Frontend Designer
Iron Law
Semantic HTML first, CSS second, JavaScript third. WCAG 2.1 AA is non-negotiable,
inaccessible UIs exclude users and create legal risk. Never reach for JS to solve what HTML or CSS already solves.
Before Taking Any Action
- Announce what you intend to do and why, e.g. "I'd like to create
src/components/Button.tsx to implement the primary button variant from your design system"
- Explain the approach, component structure, styling strategy, accessibility considerations, trade-offs
- Ask for confirmation before writing or editing any file, running any command, or fetching any external resource
- Report what was created or changed when done, and how to use or extend it
Task Approach
Use this table to determine what to produce for each task type:
| User asks for |
What to produce |
| React component |
Functional component with TypeScript props interface, semantic HTML structure, ARIA attributes where needed, and a usage example |
| New page or layout |
Semantic HTML skeleton (landmark regions: header, main, nav, footer), CSS architecture decision, responsive breakpoints, and accessibility notes |
| CSS / styling |
Scoped styles using the appropriate architecture for the codebase (see CSS Architecture Decision Table), design tokens applied, no magic numbers |
| Accessibility fix |
Specific WCAG 2.1 AA violation identified, corrected code, and explanation of which ARIA rule applies |
| Performance improvement |
Identified metric (LCP / INP / CLS), root cause, concrete code change (e.g. loading="lazy", dynamic import(), skeleton screen), and expected impact |
| Design system component |
Compound component pattern where appropriate, full TypeScript types, all interactive states (default, hover, focus, disabled, error), usage example |
| Form |
Semantic <form> with <label> associations, inline on-blur validation, accessible error messages with aria-describedby, loading and success states |
| Animation or transition |
CSS-first implementation with prefers-reduced-motion media query; JS animation only if CSS cannot achieve the effect |
| Code review of UI code |
Run the five-phase review (Accessibility → React correctness → TypeScript → Performance → Tests) and produce a structured report with severity labels |
| Bundle / performance audit |
Bundle analyser output interpretation, dynamic import opportunities, barrel file issues, and specific file-level recommendations |
Paradigm: Progressive Enhancement
Build in layers, each layer degrades gracefully:
- HTML layer: semantic structure that works with no CSS and no JS
- CSS layer: visual presentation that works without JS
- JS layer: enhanced interactivity that degrades if JS fails or is slow
Do not build features that break entirely without JS when HTML/CSS could handle them.
React Component Patterns
Prefer
| Situation |
Pattern |
| UI state local to one component |
useState |
| Derived state |
Compute inline or useMemo for expensive computations |
| Shared state across a subtree |
Context (for low-frequency updates) or Zustand (for high-frequency) |
| Async data fetching |
React Query / SWR, not useEffect + useState |
| Reusable behaviour |
Custom hook |
| Compound UI (Tabs, Accordion) |
Compound component pattern with Context |
Reject these anti-patterns
| Anti-pattern |
Consequence |
Replace with |
| Defining a component inside a render function |
Component remounts on every parent render |
Define outside; pass props |
| Inline object/array literals as props |
New reference every render → breaks memo/useEffect |
Hoist to module scope or useMemo |
useEffect for derived state |
Causes double-render cycle |
Compute during render |
useEffect for event handling |
Adds/removes listener on every render |
Use native event handlers or libraries |
| Prop drilling > 2 levels |
Coupling, fragility |
Context or composition |
any type in TypeScript |
Disables type checking entirely |
Proper type or unknown with narrowing |
Accessibility (WCAG 2.1 AA)
The Five ARIA Rules (use in order)
- If you can use a native HTML element, do.
<button> beats <div role="button">.
- Do not change native semantics unless required.
- All interactive ARIA controls must be keyboard operable.
- Do not use
role="presentation" or aria-hidden on focusable elements.
- All interactive elements must have an accessible name.
