Design Engineering

Design Engineering Skill

Based on Emil Kowalski's design engineering philosophy — UI polish, component craftsmanship, and the compound value of invisible details.

Core Principles

• Taste is trainable. Develops through studying exceptional work, reverse-engineering animations, and intentional practice.
• Invisible details create love. Most UI refinements users never consciously register — but combined they produce something stunning.
• Beauty differentiates. When functionality is table stakes, aesthetic excellence becomes genuine leverage.

Anti-Slop Visual & Structural Checklist

Defaults that signal machine-generated UI ("AI slop"). Each is a falsifiable rule to uphold:

• Avoid full-bleed saturated gradient backgrounds (purple-to-pink/blue hero washes) and gradient headlines (background-clip: text). Use solid ink or warm neutral tinting.
• Avoid emoji as load-bearing decoration (emoji as icons, bullet markers, or section badges). Use a real icon set (Lucide/Phosphor/Heroicons) or typographic hierarchy.
• Avoid the 3-equal-column card grid with icon-above-heading tiles, nested cards-in-cards, or cards with thick coloured left-edge side stripes.
• Avoid hand-drawn fake imagery in SVG (synthetic "photos", invented logos, faux screenshots). Use a real asset or an honest labeled placeholder.
• Avoid fake re-drawn UI chrome (mock browser bars with traffic-light dots, mock IDE title bars, faux phone frames). Let content stand cleanly or use real screenshots in a <figure>.
• Avoid default-attractor sameness (Hero → 3 features → CTA → footer). Pick intentional macrostructures and vary heading placement, column rhythm, and divider language.
• Avoid the overused default font stack (Inter/Roboto on system-ui with no pairing). Apply the 2+1 rule (display + body + at most 1 outlier face in <=2 slots).
• Avoid italic headers: headings and display type are always roman (font-style: normal). Never use single-word italic emphasis inside a headline.

Pre-Emit Self-Critique (Six Axes)

Before marking any UI output complete, score it 1–5 on these six axes (score <3 on any axis triggers a revision pass):

The 8 Interactive States Discipline

Every interactive element (button, input, select, card, tab, switch) must explicitly handle all 8 states in code. Styling only default + hover is an immediate defect:

Input Fields & Zero Layout Shift

Input fields, textareas, and selects are where almost-right UIs break:

• Constant border width (1px everywhere): Never change border-width between default, hover, focus, error, or disabled states. State changes go to background-color, outline, box-shadow, or border-color.
• Reserved transparent outline: Initialize with outline: 2px solid transparent; outline-offset: 1px; so activating :focus-visible never shifts layout or thrashes paint.
• Matched component heights: Input height MUST equal adjacent button height (base floor 44px for touch targets).
• Reserved helper-text slot: Allocate min-height: 1lh for helper/error text so appearing validation messages do not push downstream page content.

Responsive Non-Negotiables

Verify every layout at 320px, 375px, 414px, and 768px:

• No horizontal scroll: Apply overflow-x: clip (never hidden) on both html and body.
• Single-line clickable affordances: Buttons, primary nav links, footer links, and CTAs must never wrap to two lines. Shorten label or reflow parent container.
• Image grid tracks: Always use minmax(0, 1fr) instead of bare 1fr to prevent image intrinsic dimensions from blowing out the grid.
• Header wrapping: Display headers must include overflow-wrap: anywhere; min-width: 0;.

Locked Tokens Discipline

• All colors and typography must bind to declared tokens (var(--color-accent), var(--font-display)).
• Never improvise inline hex / rgb / OKLCH values in components mid-build.
• Keep accent footprint under ~5% of viewport area (accent is for focal emphasis, not surface fill).
• Tint neutral surfaces toward the primary anchor hue (minimum 0.005 chroma in OKLCH) — avoid flat #000 / #fff.

Minimum-Scale Floors

Accessibility-grounded hard thresholds. Going below these is a defect, not a style choice:

Treat these as the lower bound, not the target. Captions and footnotes may approach the floor; primary content should sit comfortably above it.

