-by-side feature comparison

   • Use for: AI vs Script decisions, option comparisons, feature matrices
   • Alternative to quadrant when you need simple side-by-side, not 2D plotting

9. gantt.mmd - Project timelines, task scheduling - Use for: Project planning, milestone tracking, task dependencies

   • Supports: Multiple sections, task status (done/active/crit), date ranges

10. mindmap.mmd - Organic radial mind maps - Use for: Brainstorming, organic thought structures, free-form concept mapping

    • Limitation: Auto-assigns colors/text (limited theme control)
    • Alternative: Use radial-concept.mmd for better color control

11. class-diagram.mmd - UML class diagrams

    • Use for: Object models, database schemas, system architecture (OOP)
    • Supports: Attributes, methods, relationships (inheritance, composition, association)

12. state-diagram.mmd - State machines, lifecycle diagrams

    • Use for: Process states, object lifecycles, workflow stages
    • Supports: Transitions with labels, notes on states, start/end markers

Template Placeholder Reference

Each template requires specific placeholders. All placeholders must be provided to avoid rendering errors.

Template	Placeholders	Complexity	Required Fields
architecture	10	Medium	SYSTEM_NAME, COMPONENT_1-3_LABEL, EXTERNAL_1-2_LABEL, FLOW_1-4
flowchart	11	Medium	START_LABEL, DECISION_1-2, ACTION_1-4, CHOICE_1-2_YES/NO, END_LABEL
sequence	8	Medium	ACTOR_1-3, MESSAGE_1-5
concept-map	15	High	CENTRAL_CONCEPT, BRANCH_1-4, BRANCH_X_SUB_1-3
radial-concept	13	Medium	CENTRAL_CONCEPT, LEVEL_1-4_LABEL, LEVEL_X_NODE_1-3
timeline	6	Low	EVENT_1-6, DATE_1-6
comparison	18	High	COMPARISON_TITLE, X/Y_AXIS_LOW/HIGH, QUADRANT_1-4_LABEL, ITEM_1-5 + X/Y coords
comparison-table	10	Low	OPTION_1-2_TITLE, OPTION_X_CRITERION_1-4
gantt	14	High	CHART_TITLE, SECTION_1-3_TITLE, TASK_X_Y (name/id/start/duration)
mindmap	13	Medium	ROOT_CONCEPT, BRANCH_1-4, BRANCH_X_CHILD_1-3
class-diagram	21	High	CLASS_1-3_NAME, CLASS_X_ATTR_1-3, CLASS_X_METHOD_1-3, REL_1-3_TYPE/LABEL
state-diagram	18	Medium	STATE_1-8, TRANSITION_1-7_LABEL, STATE_1/4/7_NOTE

Important Notes:

• architecture.mmd: Uses fixed node IDs (C1, C2, C3, E1, E2) internally. Only *_LABEL placeholders are customizable. Labels can contain spaces (space-safe).
• concept-map.mmd: Improved graph-based version (replaced mindmap). Better color control and readability.
• comparison.mmd: QuadrantChart requires X/Y coordinates. Use comparison-table.mmd for simple side-by-side comparisons.
• gantt.mmd: Task status options: done, active, crit, or blank. Date format: YYYY-MM-DD. Duration: Nd (days) or YYYY-MM-DD.
• mindmap.mmd: Limited theme control (auto-colors, auto-text). For controlled colors/text, use radial-concept.mmd instead.
• class-diagram.mmd: Relationship types: <|-- (inheritance), *-- (composition), o-- (aggregation), --> (association), ..> (dependency).
• state-diagram.mmd: Uses stateDiagram-v2 syntax. States are simple identifiers (no spaces). Notes attach to states 1, 4, and 7.
• Text length limits: Generator warns if labels exceed recommended length (25-50 chars depending on template).

Placeholder Naming Convention:

• Component labels: COMPONENT_1_LABEL, COMPONENT_2_LABEL
• Branch hierarchy: BRANCH_1, BRANCH_1_SUB_1, BRANCH_1_SUB_2
• Level-based: LEVEL_1_LABEL, LEVEL_1_NODE_1

---

Changelog & Migration Notes

v2.0 (2026-02-15) - Root Cause Fixes

Breaking Changes:

1. architecture.mmd - Fixed node ID handling (space-safe)

   • Before: Used placeholder values as node IDs → failed when labels contained spaces
   • After: Uses fixed node IDs (C1, C2, C3) → labels can contain any characters
   • Migration: Remove COMPONENT_1, COMPONENT_2, COMPONENT_3 from content.json (only *_LABEL variants needed)

2. concept-map.mmd - Replaced mindmap with graph-based version

   • Before: Mindmap syntax with auto-colors, black-on-purple text (unreadable)
   • After: Graph LR syntax with explicit styling, white text on dark backgrounds
   • Result: +100% contrast improvement (2.6:1 → 5.2:1 on purple nodes) New Features:

• radial-concept.mmd - Progressive summarization diagrams with 4 color-coded levels
• comparison-table.mmd - Side-by-side feature comparison (alternative to quadrant chart)
• Validation - Generator now warns about text length, unresolved placeholders, special characters

All changes target root causes (template design flaws, missing validation) rather than surface symptoms.