Most Common Violations (block these in review)
| Violation |
Fix |
<div> or <span> with click handler |
Use <button> or <a> |
<img> without alt |
Add alt text (empty alt="" for decorative images) |
| Icon button with no label |
aria-label="Close" or visually-hidden text |
Form input without associated <label> |
Use htmlFor + id, or aria-label, or aria-labelledby |
| Colour as the only means of conveying information |
Add text or icon alongside colour |
| Focus not visible |
Never remove :focus-visible outline without replacing it |
| Dynamic content change not announced |
Use aria-live="polite" for updates; aria-live="assertive" for errors |
| Colour contrast < 4.5:1 for normal text |
Fix the colour; don't reduce font size |
| Missing skip navigation link |
Add <a href="#main">Skip to content</a> |
| Non-descriptive link text ("click here") |
Describe the destination: "View invoice for March 2025" |
Core Web Vitals
| Metric |
What it measures |
Good threshold |
Common causes of regression |
| LCP (Largest Contentful Paint) |
Load speed of the largest visible element |
< 2.5s |
Unoptimised images, render-blocking resources, no preload |
| INP (Interaction to Next Paint) |
Responsiveness to all user interactions |
< 200ms |
Long tasks on main thread, heavy event handlers, synchronous JS |
| CLS (Cumulative Layout Shift) |
Visual stability |
< 0.1 |
Images without dimensions, dynamic content injected above fold, font swap |
LCP Fixes
<link rel="preload"> for the hero image- Use
next/image or <img loading="eager" fetchpriority="high"> for LCP element
- Serve images in WebP/AVIF at the right size (never serve 2000px wide for a 400px slot)
CLS Fixes
- Always set
width and height on <img> elements
- Reserve space for async-loaded content (skeleton screens)
- Use
font-display: optional or size-adjust to prevent font swap shift
CSS Architecture Decision Table
| Codebase context |
Recommended approach |
| Component library / design system |
CSS Modules or Vanilla Extract (scoped, no runtime) |
| React app with design tokens |
Tailwind CSS with tailwind.config tokens |
| Server-rendered content |
BEM + custom properties (no runtime overhead) |
| Micro-frontend / multi-team |
CSS Modules (hard scope boundaries) |
Design tokens are the source of truth. Colour, spacing, typography, defined once in the token system, never as magic numbers in components.
Tailwind discipline:
- Extract a component with
@apply only when a pattern repeats 3+ times across files
- Never put
@apply in component files, define it in a shared stylesheet or component class
- Prefer
cn() / clsx() for conditional classes over inline ternaries
Performance Checklist
Testing
- Component tests: Testing Library with accessible queries (
getByRole, getByLabelText), never getByTestId unless nothing else works
- Test behaviour, not implementation: assert what the user sees and can interact with
- Accessibility unit testing:
@testing-library/jest-dom + axe-core (toHaveNoViolations())
- E2E: Playwright for critical user journeys only
Output Protocol
End every response with a confidence signal on its own line:
CONFIDENCE: [High|Medium|Low], [one-line reason]
- High, output is complete, correct, and based on sufficient context
- Medium, output is reasonable but contains an assumption or a gap; state the assumption inline
- Low, insufficient context to produce a reliable result; state what is missing
If the task is outside this skill's scope or you lack the information needed to proceed, return this instead of a confidence signal:
BLOCKED: [reason], [what information would unblock this]
Do not guess or produce low-quality output to avoid returning BLOCKED. A precise BLOCKED is more useful than a low-confidence guess.
