Frontend Design

Make websites feel premium and trustworthy — based on peer-reviewed research, not aesthetic opinions.

Core Principles

The brain uses processing fluency as a shortcut: "easy to process = probably true/safe/good" (Reber & Schwarz 1999). Users form stable judgments within 50ms (Tuch et al. 2012). Two factors drive that judgment:

1. Low visual complexity — fewer competing elements, clear hierarchy
2. High prototypicality — looks like what the user expects for this category of site

This triggers a halo chain (Tractinsky 2000):

Readable + Clean + Predictable → fluent → "beautiful" → perceived usable → perceived trustworthy

Four measurable properties of "premium feel":

Property	Meaning
Readability	Text and structure effortless to parse
Smoothness	Nothing breaks the user's flow; animations are flawless or absent
Predictability	Site behaves like the user expects for its category
Cleanliness	No competing elements, clear visual hierarchy

Trust is also built by factors beyond visual design (Stanford, NNGroup, Baymard): real organization proof, easy contact, upfront pricing, zero errors, external reviews, no hidden costs. Visual "premium-ness" overdone reduces trust by looking like a scam trying too hard.

General rule: All details, even the smallest, should be cared for. Visual clarity is one part of it.

Mode Selection

When this skill is invoked, determine the operating mode:

• If the user is building or writing frontend code → Active Guidance
• If the user is reviewing, auditing, or checking existing code → Audit
• If ambiguous → ask:

"Should I apply design guidance while we build, or audit existing code for problems and suggestions?"

Active Guidance Mode

Apply research-backed design practices while generating frontend code. The goal is correct output, not commentary.

Process

1. Read practices.md for the category index, then read the relevant category guides for the current task
2. While generating code, silently apply the relevant practices:
   • Accessibility: contrast, focus states, ARIA, heading hierarchy
   • Typography: line length, font size, hierarchy, fluid scaling
   • Spacing: consistent scale, container padding
   • Color: semantic roles, predictable usage, primary reserved for primary actions
   • Motion: CSS-first, 150-300ms micro, 400ms max complex, prefers-reduced-motion
   • Performance: lazy loading, code splitting, animate only transform/opacity
   • States: skeleton loaders, error messages with cause + fix, empty states with action
   • Responsive: mobile-first, touch targets >= 44px, no horizontal scroll
   • Forms: visible labels, validate on blur, progressive disclosure
3. If you need a specific implementation pattern → read patterns.md
4. If the user's request conflicts with a research-backed practice → mention the conflict briefly, follow the user's instruction
5. If the user's request matches a known opinionated claim → check warnings.md, note it's opinion not research, follow the user's instruction
6. Do not lecture. Produce correct code.

What NOT to do in active guidance

• Do not explain every design decision unless asked
• Do not refuse user requests based on the checklist — note conflicts, then comply
• Do not prescribe specific fonts, colors, or hex values — those are project-specific
• Do not assume dark or light mode — match the project's existing theme

Audit Mode

Scan existing frontend code for problems, then provide improvement suggestions. The fewer problems found, the more focus shifts to suggestions.

Process

1. Read practices.md for the category index, then read the relevant category guides
2. Read report-format.md for the output template
3. Phase 1 — Checklist Pass: Scan the code against the checklist in each relevant category guide
   • For each violation: note file location, what's wrong, which practice it violates
   • Classify severity: critical (harms trust/accessibility/usability), warning (reduces quality), note (minor)
4. Phase 2 — Suggestions Pass: Apply the core principles above to find improvement opportunities
   • Look for areas where readability, smoothness, predictability, or cleanliness could improve
   • Check trust signals (§14 in practices.md) — are organizational proof, contact info, upfront pricing present?
   • If few problems were found in Phase 1, expand this section
5. Check warnings.md — flag any opinionated patterns found in the code
6. Produce the report following the template from report-format.md
7. If the user asked only for problems or only for suggestions, respect that

Quick Reference

The most critical items across all categories. Full checklists in practices.md.

Accessibility (WCAG)

• Contrast: >= 4.5:1 body, >= 3:1 large text
• Focus: visible focus-visible rings on all interactive elements
• Motion: prefers-reduced-motion disables non-essential animation
• Headings: sequential h1 → h2 → h3, no level skip
• Icons: aria-label on every icon-only button

Typography (Processing Fluency)

• Line length: 55-75 chars desktop, 35-45 mobile
• Min body size: 16px mobile
• Line height: 1.5-1.75
• Max 2 font families + monospace for data
• Fluid scale via clamp()

Color (Predictability)

• Every color has a semantic role (primary, accent, semantic, neutral, surface)
• Primary reserved for primary actions only
• Active states expressed via border/shadow/weight — NOT primary color background
• Color matches industry expectations

Motion (Smoothness)

• 150-300ms micro, 400ms max complex
• CSS-first, JS only when needed
• Only animate transform and opacity
• Janky > remove it. Only ship what runs flawlessly.

Performance (Trust)

• Lazy load below-fold, code split by route
• font-display: swap, preload critical fonts only
• Reserve space for async content (prevent CLS)
• JS budget: < 500KB desktop, < 150KB mobile

States (Care for Details)

• Skeleton loaders for > 300ms waits
• Error messages: cause + how to fix
• Empty states: helpful message + action

Trust Signals (Research)

• Real org proof: address, team bios, photos
• Easy contact: phone, email, address prominent
• Upfront pricing: no hidden costs, no login walls
• External validation: third-party reviews, press
• Zero errors: typos and broken links destroy credibility
• Max 5 trust badges — more creates suspicion

Reference Files

File	When to read
practices.md	Both modes — index of 14 categories, each linking to a detailed guide with checklist + guidance + common mistakes
report-format.md	Audit mode — output template with severity tiers
patterns.md	When you need a specific code implementation
warnings.md	When checking if design advice is opinion vs research

Red Flags

Stop and reconsider if you find yourself:

• Prescribing specific fonts or colors as universally "premium"
• Recommending dark mode as inherently more trustworthy
• Breaking prototypicality (category-standard layouts) for "originality"
• Adding animations that haven't been tested for smoothness
• Using primary color for active states on non-primary elements
• Ignoring trust signals (§14) while perfecting visual details
• Lecturing the user about design theory instead of producing code

Verification

After completing work in either mode:

• No opinionated claims presented as fact
• Accessibility basics covered (contrast, focus, ARIA, motion)
• Typography readable (line length, size, hierarchy)
• Color usage predictable (semantic roles, primary reserved for actions)
• Motion is flawless or absent — nothing janky
• Performance considered (lazy loading, code splitting, CLS prevention)
• Every state handled (loading, error, empty)
• Trust signals addressed or noted as missing