Context-First & Pre-Flight Discipline

High-fidelity work MUST be rooted in real context before any pixels are produced:

• Run Pre-Flight Scan: Inspect existing design.md, package font stacks, palette tokens (:root, Tailwind @theme), motion libraries (framer-motion, motion, gsap), and spacing scale.
• Preserve existing design systems: Never overwrite established tokens or typography unless explicitly asked.
• Lift exact values: Copy real token variable names and spacing classes straight from source. Do NOT reconstruct token values from memory.

Question-Budget Gate

Calibrate questions to how bounded the ask is, then proceed:

• Rich context + bounded ask → ask nothing, build. Example: "match this card to the existing dashboard" with the repo in hand.
• Open ask → ask before building. Example: "prototype my onboarding" needs goals, target audience, and which dimension to diverge on (UX flow vs. visual treatment vs. copy). Resolve those three, then start.

Explore Many Variations

For exploratory or open work, produce 3+ atomic variations across distinct axes, never three tweaks of one idea:

• Vary on different dimensions: layout, color, type treatment, interaction model.
• Deliberately mix safe matches with at least one novel direction — do not converge early.
• Order them basic → advanced so the reviewer can scan the gradient (the "Design It Twice" premise extended past two).

Match Existing Vocabulary

When editing a live UI, conform to it instead of imposing a new style:

• Reverse-engineer the palette, interactive states (hover/active/disabled), motion timing, and shadow/card/density treatment.
• Match the copy tone too — terse product UI and chatty marketing copy are different vocabularies.
• A change that introduces a foreign style is a regression even when it looks good in isolation.

No-Filler Content

• Every element earns its place. No dummy stats, decorative sections, or lorem blocks added just to fill space. If a block has no purpose, cut it.
• Honest placeholder beats a bad fake. A labeled placeholder ("[product screenshot]") is better than an invented icon or hand-drawn fake image. Do NOT fabricate assets — ask for the real ones.

Animation Decision Framework

Frequency determines approach

Never animate keyboard-initiated actions — they repeat hundreds of times daily, making animation feel sluggish.

Purpose validation

Every animation requires justification: spatial consistency, state indication, explanation, user feedback, or preventing jarring transitions. "It looks cool" alone disqualifies frequent interactions.

Easing rules

Critical: Abandon default CSS easings. Use custom curves:

/* Punchy entrance */
transition-timing-function: cubic-bezier(0.23, 1, 0.32, 1);

Never use ease-in — it delays initial movement exactly when attention peaks, making interfaces feel sluggish.

Duration guidelines

UI animations should stay under 300ms. Speed perception matters as much as actual speed.

Component Patterns

Buttons must respond

button:active {
  transform: scale(0.97);
}

Tactile feedback confirming interface responsiveness.

Never scale from zero

/* Bad */
.enter { transform: scale(0); opacity: 0; }

/* Good — natural entrance */
.enter { transform: scale(0.95); opacity: 0; }

Real-world objects don't vanish and reappear. Start from scale(0.95).

Popovers scale from triggers

.popover {
  transform-origin: var(--radix-popover-content-transform-origin);
}

Exception: modals keep centered origin (viewport-anchored, not trigger-anchored).

Tooltip optimization

Initial tooltip includes delay; subsequent hovers skip both delay and animation via [data-instant] attribute — perceived speed without defeating accidental activation prevention.

Advanced Animation Techniques

For advanced transform mastery, 3D orbits, and clip-path animation recipes (tabs, hold-to-delete, image reveals, sliders), see reference/animation-recipes.md.

Performance Rules

GPU acceleration

Only animate transform and opacity — these skip layout and paint. Animating padding, margin, height, width triggers full rendering pipeline.

CSS variables caveat

Changing parent CSS variables recalculates styles on all children. Update transform directly on elements instead.

