---

name: web-design-standards-review description: Evaluate and apply modern web design principles using web standards (W3C/WHATWG) and authoritative guidance (MDN, web.dev). Covers mobile-first, fluid layouts, CSS logical properties, feature detection (vs UA/version sniffing), progressive enhancement, accessibility (WCAG), internationalization, semantics, and performance-oriented UX. license: CC-BY-4.0 compatibility: Works in any web-frontend environment; assumes access to HTML/CSS/JS and standard browser devtools. metadata: version: "1.0" author: "community-template"

Web Design Standards Review

Use this skill when you need to define, justify, or review web UI design/implementation principles with a focus on:

• Web standards (W3C/WHATWG specs) vs
• Authoritative guidance (MDN, web.dev, W3C WAI)

Your goal is to produce decisions that are robust across devices, input methods, writing directions, and user settings (zoom, font-size, high contrast), and to avoid brittle heuristics (e.g., browser/version sniffing).

Output contract

When you apply this skill, return:

1. Decision for each principle: Recommend / Recommend with constraints / Discourage
2. Rationale by category
   • Standard: a capability/behavior defined by a spec (e.g., CSS Grid, Media Queries, CSS Logical Properties)
   • Guidance: best practices (e.g., progressive enhancement, content-driven breakpoints)
   • Heuristic: experience-based advice that may not be formally standardized
3. Scope & exceptions
4. Implementation guidance (prefer concrete patterns/snippets)
5. Review checklist
6. References (prefer W3C/WHATWG, then MDN/web.dev/WAI)

If the user asks "Is this a standard?", be strict: the principle is usually guidance, while the tools (CSS/HTML/JS features) are standards.

---

Principles

1) Mobile-first over desktop-first

Decision: Recommend (Guidance)

Intent: Establish a baseline UX that works on small screens and constrained conditions; then enhance for larger viewports and richer input.

Implementation guidance

• Start with a simple single-column baseline and progressive enhancement for larger screens.
• Use content-driven breakpoints rather than targeting specific devices.
• Ensure tap targets and readable typography at the baseline.

Exceptions

• Desktop-only specialist apps where high-density workflows are an explicit requirement. Even then, ensure accessibility and resilience for zoom/font scaling.

---

2) Fluid/relative layout over pixel-perfect fixed layout

Decision: Recommend (Guidance + Standards as enablers)

Intent: Layout should adapt to viewport size, zoom, font-size changes, and translated text length.

Implementation guidance

• Prefer modern layout primitives: Flexbox and Grid.
• Use relative units for sizing and spacing: %, em, rem, vw, vh, and consider clamp() for responsive typography.
• Prefer intrinsic sizing and min/max constraints over hard-coded pixel widths.

Exceptions

• Pixel-precise surfaces where the content itself is pixel-addressed (e.g., bitmap editors, some games/canvas UIs). Isolate these areas and keep the surrounding UI fluid.

---

3) Logical direction over physical direction (I18N-ready layout)

Decision: Recommend (Standard + Guidance)

Intent: Support RTL languages and alternate writing modes (e.g., vertical writing) without rewriting layout rules.

Implementation guidance

• Replace left/right/top/bottom-anchored rules with CSS Logical Properties:
  • margin-inline-start/end, padding-inline-start/end
  • inset-inline-start/end (instead of left/right)
  • border-inline-start/end-*, etc.
• Prefer direction-aware values where available:
  • text-align: start/end (instead of left/right)
• Test with dir="rtl" and at least one non-Latin locale; validate overflow and truncation behavior.

Migration strategy

• Start with shared primitives (spacing, layout wrappers, components) and new code.
• Migrate high-impact screens next; avoid “big bang” replacements unless you have strong automated visual regression coverage.

---

4) Feature detection over browser/version detection (UA sniffing)

Decision: Recommend (Guidance)

Intent: Use capabilities, not identities. Browser/version detection breaks under UA reduction and is brittle across forks and compatibility layers.

Implementation guidance

• CSS
  • @supports (property: value) { ... }
  • CSS.supports("property", "value")
• JavaScript
  • if ("serviceWorker" in navigator) { ... }
  • if (typeof IntersectionObserver === "function") { ... }
  • Prefer try/catch around feature use for runtime-guarding when appropriate.

Exceptions (narrow and justified)

• Analytics/telemetry (non-functional behavior)
• Known, severe, vendor-specific bugs with documented, time-bounded workarounds
• Even then, prefer capability-based alternatives (e.g., Client Hints / UA-CH where supported) and document why.

---

5) Progressive enhancement as the default strategy

Decision: Recommend (Guidance)

Intent: A working baseline first; enhancements layered by capability.

Typical pattern

1. Baseline: semantic HTML + minimal CSS that yields a usable page.
2. Enhance: richer layout (Grid/Flex), advanced styling, optional JS behaviors.
3. Guard: apply enhancements using feature detection (@supports, runtime checks).
4. Fallback: ensure critical flows remain possible without the enhancement.

Accessibility implication Progressive enhancement pairs naturally with accessibility: if you start from semantic HTML, assistive technologies and keyboard interaction are far more likely to “just work”.

---

Cross-cutting principles (always consider)

Accessibility (WCAG-aligned)

• Keyboard support and visible focus
• Adequate color contrast
• Alternative text for meaningful images
• Clear headings/landmarks and form labels
• Error states: explain and recover

Rule of thumb: Use native HTML semantics first, add ARIA only when necessary.

Semantics & structure

• Separate meaning (HTML) from presentation (CSS) and behavior (JS).
• Avoid using divs for everything when a semantic element exists; it impacts navigation and accessibility.

Internationalization & localization (I18N/L10N)

• Expect text expansion/contraction; avoid fixed-width containers that rely on English copy lengths.
• Avoid embedding text in images.
• Support locale formats (dates, numbers, currency) and ensure fonts cover required glyphs.

Performance as UX

• Optimize for “usable quickly”:
  • avoid unnecessary JS
  • optimize images/fonts
  • measure user-centric metrics (e.g., Core Web Vitals concepts)
• Prefer resilient UI under slow networks and low-end devices.

Resilience

• Don’t break under:
  • zoom and increased font-size
  • high-contrast or reduced motion preferences
  • intermittent network/offline states
• Design empty/error/loading states intentionally.

---

Review checklist

• Baseline UI works on small screens and constrained conditions (mobile-first mindset)
• Layout is fluid: survives zoom and font-size changes (relative units + modern layout)
• Direction is logical: can flip dir to RTL without breaking core layout
• No UA/version sniffing for functionality; uses feature detection and guards
• Progressive enhancement is explicit: enhancements are optional layers
• WCAG considerations covered (keyboard, focus, contrast, text alternatives, forms)
• I18N doesn’t break layout (text length, locale formatting, fonts)
• Performance budgets and measurements exist (esp. images/fonts/JS)

---

Examples

Example: Replace UA sniffing with feature detection

Bad

Copyif (navigator.userAgent.includes("Safari/") && !navigator.userAgent.includes("Chrome/")) {
  // do X
}

Better

Copyif ("serviceWorker" in navigator) {
  // do X
} else {
  // fallback behavior
}

Example: Replace physical with logical properties

Bad

Copy.card {
  padding-left: 16px;
  border-left: 4px solid currentColor;
}

Better

Copy.card {
  padding-inline-start: 1rem;
  border-inline-start: 0.25rem solid currentColor;
}

See references/REFERENCE.md for curated standards and guidance links.