markdown-to-html

name	markdown-to-html
description	Converts a markdown file into a self-contained HTML page. Produces styled output with syntax highlighting and responsive layout. Use when the user asks to convert a markdown file or plan to HTML.
allowed-tools	Agent, AskUserQuestion, Bash(open *), Bash(realpath *), Glob, Grep, Read, TodoWrite, Write

Markdown to HTML

Convert any markdown file — plan or generic document — into a rich, self-contained HTML page that can be opened in any browser or shared via a file host.

The skill auto-detects the render mode:

• Plan mode — when the source is a plan file (has ## Steps or status: + Plan: H1)
• Doc mode — for all other markdown files

When not to use

Does not generate documentation from completed plans — use documenting-plans for that. This skill converts the source markdown into a viewable HTML file at any lifecycle stage.

Table of Contents

• Step 0 — Create progress todos
• Step 1 — Resolve the source file
• Step 2 — Parse content and detect render mode
• Step 3 — Resolve theme
• Step 4 — Check for existing output file
• Step 5 — Synthesize and write HTML
• Step 6 — Offer to open in browser
• Step 7 — Report

Instructions

Step 0 — Create progress todos

Scan $ARGUMENTS for --setup. If found, print:

--setup is deprecated. Theme CSS and JS are now bundled in the plugin.
Run the skill without --setup to generate HTML.

Then stop.

Otherwise, use TodoWrite to create todos:

• Step 1: Resolve source file
• Step 2: Parse content and detect render mode
• Step 3: Resolve theme
• Step 4: Check for existing output
• Step 5: Synthesize and write HTML
• Step 6: Offer to open in browser
• Step 7: Report

Mark each todo status: "completed" as you finish that step.

Step 1 — Resolve the source file

Path traversal defense (required before reading any file):

If a file path appears in $ARGUMENTS:

1. Run realpath "<path>" to get the canonical absolute path.
2. Confirm the result is under $PWD. If not, print "Error: path is outside the workspace" and stop.
3. Confirm the extension is .md or .markdown. If not, print "Error: file must be a .md or .markdown file" and stop.
4. Confirm realpath resolved without following a symlink outside the workspace.

If any check fails, stop with a descriptive error.

File resolution order (use first match):

1. Argument: file path in $ARGUMENTS (after passing the checks above)
2. Currently open file: .md file open in IDE that contains ## Steps, ## Context, ## Objective, ## Implementation, or ## Plan
3. Settings plansDirectory: project-local .claude/settings.local.json → project .claude/settings.json → global ~/.claude/settings.json (first that sets it) → most recently modified .md file
4. Fallback: glob ${PWD}/docs/plans/*.md, most recently modified

If no file found via any method, tell the user and stop.

Flag parsing — after resolving the file, scan $ARGUMENTS for:

• --theme=<value> — accepted: default, developer, document, minimal. Apply allow-list: if the value is not one of these four names, ignore and fall through to the Step 3 prompt. Store as pre-selected theme if valid.
• --mode=<value> — accepted: auto, plan, doc. Default: auto.
• --list-themes — if present, print the four theme names + descriptions and stop.
• --no-open — Step 6 skips the browser-open prompt.
• --background — fully non-interactive: auto-selects default theme (unless --theme also set), auto-overwrites existing output, implies --no-open.
• --async — prompts for theme in foreground, then spawns a background Agent and stops. Does not imply --background on the main thread.

Announce the resolved file: "Converting: path/to/file.md"

Step 2 — Parse content and detect render mode

Read the resolved file and extract:

• Raw H1: first line matching # … — strip only the leading # character. Keep the Plan: prefix intact at this stage; it is needed for mode detection below.
• Display title: derive from raw H1 by stripping any Plan: prefix (with or without trailing space). Use this for rendering only, not for detection.
• Frontmatter: YAML block between --- delimiters. Capture status, created, modified, type. Treat all as absent if no frontmatter.
• Sections: every ## Heading and content until the next ## Heading or EOF. Include ## Interview Summary if present.
• Steps content (if ## Steps present): parse per-step action, why, and verify text. If plain list items (no why/verify), treat as action-only steps.

Render mode detection (when --mode=auto or flag absent):

Set mode to plan when any of:

• Source contains a ## Steps section, OR
• Frontmatter has a status: key AND raw H1 starts with Plan:

Otherwise set mode to doc.

When --mode=plan or --mode=doc is passed, skip detection and use the specified mode.

Apply graceful unknown state rules from reference/html-spec.md for absent fields.

Step 3 — Resolve theme

If --list-themes was parsed, print and stop:

Available themes:
  default   — neutral grays, blue accent
  developer — dark charcoal, green accent (terminal-inspired)
  document  — warm off-white, sepia/brown accent
  minimal   — pure white, black text

If --theme=<value> was parsed and validated in Step 1, use it directly — skip prompt.

If --background was parsed and no valid --theme, use default without prompting.

