Frontend Design

Frontend Design

Purpose

Stage: Spec (UI only). This is the ONE skill that owns the UI. It does two things with a single thesis: it explores throwaway variants to answer "what should this look like," then commits ONE high-fidelity prototype = the reference-spec build target production re-implements — and writes the design contract that records the aesthetic decisions in durable form. The same design thesis that authors the prototype here supplies the grading rubric quality-verification uses in Verify: one mind writes the UI and checks the UI. Approach this as the design lead at a small studio known for giving every client a visual identity that could not be mistaken for anyone else's — make deliberate, opinionated choices about palette, typography, and layout specific to this brief, and take one real aesthetic risk you can justify.

When to use / when to skip

• Use when prd.md describes a feature with a UI surface (a page, screen, component, or flow) and

the look is not already fully pinned. This runs in Spec, after to-prd, before acceptance-criteria/environment-manifest sign-off.

• Skip when the feature has no UI (a pure API, a CLI, a data pipeline) — then there is no design

contract and quality-verification runs no design gate. Skip the exploration phase (go straight to commit) when the brief already pins the visual direction exactly — the brief's own words always win, including when it asks for a look you'd otherwise call a default.

• depth: lite — a tiny, low-stakes surface (one isolated component, an internal tool) may collapse to a

single committed prototype + a 3-line contract; say so at the top and keep the rubric axes, just terse.

Inputs

• prd.md (from to-prd) — read Solution and User Stories for what the surface must do and for whom;

read Out of Scope for what NOT to design. Refuse to run if prd.md is absent (nothing to design against). prd.md carries no file paths or signatures by contract, so design freely.

• intent.md (optional, from interview-me) — Outcome · User · Why ground the subject. If memory holds

the human's preferences or prior designs, use them as a hint.

• If prd.md describes no UI surface, emit nothing and hand back "no UI — skip frontend-design."

Process: explore throwaway variants → commit ONE prototype + write the contract

Phase 0 — Ground it in the subject

If the brief doesn't pin down what the product/subject is, pin it yourself: name one concrete subject, its audience, and the page's single job, and state your choice. The subject's own world — its materials, instruments, artifacts, vernacular — is where distinctive choices come from. Build with the brief's real content throughout.

Phase 1 — Explore with the visual companion (default)

When "what should this look like" is genuinely open, explore with the visual companion — the default mechanism. Start it with scripts/start-server.sh --project-dir . --open; it prints a server-started JSON line with a keyed url. Write several structurally-different mockup screens into its content dir, and the human's browser auto-opens to the first one (it then shows the newest screen each time you write one). When auto-open isn't possible — headless or remote — share the printed URL so the human opens it manually; the companion works identically either way. It works greenfield, before any app or framework exists (no running app needed). Default to 3 variants; cap at 5 (more stops being radically different). Variants must be structurally different — different layout, information hierarchy, primary affordance — not three recolored card grids.

Offer the companion just-in-time and per-question: a visual layout/look question goes to the browser; a textual clarifying question (scope, terminology, a tradeoff) stays in the terminal — don't push the human into the browser for words. The interesting feedback is usually "the header from B with the sidebar from C" — that's the actual design; do most of this iteration in your own thinking and only surface ideas you have high confidence will delight. Exploration is scratch you discard — throwaway screens stay in the gitignored .frontend-design/ working dir; only the agreed mockup survives (committed in Phase 3). See references/visual-companion.md for the operating detail (start / loop / read-events / stop).

When the target app already exists and the design judgment depends on real in-app data and density, escalate to the in-app ?variant= switcher (see references/exploring-variants.md) so variants butt up against the real header/sidebar/data rather than looking fine in a vacuum.

Phase 2 — Plan the design (two-pass)

First, brainstorm a compact token system for the chosen direction:

• Color — the palette as 4–6 named hex values.
• Type — typefaces for 2+ roles (a characterful display face used with restraint, a complementary body

face, a utility face for captions/data if needed); a clear type scale with intentional weights, widths, spacing.

• Layout — a layout concept in one-sentence prose + ASCII wireframes to compare.
• Signature — the single unique element this page will be remembered by, embodying the brief.

