Web Prototype Skill

Produce a single, self-contained HTML prototype using the bundled seed and layout library — not by writing CSS from scratch. The seed already encodes good defaults (typography, spacing, accent budget). Your job is to compose it.

Resource map

web-prototype/
├── SKILL.md                ← you're reading this
├── assets/
│   └── template.html       ← seed: tokens + class system + chrome (READ FIRST)
└── references/
    ├── layouts.md          ← 8 paste-ready section skeletons
    └── checklist.md        ← P0/P1/P2 self-review

Workflow

Step 0 — Pre-flight (do this once before writing anything)

1. Read assets/template.html end-to-end — at minimum through the <style> block. The class inventory at the top of references/layouts.md lists every class that must be defined there; if one is missing, add it to <style> rather than re-defining it inline on every section.
2. Read references/layouts.md so you know which section skeletons exist. Don't write a section type that isn't covered — pick the closest layout and adapt.
3. Read the active DESIGN.md (already injected into your system prompt). Map its colors to the six :root variables in the seed; don't introduce new tokens.

Step 1 — Prepare index.html from the seed

Use assets/template.html as the seed for the canonical project file, normally index.html.

Replace the six :root variables with the active design system's tokens. Replace the page <title> and the topnav brand.

Step 2 — Plan the section list

Pick layouts before writing copy. Default rhythms (from layouts.md):

State the chosen list in one sentence to the user before writing — they can redirect cheaply now and not after 200 lines of HTML.

Step 3 — Paste and fill

For each chosen layout, copy the <section> block from layouts.md into <main id="content"> of the project HTML. Replace bracketed [REPLACE] strings with real, specific copy from the user's brief. No filler — if a slot is empty, the section is the wrong choice; pick a different layout. Treat every .ph-img block as layout scaffolding and replace it when the section requires imagery, following the real-first rule below before self-checking.

Step 4 — Self-check

Run through references/checklist.md top to bottom. Every P0 item must pass before you move on. P1 items should pass; P2 are bonus.

Step 5 — Write the project file

Write the completed HTML to the canonical project file, normally index.html. Then send one short ordinary assistant summary naming the file and describing what's there. Do not output the full HTML source in chat.

Hard rules (the seed protects most of these — don't fight it)

• Single accent, used at most twice per screen. Eyebrow + primary CTA is the default budget.
• Display font is serif (Iowan Old Style / Charter / Georgia in the seed). Sans for body. Mono for numerics, captions, eyebrows.
• Real imagery, never remote hotlinks. .ph-img is temporary layout scaffolding, not the default final treatment. For a named real-world referent, search/fetch the correct real image, copy it into the project, and reference it relatively; never generate, draw, or invent a substitute. For illustrative or atmospheric subjects, prefer suitable fetched real photography and use image generation only as a fallback. If no compliant asset can be acquired, keep an intentional labeled .ph-img and disclose the limitation in the delivery summary.
• Preserve real-image geometry. Inspect each acquired image's intrinsic width and height, replace the entire .ph-img scaffold with an <img class="content-img">, and set matching width and height attributes. Never copy .ph-img, .wide, .portrait, or .square onto a real image. Content images must show the full frame; object-fit: cover is only for intentionally croppable decorative fills. The seed's .content-img rule bounds unusually tall or wide images to the viewport while keeping the other axis automatic.
• Mobile reflow already works via the seed's media query at 920px. Don't break it by adding fixed widths.
• data-od-id on every <section> so comment mode can target it.

Output contract

Filesystem runs use project files as the source of truth:

index.html

OpenDesign derives the preview from the written project file. Do not also emit a source-code <artifact> block for the same generation turn.

One short summary after writing the file. Nothing after.