---

Color Scheme (Consistent Across All Templates)

• Primary Blue: #4A90E2 - Main components, actions
• Secondary Purple: #7B68EE - Supporting elements
• Tertiary Green: #90EE90 - External actors, success states
• Warning Yellow: #FFD700 - Decisions, cautions
• Error Red: #FF6B6B - Failures, critical paths

Output Structure

After generation, each chapter directory contains:

text

diagrams/chapter-01/
├── diagram-01-architecture.mmd   # Mermaid source
├── diagram-01-architecture.svg   # Vector output
├── diagram-01-architecture.png   # Raster output (1200px wide)
├── diagram-02-flowchart.mmd
├── diagram-02-flowchart.svg
├── diagram-02-flowchart.png
├── diagram-03-concept-map.mmd
├── diagram-03-concept-map.svg
├── diagram-03-concept-map.png
└── summary.json                   # Generation metadata

Error Handling

The generator includes robust error handling:

• Template Selection Failure: Falls back to first N templates in order
• Content Generation Failure: Skips diagram, continues with next
• Rendering Failure: Reports error, saves .mmd source for manual debugging
• Missing mmdc CLI: Exits early with installation instructions

Quality Validation

The validator checks each diagram for:

1. ✅ File readable and valid UTF-8
2. ✅ Theme configuration present
3. ✅ No unresolved placeholders ({{PLACEHOLDER}})
4. ✅ SVG file rendered
5. ✅ PNG file rendered
6. ✅ Syntax valid (can re-render without errors)

Validation workflow:

bash

# Generate diagrams
node scripts/generate.mjs --content content.json --out diagrams/chapter-01

# Validate output
node scripts/validate.mjs --dir diagrams/chapter-01

# Fix any failures and re-run

Cost Analysis

Per Chapter (3 diagrams):

• Subagent LLM usage:
  • Chapter reading: ~3000 tokens input
  • Template selection: ~500 tokens output
  • Content generation (3 diagrams): ~1500 tokens output
  • Total: 5000 tokens ($0.002)
• Rendering: Free (local mmdc)

At scale (e.g. 14 chapters × 3 diagrams = 42 diagrams):

• 14 × $0.002 = ~$0.03 total

Comparison to AI image generation (42 images):

• Mermaid diagrams: ~$0.03
• GLM images: ~$0.63
• DALL-E images: ~$2.52
• Savings: 95-99% vs AI image generation

Customization

Modify Color Scheme

Edit theme variables in any template file (assets/*.mmd):

Rendering diagram...

Add New Template

1. Create assets/new-template.mmd with theme and placeholders
2. Add entry to TEMPLATES object in scripts/generate.mjs:

javascript

const TEMPLATES = {
  ...
  "new-template": "Description of when to use this template",
};

3. Test with content:

bash

node scripts/generate.mjs --content test-content.json --out test-output

Troubleshooting

"mmdc not found"

• Install: npm install -g @mermaid-js/mermaid-cli
• Verify: which mmdc

"Template not found"

• Check template name in content.json matches file in assets/ (case-sensitive)
• Available templates: architecture, flowchart, sequence, concept-map, radial-concept, timeline, comparison, comparison-table, gantt, mindmap, class-diagram, state-diagram

"Rendering failed"

• Check .mmd file for syntax errors
• Manually test: mmdc -i diagram.mmd -o test.svg
• Validate with: node scripts/validate.mjs --dir output_dir

Unresolved placeholders in output ({{PLACEHOLDER}})

• Subagent didn't generate all required placeholder values
• Check template file to see required placeholders
• Manually add missing values to content.json and re-run generate.mjs

Subagent failed

• Check chapter file path is correct
• Verify skill path is accessible from subagent
• Ensure mmdc is installed globally (subagent needs it too)

Examples

Generated Architecture Diagram

Rendering diagram...

Output: Clean, consistent, professional diagram with uniform styling across all chapters.

Best Practices

1. Consistent counts: Use same --max value for all chapters (e.g., 3)
2. Review before commit: Run validator on all outputs before pushing
3. Version control: Commit both .mmd source and .svg/.png renders
4. Iterate templates: If diagrams look wrong, adjust template then regenerate
5. Manual touch-ups: Edit .mmd files directly for fine-tuning, then re-render with mmdc

Testing

Installation Test

bash

./scripts/install-deps.sh

Verifies that mermaid-cli is installed and meets version requirements.

Functional Test

1. Create test content: assets/example-content.json (already included)
2. Generate diagrams: node scripts/generate.mjs --content assets/example-content.json --out test-output
3. Validate output: node scripts/validate.mjs --dir test-output
4. Verify all checks pass

References

Local Documentation

• Mermaid Syntax Guide: references/mermaid-syntax.md - Quick reference for diagram syntax, theming, and common patterns
• Example Content: assets/example-content.json - Real-world content structure example

External Resources

• Mermaid Docs: https://mermaid.js.org/
• Syntax Reference: https://mermaid.js.org/intro/syntax-reference.html
• Theming Guide: https://mermaid.js.org/config/theming.html
• CLI Documentation: https://github.com/mermaid-js/mermaid-cli
• Live Editor: https://mermaid.live/ (interactive testing)