Then review the plan against the brief before building: if any part reads like the generic default you'd produce for any similar page (work through a similar prompt to see if you land somewhere similar) rather than a choice made for THIS brief — revise it, and say what you changed and why. Only after confirming relative uniqueness do you write code, deriving every color and type decision from the revised plan.

Phase 3 — Commit ONE high-fidelity prototype (the reference-spec mockup)

Build the chosen direction to a real quality floor — this committed prototype is the reference-spec build target that production re-implements: the design source-of-truth Verify grades fidelity against, not a throwaway, and not shipped code itself (production re-implements it in the target's real stack — the degenerate exception is a target that genuinely is static HTML). It is the single mockup the human agreed on in the visual companion (Phase 1), now promoted to the committed docs/features//prototype/index.html; the companion's throwaway screens are discarded, this one mockup survives. When writing CSS, watch selector specificity: type-based (.section) vs element-based (.cta) selectors easily cancel each other out, especially section paddings/margins. Critique your own work as you build — take screenshots if your environment supports it (a picture is worth 1000 tokens). Apply Chanel's rule: before you ship it, remove one accessory.

Phase 4 — Write the design contract

Record the locked decisions as the design contract (see the sections below), status: draft — the seven rubric axes plus the ## Prototype section that names the committed reference-spec mockup and its fidelity bar. This is the ONLY home for design floors/rubric/fidelity — none of it goes into acceptance.md. The human signs it at the Spec gate (status: signed).

Design rubric (= the design contract's seven rubric sections AND the Verify grading axes)

These seven axes are written here in Spec and re-read by quality-verification in Verify: quality-verification grades the built UI against (i) fidelity to this committed prototype and (ii) these axes. Fill every one in the contract.

1. Distinctiveness / not-an-AI-default. The hero is a thesis: open with the most characteristic thing in

the subject's world (headline, image, animation, live demo, interactive moment). Calibration: AI-generated design right now clusters around three looks — (a) warm cream background (~#F4F1EA) + high-contrast serif display + terracotta accent; (b) near-black background + one bright acid-green/vermilion accent; (c) broadsheet layout with hairline rules, zero border-radius, dense newspaper columns. All are legitimate for some briefs, but they appear regardless of subject. Where the brief leaves an axis free, don't spend that freedom on a default. Name which (if any) you used and why it's a choice, not a reflex.

1. Typography carries personality. Pair display + body faces deliberately — not the families you'd reach

for on any project. Make the type treatment a memorable part of the design, not a neutral delivery vehicle.

1. Structure is information. Numbering, eyebrows, dividers, labels must encode something true about the

content, not decorate it. Numbered markers (01/02/03) are only right if the content actually is a sequence. Question every structural device before using it.

1. Motion, deliberate. Decide where/if animation serves the subject (page-load sequence, scroll reveal,

hover micro-interactions, ambient atmosphere). An orchestrated moment lands harder than scattered effects; sometimes less is more — extra animation reads as AI-generated.

1. Quality floor (the objective subset). Responsive down to mobile · visible keyboard focus · reduced

motion respected. Build to it without announcing it. (This trio is the accessibility floor quality-verification can check objectively.)

1. Restraint / one signature. Spend your boldness in one place; let the signature element be the one

memorable thing and keep everything around it quiet. Match complexity to the vision — maximalist needs elaborate execution, minimal needs precision. Cut any decoration that doesn't serve the brief.

1. Copy as design material. Words exist to make the design easier to understand and use — design material,

not decoration (see the writing section below).

The contract's ## Prototype section (the reference-spec mockup)

Alongside the seven rubric axes, the design contract carries one more stable section, ## Prototype. It names the committed reference-spec mockup and the bar Verify grades fidelity against:

## Prototype
- path: `docs/features//prototype/index.html` (committed in the TARGET project) — a reference spec, NOT shipped code
- meaning: production **re-implements** this mockup in the target's real stack; the HTML mockup itself never
  ships (degenerate exception: a target that genuinely is static HTML).
- fidelity bar: 

The single mockup the human agreed on in the visual companion (Phase 1) is the one promoted here to the committed prototype/index.html; the companion's throwaway screens are discarded. quality-verification reads this section in Verify to locate the mockup and grade the built UI's fidelity against it.

