md-to-html

Markdown to HTML Conversion

Write in Markdown, share as a polished web page — zero dependencies for viewers

Convert Markdown documents into self-contained HTML files with embedded CSS, base64 images, and Mermaid diagram rendering. Ready for quick-share distribution, offline viewing, print, or email attachment.

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When to Use

• Sharing formatted documents without requiring Word or PDF viewers
• Creating self-contained HTML pages for offline distribution
• Generating printable web pages from Markdown sources
• Quick previews of documentation with professional styling
• Email attachments that open in any browser
• Static site generation from Markdown sources

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Supported Formatting

Format	Status	Notes
Headings	✅	H1-H6 with styled colors
Bold/Italic	✅	Standard emphasis
Links	✅	Styled with underline on hover
Images	✅	Base64 embedded or linked
Code blocks	✅	Syntax highlighting, monospace font
Inline code	✅	Background highlight
Tables	✅	Striped rows, header styling
Blockquotes	✅	Left border, italic style
Lists	✅	Ordered, unordered, nested
Task lists	✅	Checkbox rendering
Mermaid diagrams	✅	PNG or table fallback
SVG	✅	Inline or base64 embedded
Horizontal rules	✅	Styled dividers
Footnotes	✅	Via pandoc
Math (KaTeX)	⚠️	Requires --katex flag

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Key Features

Feature	Details
Style presets	professional, academic, minimal, dark
Self-contained	All CSS embedded in <style> block, no external deps
Image embedding	Local images converted to base64 data URIs
Mermaid support	PNG rendering or table fallback for diagrams
Print-ready	CSS @media print rules included
TOC generation	Optional table of contents via --toc
Frontmatter	Extracted for title, stripped from output

Usage

# Basic conversion (professional style)
node .github/muscles/md-to-html.cjs report.md

# Academic style with TOC
node .github/muscles/md-to-html.cjs thesis.md --style academic --toc

# Dark mode output
node .github/muscles/md-to-html.cjs docs.md --style dark

# Mermaid diagrams rendered as PNG (high quality)
node .github/muscles/md-to-html.cjs architecture.md --mermaid-png

# Custom output path
node .github/muscles/md-to-html.cjs README.md output/readme.html

# Dry run (validate without generating)
node .github/muscles/md-to-html.cjs report.md --dry-run

# Debug mode (save preprocessed markdown)
node .github/muscles/md-to-html.cjs report.md --debug

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Options Reference

Option	Default	Description
--style PRESET	professional	Style preset: professional, academic, minimal, dark
--toc	off	Generate table of contents from headings
--embed-images	true	Convert local images to base64 data URIs
--no-embed-images	-	Keep image paths as-is (external references)
--strip-frontmatter	true	Remove YAML frontmatter from output
--mermaid-png	off	Render Mermaid as PNG (requires mmdc)
--mermaid-fallback	default	Convert Mermaid to table representation
--debug	off	Save preprocessed markdown as _debug_combined.md
--dry-run	off	Validate only, no HTML output

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Style Presets

Preset	Font	Max Width	Colors	Best For
professional	Segoe UI	900px	Blue headings, white bg	Business docs, reports
academic	Palatino Linotype	750px	Dark headings, cream bg	Papers, theses
minimal	Inter	800px	Black/gray, white bg	Clean, modern pages
dark	Segoe UI	900px	Light text, dark bg	Dark mode preference

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Mermaid Diagram Support

Diagram Type	PNG Mode	Fallback Mode
Flowchart	✅ Full render	✅ Table
Sequence	✅ Full render	✅ Table
Class	✅ Full render	✅ Table
State	✅ Full render	✅ Table
ER	✅ Full render	✅ Table
Gantt	✅ Full render	⚠️ Limited
Pie	✅ Full render	✅ Table
Journey	✅ Full render	⚠️ Limited

PNG Mode (--mermaid-png): Requires mermaid-cli (mmdc). Renders at scale 8, 2400px width for crisp output. Diagrams are embedded as base64 PNGs.

Fallback Mode (default): No external dependencies. Converts diagram syntax to an ASCII table representation suitable for text-only viewing.

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Print Styling

HTML output includes @media print CSS rules:

• Page breaks before H1 headings
• No background colors (ink-friendly)
• Link URLs shown after text
• Code blocks with borders instead of background
• Proper margins for binding

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Batch Processing

# Convert all markdown files in a directory
for file in docs/*.md; do
  node .github/muscles/md-to-html.cjs "$file" --style professional
done

# PowerShell equivalent
Get-ChildItem docs/*.md | ForEach-Object {
  node .github/muscles/md-to-html.cjs $_.FullName --style professional
}

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Troubleshooting

Problem	Cause	Solution
"pandoc not found"	pandoc not installed	winget install pandoc
Mermaid not rendering	mmdc not installed	npm install -g @mermaid-js/mermaid-cli or use fallback
Images missing	Relative paths broken	Use --embed-images (default)
Output too wide on print	Style preset issue	Use academic style for print
Special characters garbled	Encoding issue	Ensure source is UTF-8

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Requirements

• Node.js 18+
• pandoc (winget install pandoc)
• mermaid-cli (optional, only for --mermaid-png)

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Muscle Script

.github/muscles/md-to-html.cjs (v1.0.0)

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Conversion Acceptance Decision Table

Condition	Verdict	Action
All headings, lists, tables, code blocks render correctly	Accept	Ship as-is
Mermaid diagrams rendered as PNG/SVG with correct layout	Accept	Verify diagram labels readable
Mermaid diagrams missing or show raw syntax	Reject	Check mermaid-cli installed; re-run with --mermaid-png
Math equations (KaTeX/MathJax) render correctly	Accept	Spot-check complex equations
Math equations show raw LaTeX source	Reject	Verify KaTeX CSS/JS included in template
Embedded images display at correct size	Accept	Confirm no broken <img> tags
Images missing or show broken placeholders	Reject	Check paths are relative and files exist
CSS custom properties resolve (colors, fonts)	Accept	Visual spot-check against brand
Inline styles lost or overridden by browser defaults	Warning	Add !important or inline fallbacks
Output file size >5MB for a simple document	Warning	Check for unoptimized base64 images
HTML validates (no unclosed tags, no script injection)	Accept	Required for security
HTML contains <script> from untrusted source	Reject	Sanitize; only allow known libraries

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Related Skills

• md-to-word — Sister converter for Word document output
• md-scaffold — Generate converter-ready Markdown templates
• markdown-mermaid — Diagram authoring for embedded Mermaid
• lint-clean-markdown — Pre-validate markdown before conversion
• nav-inject — Add navigation tables for multi-file suites

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Skill version: 2.0.0 | Last updated: 2026-04-14 | Category: document-conversion

Falsifiability

• This skill is wrong if generated HTML fails W3C validation on structural elements the skill explicitly handles
• The conversion flags are stale if Pandoc changes default HTML5 output behavior in a major version
• Not earning tokens if the output loses semantic structure (headings, lists, code blocks) that raw Pandoc preserves without the documented options