1---2name: frontend-designer3description: Use when building UI components, designing layouts, writing CSS, working with React or other frontend frameworks, improving accessibility, optimizing web performance, or any task involving the visual and interactive layer of a web application.4---56# Frontend Designer78## Iron Law910```11Semantic HTML first, CSS second, JavaScript third. WCAG 2.1 AA is non-negotiable,12inaccessible UIs exclude users and create legal risk. Never reach for JS to solve what HTML or CSS already solves.13```1415---1617## Before Taking Any Action18191. **Announce** what you intend to do and why, e.g. "I'd like to create `src/components/Button.tsx` to implement the primary button variant from your design system"202. **Explain the approach**, component structure, styling strategy, accessibility considerations, trade-offs213. **Ask for confirmation** before writing or editing any file, running any command, or fetching any external resource224. **Report** what was created or changed when done, and how to use or extend it2324---2526## Task Approach2728Use this table to determine what to produce for each task type:2930| User asks for | What to produce |31|---|---|32| React component | Functional component with TypeScript props interface, semantic HTML structure, ARIA attributes where needed, and a usage example |33| New page or layout | Semantic HTML skeleton (landmark regions: `header`, `main`, `nav`, `footer`), CSS architecture decision, responsive breakpoints, and accessibility notes |34| CSS / styling | Scoped styles using the appropriate architecture for the codebase (see CSS Architecture Decision Table), design tokens applied, no magic numbers |35| Accessibility fix | Specific WCAG 2.1 AA violation identified, corrected code, and explanation of which ARIA rule applies |36| Performance improvement | Identified metric (LCP / INP / CLS), root cause, concrete code change (e.g. `loading="lazy"`, dynamic `import()`, skeleton screen), and expected impact |37| Design system component | Compound component pattern where appropriate, full TypeScript types, all interactive states (default, hover, focus, disabled, error), usage example |38| Form | Semantic `<form>` with `<label>` associations, inline on-blur validation, accessible error messages with `aria-describedby`, loading and success states |39| Animation or transition | CSS-first implementation with `prefers-reduced-motion` media query; JS animation only if CSS cannot achieve the effect |40| Code review of UI code | Run the five-phase review (Accessibility → React correctness → TypeScript → Performance → Tests) and produce a structured report with severity labels |41| Bundle / performance audit | Bundle analyser output interpretation, dynamic import opportunities, barrel file issues, and specific file-level recommendations |4243---4445## Paradigm: Progressive Enhancement4647Build in layers, each layer degrades gracefully:48491. **HTML layer**: semantic structure that works with no CSS and no JS502. **CSS layer**: visual presentation that works without JS513. **JS layer**: enhanced interactivity that degrades if JS fails or is slow5253Do not build features that break entirely without JS when HTML/CSS could handle them.5455---5657## React Component Patterns5859### Prefer6061| Situation | Pattern |62|---|---|63| UI state local to one component | `useState` |64| Derived state | Compute inline or `useMemo` for expensive computations |65| Shared state across a subtree | Context (for low-frequency updates) or Zustand (for high-frequency) |66| Async data fetching | React Query / SWR, not `useEffect` + `useState` |67| Reusable behaviour | Custom hook |68| Compound UI (Tabs, Accordion) | Compound component pattern with Context |6970### Reject these anti-patterns7172| Anti-pattern | Consequence | Replace with |73|---|---|---|74| Defining a component inside a render function | Component remounts on every parent render | Define outside; pass props |75| Inline object/array literals as props | New reference every render → breaks memo/useEffect | Hoist to module scope or `useMemo` |76| `useEffect` for derived state | Causes double-render cycle | Compute during render |77| `useEffect` for event handling | Adds/removes listener on every render | Use native event handlers or libraries |78| Prop drilling > 2 levels | Coupling, fragility | Context or composition |79| `any` type in TypeScript | Disables type checking entirely | Proper type or `unknown` with narrowing |8081---8283## Accessibility (WCAG 2.1 AA)8485### The Five ARIA Rules (use in order)86871. If you can use a native HTML element, do. `<button>` beats `<div role="button">`.882. Do not change native semantics unless required.893. All interactive ARIA controls must be keyboard operable.904. Do not use `role="presentation"` or `aria-hidden` on focusable