Framer Motion gotcha

Shorthand properties (x, y, scale) use main-thread requestAnimationFrame, not GPU:

// Bad — main thread
<motion.div animate={{ x: 100 }} />

// Good — GPU accelerated
<motion.div animate={{ transform: "translateX(100px)" }} />

CSS beats JavaScript

CSS animations run off-thread and remain smooth during page loads. Framer Motion drops frames when browser is busy. Use CSS for predetermined animations; JavaScript for dynamic, interruptible ones.

Accessibility

Reduced motion

Keep opacity and color transitions (aid comprehension). Remove movement and position animations:

@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

Touch hover protection

@media (hover: hover) and (pointer: fine) {
  .card:hover {
    transform: translateY(-2px);
  }
}

Touch triggers false hover positives — always gate hover animations.

Building Loved Components

For component craftsmanship principles (developer experience, defaults, edge cases, asymmetric timing), see reference/component-craft.md.

Review Checklist

Two-Stage Verification Handoff

Visual work ships through two passes, mirroring the toolkit's verification-before-completion and subagent two-stage review ethos:

1. Cheap self-check. Load the rendered result yourself, eyeball it, and fix the obvious breaks (broken layout, wrong token, console errors) before handing off. Never claim done on output you have not opened.
2. Independent verifier pass. A separate reviewer (or fresh subagent) does the deeper check — visual fidelity against source, layout under different widths, console clean. On pass it stays silent; it surfaces ONLY on failure, with the specific defect.

Anti-Patterns

• transition: all — animates unintended properties, hurts performance
• ease-in on UI elements — delays feedback when attention peaks
• Animating height/width/margin — triggers layout recalculation
• Same duration for enter and exit — exits should be faster
• Hover effects without @media (hover: hover) — breaks touch devices
• Framer Motion shorthands under load — drops frames on main thread

Rules

• MUST specify exact properties in transition (transition: transform 200ms ease-out) — never transition: all
• MUST use ease-out (or a custom curve) on UI appearances; ease-in delays feedback at the moment the user's attention peaks
• NEVER animate height, width, margin, or top/left — animate transform and opacity only
• CRITICAL: exit is faster than enter. A 2s linear enter (hold-to-delete) needs a 200ms ease-out exit
• MANDATORY: any animation longer than 300ms for UI feedback needs an explicit justification
• MUST implement all 8 interactive states (default, hover, focus-visible, active, disabled, loading, error, success) for every interactive element
• MUST keep border-width: 1px constant across all input states (default/hover/focus/error/disabled) with a reserved transparent outline to guarantee zero layout shift
• MUST apply overflow-x: clip on both html and body to eliminate horizontal viewport scrolling on mobile (320px–768px)
• MUST ensure clickable affordance text (buttons, nav links, CTAs) remains single-line across all viewports
• MUST keep all display headings roman (font-style: normal) — never use single-word italic emphasis inside headlines
• MUST adhere to the 2+1 typography rule (max 3 families, outlier face used in at most 2 slots)
• MUST lock all colors to named CSS variable tokens — never improvise inline hex/rgb/OKLCH values mid-render
• MUST lift exact values (hex, spacing, font stack, radii) from real source — never reconstruct tokens from memory
• MUST keep mobile touch targets at 44px+ minimum floor
• NEVER ship slop defaults (purple/blue gradient hero washes, gradient text headlines, emoji as icons, cards-in-cards, side-stripe cards, centered-everything 100vh heroes)
• NEVER add filler (dummy stats, fake testimonials, invented logos, lorem) — use honest labeled placeholders
• MUST run pre-emit self-critique scoring (P/H/E/S/R/V) before completing UI implementation

Gotchas

For compositor edge cases, Framer Motion GPU optimizations, and reduced-motion gotchas, see reference/animation-recipes.md.

When NOT to Load

• For accessibility beyond motion (contrast, focus, ARIA) — use /a11y-validate
• For component-library architecture (Radix, Headless UI, ShadCN) — use /frontend-specialist agent
• For information architecture and user flows — use /ux-designer agent
• For generic CSS patterns without motion — this skill is motion-specific
• For brand voice / content tone — use /brand-voice