Otherwise, ask via AskUserQuestion with four options:

• Default — neutral grays and white, blue accent
• Developer — dark charcoal header, green accent (terminal-inspired)
• Document — warm off-white background, sepia/brown accent
• Minimal — pure white background, black text, no accent color

Store selected theme name (lowercase, hyphenated) for Step 5.

Async dispatch (only when --async parsed AND --background NOT parsed): Now that theme is known, spawn a background agent and stop:

• subagent_type: "general-purpose"
• run_in_background: true
• description: "markdown-to-html background conversion"
• prompt: "Invoke Skill(skill: \"plan-agent:markdown-to-html\", args: \"/actual/path/to/file.md --theme=<theme> --no-open --background\") to convert the file to HTML non-interactively." — substitute real path and theme.

Output: "Background conversion started: /path/to/file.md (theme: <theme>)" and stop.

Step 4 — Check for existing output file

Derive output path: same directory as source file, same basename, .html extension.

Example: docs/plans/add-auth.md → docs/plans/add-auth.html

Use Glob to check whether the output file already exists.

If --background was parsed and file exists, overwrite automatically.

If the file exists and --background was not set, ask via AskUserQuestion:

"Output file <name>.html already exists. Overwrite?"

Options: Overwrite / Cancel. Stop if user selects Cancel.

Step 5 — Synthesize and write HTML

Read reference/html-spec.md to load the full layout contract, theme definitions, and JavaScript features. This is the authoritative source — follow it exactly.

Asset check (optimization): Attempt to Read assets/themes.css. If it succeeds, use its content verbatim as the theme block — skip re-deriving the four body.theme-* rule sets from the spec. Similarly attempt Read assets/scripts.js; if it succeeds, use it verbatim for the <script> block. If either read fails, derive from the spec as usual.

Generate a complete, self-contained HTML document. Key requirements:

Security (required — see spec "Security and Encoding" section):

• Per-sink HTML encoding for all user-controlled content
• URL allow-list for all link href values (http://, https://, mailto:, # only)
• Theme allow-list: validate before interpolating into <body class="theme-…">

Structure:

• <!DOCTYPE html> first line
• <html lang="en">, <title>, <meta charset>, <meta name="viewport">
• <a href="#main-content" class="skip-link">Skip to main content</a> as first element in <body>
• <header>, .layout grid with <nav> + <main id="main-content">
• Save as PDF button (.save-pdf-btn) in header — calls savePDF() which triggers window.print(); hidden in @media print
• Each <section> has aria-labelledby → its <h2 id>

Plan mode additions:

• Progress bar (role="progressbar", aria-valuenow/min/max, aria-label)
• Status badge
• Sidebar <div class="scroll-rail" aria-hidden="true">
• Steps as <ol class="steps-list"> with <li class="step-card"> per step
• Per-step: <label class="step-label"> wrapping checkbox + <span class="step-chip" aria-hidden="true">todo</span> + <h3 class="step-action">
• aria-describedby on each checkbox pointing to step-why-{index}
• <span class="step-status" aria-live="polite" aria-atomic="true"> live region per step
• CSS step timeline (vertical connector line + circle nodes via ::before pseudo-elements — see spec)
• SVG section diagram when ≥2 sections present (see spec "SVG Section Diagram")

Theme: Apply <body class="theme-{validated-theme}">. Use exact CSS custom property names and values from spec "Color Palette Themes".

Responsive + card styles: Include full CSS from spec "Global Styles".

Print styles: Include @media print block from spec "Print Styles".

Markdown rendering: HTML-escape first, then apply inline patterns from spec "Markdown Rendering". Apply URL allow-list to all [label](url) links. Do not markdown-render <h1>, <h2>, or fenced code block content.

JavaScript: Single <script> block immediately before </body> with:

• Scroll-spy IIFE (IntersectionObserver + aria-current="true" + scroll-rail updater)
• Step-completion IIFE with chip text update + live-region announcement (plan mode only)
• SVG node click listeners (plan mode only, when diagram present)

Write the completed HTML to the derived output path via Write.

Step 6 — Offer to open in browser

Skip entirely if --no-open or --background was set.

Ask via AskUserQuestion: "Open <name>.html in the browser?"

Options: Open / Skip.

If Open selected: run open "<output-path>" (macOS). On other platforms, inform the user browser-open is not supported and skip the open call.

Step 7 — Report

Output one line:

Written to docs/plans/add-auth.html (mode: plan, theme: developer)

Examples

/plan-agent:markdown-to-html                                                      # auto-detects from IDE or settings
/plan-agent:markdown-to-html docs/plans/add-auth.md                              # specific plan file
/plan-agent:markdown-to-html README.md --mode=doc                                # force doc mode
/plan-agent:markdown-to-html docs/plans/add-auth.md --theme=developer            # pre-select theme
/plan-agent:markdown-to-html docs/plans/add-auth.md --theme=developer --no-open  # batch-safe, no prompts
/plan-agent:markdown-to-html docs/plans/add-auth.md --background                 # fully non-interactive
/plan-agent:markdown-to-html docs/plans/add-auth.md --async --theme=developer    # background agent, no prompts
/plan-agent:markdown-to-html --list-themes                                        # print available themes and stop