Design Engineer

Design Engineer Audit

Audit and apply design engineering craft to frontend codebases. Rooted in the work of two practitioners:

• Jhey Tompkins (jh3y) — Staff Design Engineer at Shopify. Pushes the boundaries of CSS with scroll-driven animations, anchor positioning, the Popover API, @property hacks, 3D transforms, and creative interaction patterns. Turns complex UI challenges into approachable, delightful solutions.
• Jakub Krehel — Founding Design Engineer at Interfere. Obsesses over the smallest details: concentric border radii, optical alignment, OKLCH color, shadows as borders, staggered enter animations, and shared layout transitions. Makes people feel something through craft.

How to Use

• /design-engineer — Run a full audit against all five lenses on the current project
• /design-engineer <file-or-pattern> — Audit specific files
• /design-engineer fix — Audit and apply fixes directly

Audit Process

1. Discover

Scan the codebase for UI files (HTML, CSS, JSX, TSX, Vue, Svelte, etc.). Identify components, pages, layouts, and style files.

2. Audit Through Five Lenses

Evaluate every UI surface against these five design engineering lenses. Each lens has a dedicated reference file with detailed patterns and code examples.

Lens 1: Optical Refinement

Reference: references/optical-refinement.md

Detect and fix visual misalignments the eye catches but the spec misses:

• Concentric border radii — Nested rounded elements must subtract padding from the outer radius. inner_radius = outer_radius - padding. Mismatched curvature looks careless.
• Shadows over borders — box-shadow: inset 0 0 0 1px renders subpixel and blends with backgrounds. Hard border adds layout-affecting pixels and looks heavy.
• Optical alignment — Center icons and text visually, not mathematically. Play buttons need padding-left nudges. Rounded shapes in square containers need optical centering.
• Consistent spacing rhythm — Spacing should follow a scale (4px base). Irregular gaps between siblings break visual rhythm.
• Border radius consistency — Related elements sharing a visual group must use matching or concentric radii, never arbitrary values.

Lens 2: Motion & Animation

Reference: references/motion-and-animation.md

Choreograph motion that guides attention and communicates state:

• Staggered enter animations — Break components into parts (title, description, actions). Animate each with opacity + translateY + blur, staggered by 60-100ms. Never animate a container as one block.
• Scroll-driven animations — Replace JS scroll listeners with CSS animation-timeline: scroll() and animation-timeline: view(). Highlight text, parallax layers, progress indicators — all without JavaScript.
• @property for animatable custom properties — Register custom properties with @property to animate values CSS normally cannot interpolate (numbers, colors, percentages).
• Exit animations — Elements that enter with animation must exit with animation. Use AnimatePresence, the @starting-style rule, or transition-behavior: allow-discrete for display/overlay transitions.
• prefers-reduced-motion — Always wrap motion in @media (prefers-reduced-motion: no-preference). Provide static fallbacks.

Lens 3: Color & Depth

Reference: references/color-and-depth.md

Build color systems that are perceptually uniform and create visual depth:

• OKLCH color space — Define colors in oklch(L C H). Manipulate lightness and chroma independently without hue shifts. Generate harmonious palettes by rotating the hue channel.
• Perceptual uniformity — Two colors with the same L value in OKLCH appear equally bright. HSL cannot guarantee this. Use OKLCH for accessible contrast calculations.
• Layered depth — Build depth through multiple box-shadow layers (ambient + direct + contact), translucent overlays, and subtle background gradients rather than flat solid fills.
• Gradient craft — Gradients must not band. Use OKLCH interpolation (in oklch) for smooth perceptual transitions. Add subtle noise textures to kill banding.

Lens 4: Modern CSS Patterns

Reference: references/modern-css-patterns.md

Replace JavaScript workarounds with native CSS features:

• CSS Anchor Positioning — Position tooltips, popovers, and dropdowns relative to their trigger with anchor-name and position-anchor. No JS positioning libraries needed.
• Popover API — Use popover attribute for toggle-able UI: menus, tooltips, drawers. Built-in light-dismiss, top-layer stacking, keyboard handling. Pair with anchor positioning.
• View Transitions API — Animate between page states or route changes with document.startViewTransition(). Add view-transition-name to morph specific elements across states.
• Container Queries — Size components to their container with @container, not the viewport. Every reusable component should be container-aware.
• @starting-style — Define the initial style for elements entering the DOM so transition works on first render. Essential for animating display: none to display: block.

Lens 5: Interaction Delight

Reference: references/interaction-delight.md

Add moments of surprise that reward engagement:

• Cursor-aware effects — Track cursor position with CSS custom properties via minimal JS. Drive parallax, light sources, card tilts, and reveal effects from --mouse-x / --mouse-y.
• Clip-path interactions — Use clip-path for hold-to-confirm buttons, circular reveals, and morphing shapes. clip-path transitions are GPU-accelerated and silky smooth.
• Shared layout animations — When an element appears in two states (list item to detail, thumbnail to hero), animate the transition with FLIP technique or Motion's layoutId. Never hard-cut between related views.
• Whimsical form feedback — Replace generic validation with character: shaking inputs, color-shifting borders, confetti on success. Small personality in forms builds trust.
• Hover state depth — Hover should reveal, not just highlight. Scale subtle transforms (1.01-1.03), shift shadows, reveal hidden content, or trigger micro-animations.

3. Report

For each finding, output:

[LENS] file:line — Issue description
  WHY: Why this matters (1 sentence)
  FIX: Concrete code change

Group findings by lens. Prioritize highest-impact items first within each lens.

4. Apply (when fix mode)

When applying fixes:

• Make the smallest change that achieves the effect
• Preserve existing code style and conventions
• Test that fixes don't break layout or functionality
• Add will-change only during active animations, never statically
• Respect the project's existing animation library (Motion, GSAP, CSS) rather than introducing new dependencies

Severity Levels

• CRAFT — Optical misalignment, missing concentric radii, inconsistent spacing. Feels unpolished.
• MOTION — Missing enter/exit animations, jarring state changes, no stagger. Feels static.
• MODERN — JavaScript used for something CSS handles natively. Unnecessarily heavy.
• DELIGHT — Missed opportunity for a moment of surprise or personality. Feels generic.

Principles

1. Sweat the details humans notice — Mismatched curves, jumpy transitions, and dead hover states erode trust subconsciously.
2. Choreograph, don't animate — Every moving element should have a reason, a direction, and a relationship to other elements in motion.
3. CSS-first, JS-last — Reach for native CSS features before JavaScript. They are faster, more accessible, and more resilient.
4. Perceptual over mathematical — Optical centering beats geometric centering. OKLCH beats HSL. The eye is the final judge.
5. Earn delight through restraint — One perfectly timed staggered reveal is worth more than twenty bouncing elements. Delight comes from precision, not quantity.