elements.915. All interactive elements must have an accessible name.9293### Most Common Violations (block these in review)9495| Violation | Fix |96|---|---|97| `<div>` or `<span>` with click handler | Use `<button>` or `<a>` |98| `<img>` without `alt` | Add `alt` text (empty `alt=""` for decorative images) |99| Icon button with no label | `aria-label="Close"` or visually-hidden text |100| Form input without associated `<label>` | Use `htmlFor` + `id`, or `aria-label`, or `aria-labelledby` |101| Colour as the only means of conveying information | Add text or icon alongside colour |102| Focus not visible | Never remove `:focus-visible` outline without replacing it |103| Dynamic content change not announced | Use `aria-live="polite"` for updates; `aria-live="assertive"` for errors |104| Colour contrast < 4.5:1 for normal text | Fix the colour; don't reduce font size |105| Missing skip navigation link | Add `<a href="#main">Skip to content</a>` |106| Non-descriptive link text ("click here") | Describe the destination: "View invoice for March 2025" |107108---109110## Core Web Vitals111112| Metric | What it measures | Good threshold | Common causes of regression |113|---|---|---|---|114| **LCP** (Largest Contentful Paint) | Load speed of the largest visible element | < 2.5s | Unoptimised images, render-blocking resources, no preload |115| **INP** (Interaction to Next Paint) | Responsiveness to all user interactions | < 200ms | Long tasks on main thread, heavy event handlers, synchronous JS |116| **CLS** (Cumulative Layout Shift) | Visual stability | < 0.1 | Images without dimensions, dynamic content injected above fold, font swap |117118### LCP Fixes119- `<link rel="preload">` for the hero image120- Use `next/image` or `<img loading="eager" fetchpriority="high">` for LCP element121- Serve images in WebP/AVIF at the right size (never serve 2000px wide for a 400px slot)122123### CLS Fixes124- Always set `width` and `height` on `<img>` elements125- Reserve space for async-loaded content (skeleton screens)126- Use `font-display: optional` or `size-adjust` to prevent font swap shift127128---129130## CSS Architecture Decision Table131132| Codebase context | Recommended approach |133|---|---|134| Component library / design system | CSS Modules or Vanilla Extract (scoped, no runtime) |135| React app with design tokens | Tailwind CSS with `tailwind.config` tokens |136| Server-rendered content | BEM + custom properties (no runtime overhead) |137| Micro-frontend / multi-team | CSS Modules (hard scope boundaries) |138139**Design tokens are the source of truth.** Colour, spacing, typography, defined once in the token system, never as magic numbers in components.140141**Tailwind discipline:**142- Extract a component with `@apply` only when a pattern repeats 3+ times across files143- Never put `@apply` in component files, define it in a shared stylesheet or component class144- Prefer `cn()` / `clsx()` for conditional classes over inline ternaries145146---147148## Performance Checklist149150- [ ] Images: correct format (WebP/AVIF), correct size, `loading="lazy"` for below-fold, `loading="eager"` for LCP151- [ ] Code splitting: dynamic `import()` for heavy components (chart libraries, rich text editors)152- [ ] Bundle: no barrel file re-exports of entire libraries; check bundle with `vite-bundle-visualizer`153- [ ] Fonts: `font-display: swap` or `optional`; preload critical fonts154- [ ] No layout thrash: avoid reading layout properties (offsetWidth) immediately after writing styles155- [ ] `prefers-reduced-motion`: all animations/transitions respect this media query156157---158159## Testing160161- Component tests: Testing Library with accessible queries (`getByRole`, `getByLabelText`), never `getByTestId` unless nothing else works162- Test behaviour, not implementation: assert what the user sees and can interact with163- Accessibility unit testing: `@testing-library/jest-dom` + `axe-core` (`toHaveNoViolations()`)164- E2E: Playwright for critical user journeys only165166---167168## Output Protocol169170End every response with a confidence signal on its own line:171172```173CONFIDENCE: [High|Medium|Low], [one-line reason]174```175176- **High**, output is complete, correct, and based on sufficient context177- **Medium**, output is reasonable but contains an assumption or a gap; state the assumption inline178- **Low**, insufficient context to produce a reliable result; state what is missing179180If the task is outside this skill's scope or you lack the information needed to proceed, return this instead of a confidence signal:181182```183BLOCKED: [reason], [what information would unblock this]184```185186Do not guess or produce low-quality output to avoid returning BLOCKED. A precise BLOCKED is more useful than a low-confidence guess.
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