More on writing in design

Bring the same intentionality to copy as to spacing and color. Write from the end user's side of the screen: name things by what people control and recognize, never by how the system is built (a person manages notifications, not webhook config). Use active voice — a control says exactly what happens ("Save changes," not "Submit"); an action keeps its name through the whole flow (a "Publish" button produces a "Published" toast). Treat failure and emptiness as direction, not mood: errors explain what went wrong and how to fix it, in the interface's voice, never apologizing or vague; an empty screen is an invitation to act. Keep the register conversational and tuned — plain verbs, sentence case, no filler. Let each element do exactly one job.

Rationalizations

• "The brief didn't pin a direction, so I'll go cream + serif + terracotta — it always looks clean." → That

is exactly an AI default (cluster a). Free axes are where you make a CHOICE for this brief, not where you spend the freedom on a reflex.

• "Three variants is overkill, I'll just style the obvious card grid." → Then you skipped exploration. If

the look is genuinely open, structurally-different variants are how you find the non-obvious answer; "three tweaked card grids isn't a prototype, it's wallpaper."

• "I'll put the accessibility/responsive requirements in acceptance.md so quality-verification tests them." → No. ALL design

floors live in this contract; acceptance.md is behavioral-only. quality-verification reads the contract for the design gate.

• "The exploration variants are good code, I'll keep them around." → Exploration is throwaway. The throwaway

screens live in the gitignored .frontend-design/ working dir and are discarded; only the one agreed mockup survives — promoted to the named, committed reference-spec mockup docs/features//prototype/index.html, not rewritten from memory. (The ?variant= switcher is the escalation path, not a committed artifact.)

• "Not taking a risk is the safe move." → Not taking a risk is itself a risk; the client already rejected

templated proposals.

Red flags

• Variants that differ only in color or copy (a tweak, not a prototype — real variants disagree about

structure).

• Landing on one of the three AI-default clusters on a free axis without a stated reason.
• Numbered markers / eyebrows / dividers used as decoration on content that isn't actually a sequence.
• Design requirements written into acceptance.md instead of the contract.
• Shipping an exploration screen — or the committed reference-spec mockup HTML itself — straight to

production. Throwaway screens are discarded; the committed mockup is a reference spec that production re-implements in the real stack (it is not itself shipped, except a genuinely static-HTML target).

• Two or more competing "signature" elements (boldness not spent in one place).
• A design contract missing any of the seven stable sections or the ## Prototype section, or with the

quality-floor trio unaddressed.

Verification (ending criteria)

Done when ALL hold:

• Exactly ONE high-fidelity prototype is committed as the reference-spec mockup at

docs/features//prototype/index.html (the throwaway companion screens discarded from the gitignored .frontend-design/ working dir; the ?variant= switcher is the escalation path now, not a committed artifact); it runs and meets the quality floor (responsive · visible focus · reduced motion).

• A design contract exists with all seven stable sections filled (`Distinctiveness · Typography ·

Structure-as-information · Motion · Quality floor · Restraint · Copy-as-design-material) **plus the ## Prototype section naming the committed reference-spec mockup**, status: draft`, naming which AI-default cluster (if any) was used and why it's a choice.

• No design content leaked into acceptance.md (behavioral-only). The contract is the sole design

home.

• The contract is a separable artifact quality-verification can re-read cold in Verify (where the design gate binds).
• Handed to the human for sign-off at the Spec gate; on sign-off status: signed. (test-driven-development/quality-verification refuse an

unsigned or absent contract.)

Outputs & handoff contract

• Emits: (1) a committed high-fidelity prototype = the **reference-spec build target that production

re-implements, at docs/features//prototype/index.html; (2) the design contract — the 5th** signed Spec artifact (UI-only) — written to docs/features//design-contract.md.

• Stable sections (consumers depend on these names): `Distinctiveness · Typography ·

Structure-as-information · Motion · Quality floor (responsive/visible-focus/reduced-motion) · Restraint · Copy-as-design-material · Prototype (the committed reference-spec mockup + its fidelity bar); plus status: draft|signed. Change a section's shape → update quality-verification`'s design-gate reader in the same commit.

• Consumed by: quality-verification (Verify design gate: reads the ## Prototype section to locate the

committed reference-spec mockup and grades the built UI's fidelity against it, plus these seven axes), and gating `tes

…

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: celestialdust
• Source: celestialdust/achilles-skills
• License: MIT

Install and usage instructions live in the source repository linked above.