Single-File HTML Composer

composing-html

Produce single-file HTML artifacts without hand-writing the page chrome. The composer supplies <!DOCTYPE>, <head>, inlined CSS, base.js, design tokens, masthead, and colophon. You supply a title and the body content.

The product is the chrome and inventory below — primitives you can drop into any artifact without re-deriving what a card, badge, or eyebrow looks like. Templates are shortcuts on top of this, useful when the same artifact shape repeats; see Templates near the end.

Default workflow: freeform

freeform gives you the whole chrome with one content slot — body_html — for the page body. Reach for it first. Reach for a template only when the structure repeats across artifacts (see Templates near the end).

There are two ways to invoke it. Use the --set flow for anything with a substantial body — it sidesteps the JSON-string escaping that bites heredoc-style spec writing (newlines, quotes, </& inside multi-line HTML).

Recommended: HTML in a file, metadata via --set

1. Write the body to a .html file directly (no JSON, no escaping).
2. python scripts/build.py build freeform \
       --set title='My Page' \
       --set subtitle='Optional subhead' \
       --set body_html=@body.html \
       --out artifact.html

--set KEY=VALUE assigns a literal string; --set KEY=@FILE loads the file contents verbatim into that spec field. Repeat for any field. Works for body_html, extra_css, extra_js, eyebrow, page_class, and the same *_html fields in any other template (summary_html, intro_html, details_html, …).

Spec-file workflow (best for structured templates)

1. python scripts/build.py describe <template>     # required keys + skeleton
2. write spec.json
3. python scripts/build.py build <template> --spec spec.json --out artifact.html

For templates with typed slots (pr_review.findings[], slide_deck.slides[], status_report.metrics[]), the spec file is the right shape — the template reasons over the structure. For freeform, the spec is mostly a thin config wrapper around one HTML string; the --set flow above is usually less friction.

You can mix both: small spec.json for metadata, --set body_html=@body.html for the heavy bit. --set overrides any matching field from --spec.

Pitfall: don't inline multi-line HTML into a JSON heredoc

cat > spec.json <<EOF { "body_html": "<multi\nline>\n..." } EOF does not produce valid JSON — JSON strings can't contain raw newlines or unescaped quotes. Either:

• use --set body_html=@body.html (recommended), or
• assemble the spec in Python with json.dump(spec, f) so escaping is automatic.

Inventory

Everything in this section is loaded into every artifact via inlined CSS and base.js. Use these tokens and classes inside body_html (or any template's *_html field) without re-declaring them.

Color tokens

Semantic aliases: --ok, --warn, --err, --info.

Type stacks

• --serif — display headings (h1, h2, big numerics).
• --sans — body text (default).
• --mono — code, eyebrows, badges, captions.

Geometry

--radius-sm (6px) · --radius (10px) · --radius-lg (16px) · --border · --border-soft · --shadow-card · --shadow-pop.

Layout primitives

• .page — main column (1080px max). Variants: .page--wide (1280px), .page--narrow (720px). Set via the page_class spec key.
• .masthead — header strip with .eyebrow + <h1> + .subtitle (auto-rendered from title/subtitle/eyebrow unless show_masthead is false).
• .grid .grid--2|3|4|auto — responsive CSS grid.
• .stack, .row — vertical / horizontal flex.
• .card, .card--soft, .card--elev — content containers.
• .rule — <hr> underline below <h2>.
• .colophon — optional footer strip; pass colophon="text" to page() to show it (off by default).

Components

• Eyebrow: <div class="eyebrow">SECTION</div> — small all-caps label with a leading clay rule.
• Badge: <span class="badge badge--ok|warn|err|info|clay">v1.0</span>.
• Kbd: <span class="kbd">⌘K</span>.
• Bullets: <ul class="bullets"><li>…</li></ul> — clay dots.
• Code: inline <code> and block <pre><code>. Block code gets a copy button automatically via base.js.
• Details: native <details><summary>…</summary>…</details> styled.

Tabs

<div class="tabgroup">
  <div class="tabs">
    <button data-target="a">Tab A</button>
    <button data-target="b">Tab B</button>
  </div>
  <div class="tab-panel" data-id="a">…</div>
  <div class="tab-panel" data-id="b">…</div>
</div>

base.js wires this automatically and selects the first tab by default.

Drag-to-reorder

<div data-sortable="true">
  <div draggable="true">…</div>
  <div draggable="true">…</div>
</div>

Optional cross-zone drops: add data-zone="<id>" to each container.

Live parameter bindings

<input type="range" data-bind="size" min="0" max="100" value="50" data-format="number" data-unit="px">
<span data-out="size"></span>
<style>.box { width: var(--bind-size, 50px); }</style>

The CSS custom property --bind-<name> is updated on every input event, and any [data-out="<name>"] element receives the formatted value.

Output rules

Spend output tokens on content, not chrome:

1. Never write <html>, <head>, <style>, <script>, or <link>. The composer adds all of them. If you find yourself writing a complete page, you missed the skill. <!-- rule:chrome-leak -->
2. Don't restate design tokens. Reuse the inventory above — var(--clay), .card, .badge--warn, .bullets, etc. are already loaded. Don't hardcode hex/rgb() colours, inline font-family/font-size, or reference tokens that aren't in the palette.

   <!-- rule:hardcoded-color rule:inline-typography rule:undefined-token -->

3. body_html is HTML, not a JSON dialect. Write <section>, <h2>, <ul class="bullets"> directly. No translation layer.
4. Anything in an _html field is inserted verbatim — escape any user-supplied content yourself. All other string values are HTML-escaped automatically.
5. One artifact per build. Browser tabs are free.