dev-frontend

Dev-Frontend — Domain-Correct Frontend Engineering

Build distinctive, production-grade interfaces that fit the product domain, locale, interaction model, and real visual evidence.

This skill has modular references for specialized guidance — read the relevant ones before coding.

It activates by change surface whenever the work is primarily frontend, UI, styling, responsive layout, or animation.

> Role separation: For design judgment — typography/color/layout direction, UX decision

> gates, product personalities, or vague visual briefs — load dev-uiux-design first. This

> skill implements the chosen direction; dev-uiux-design makes the design decisions.

> Implementation anti-slop enforcement stays here; design taste/pattern judgment lives there.

> C0/C1 work (small local patches): See dev §0.0 Work Classifier + §0.1 Patch Fast-Path before reading references.

Modular References

Start with anti-slop.md, aesthetics.md, responsive-viewport.md, and visual-verification.md. Add domain/locale/stack references only when relevant.

For C2 ordinary app screens (form/table/list/detail), crud-ui.md alone suffices; add the style references above for marketing/visual surfaces or C3+ work.

When frontend choices depend on current framework, design-system, browser API,

library behavior, browser-rendered source evidence, or package/source freshness,

read the active search skill and follow its source-fetch and evidence-status

rules before treating external material as proof.

Verification grounding

STRICT: For render/executable artifacts (HTML, SVG, games, UI, charts),

run the real renderer: headless browser, screenshot, canvas check, or equivalent.

Observe the actual output yourself, fix what observation reveals, then re-run.

Static parsing confirms well-formed files; it does not prove the artifact is

visually or interactively correct. One clean observation is enough for unchanged

state; do not re-render unchanged output just to repeat evidence.

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0. Frontend Routing

Before designing or coding, classify the work:

Default rules:

• For apps/tools/dashboards, build the actual working surface first, not a marketing hero.
• For Korean-first work, read korea-2026.md and ux-writing-ko.md.
• For any soft 3D miniature, mascot, chibi, toy-like object, or character-like asset, read soft-3d-asset-gates.md.
• For product/brand/object/place/person pages, use concrete visual assets in the first viewport.
• For finance, government, B2B, admin, auth, security, and developer tools, keep visual warmth restrained and subordinate to clarity.
• Every user-facing decision point must justify its existence — defaults first, one primary action per screen, choices demoted to progressive disclosure; surface-conditional per density profile (dev-uiux-design UX-LAZY-01 owns the gate).
• For text-heavy surfaces (landing, marketing, editorial, public service), apply typography wrapping defaults — see typography-wrapping.md. Dashboard table cells are excluded.

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1. Component Identification

When the user describes UI in vague terms (e.g. "접히는 거", "팝업 같은 거"):

1. Recommend the best-fit component with reasoning: <Name> — <what it does, why it fits>
2. Confirm, then proceed

If the user already names a specific component, skip this step.

Reference: component.gallery/components

For new React/Vue/Svelte/Next UI source files, prefer .tsx or typed component files when the repo supports TypeScript. Inherit dev TypeScript strict-compatibility rules.

If frontend structure is unclear, read existing source-of-truth docs/logs first, then document pages, components, routes, state stores, and build commands in the repo's existing SOT before broad implementation.

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1.5 Objective Gates vs Style Samples

Two different kinds of rules live in this skill (see dev §0.2):

• Objective UX gates (STRICT/DEFAULT) — accessibility baseline (§7, §11), state coverage

(loading/empty/error/permission), keyboard operability, visible focus, contrast. Missing

these are review findings.

• Style direction (STYLE_SAMPLE) — design thinking (§2), aesthetics, density profiles,

product personalities, preset tokens, and the concrete values in §4-§5 (palettes, font

choices, pixel max-widths). These illustrate acceptable choices; they are NOT

requirements, must not override an existing design system (Design System Detection stays

MANDATORY), and must never be enforced as universal taste (UX-STYLE-01).

2. Design Thinking

Before coding, commit to a domain-correct direction:

• Purpose: What problem does this interface solve? Who uses it?
• Surface: Is this a working tool, dashboard, public service, AI workflow, game, landing page, or editorial surface?
• Tone: Pick a specific direction. For product tools this often means quiet, dense, trustworthy, and fast rather than loud.
• Constraints: Framework, performance budget, accessibility requirements.
• Signature: What ONE thing will make this unforgettable?

When user intent is vague ("깔끔하게", "모던하게", "just make it look good"), read the dev-uiux-design skill and run the User Intent Discovery Protocol before making routing decisions.

If the user cannot answer these questions, use the dev-uiux-design skill's structured preference elicitation flow. Offer product references ("Notion 느낌? Linear 느낌?") and visual comparisons.

Intentionality over intensity. Bold maximalism, refined minimalism, dense utility, and friendly consumer UI can all work when they match the domain.

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3. Baseline Configuration

Adjust these dials based on what's being built. Present to user if unclear.

After Design Read, set dials per dev-uiux-design §2 Dial Setting.

Product density profile (D1-D8 in references/core/product-density.md) sets component class; VISUAL_DENSITY (1-10) sets spacing within that class. These are orthogonal axes.

Adapt dynamically based on user requests. Dashboard → density up. Portfolio → variance up. Data tool → motion down.

Korean app/tool surfaces usually need higher density and clearer hierarchy, not oversized hero text.

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4. Implementation

Read references/core/aesthetics.md for full guidelines. Summary:

• Typography: Use domain-appropriate typography. For Korean-first UIs, prioritize CJK-safe stacks before Latin display fonts. Apply text-wrap: balance on all headings AND short descriptors (hero subtitle, card description, caption — anything 1-3 lines). Use text-wrap: pretty only on body paragraphs (4+ lines). pretty has no effect on short text and will leave Korean orphans like "합니다." or "화." on a line alone. See typography-wrapping.md for full rules.
• Color: Max 1 accent. Use neutral bases (Zinc/Slate) with singular high-contrast accent — avoid purple-on-white.
• Layout: Match the product surface. Avoid centered-card/hero patterns in repeated-use tools.
• Motion: See references/core/motion.md. One well-choreographed page load > 10 scattered effects.
• Assets: Use screenshots, product images, diagrams, charts, illustrations, generated bitmaps, or soft 3D only when they add product meaning.

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5. Anti-Slop Enforcement

Rule classes (dev §0.2): items below are DEFAULT — deviate with a stated reason; concrete

values and palettes are STYLE_SAMPLE (§1.5); the emoji-as-UI-icon ban is the only STRICT item.

Read references/core/anti-slop.md for full rules. Key standards:

• Treat unexamined default typography as a slop signal. Choose a domain-appropriate stack; Korean-first UI should use CJK-safe fonts and system fallbacks deliberately.
• Gradient overuse is the #1 AI tell (2026) — audit gradients first. Budget: max 1 ambient gradient per viewport; gradients on 3+ sibling cards is gradient soup — see anti-slop.md § Gradient Budget
• One-note theme ban: full-page single-hue washes (terminal green, cyber cyan, CRT amber) are the dark-mode purple-on-white — neutral dark base + accent on <10% of surface. See anti-slop.md § One-Note Theme Ban
• Use neutral or intentional color palettes — purple gradients on white remain the legacy tell
• No self-describing meta copy: UI text must sell the product, never narrate the mockup, layout, or responsive behavior ("벤토 보드", "다른 배율로 재사용", viewport pill rows) — see anti-slop.md § Self-Describing Meta Copy
• Use asymmetric or purposeful layouts — centered-everything reads as template
• Vary card sizes, spans, and groupings — equal 3-card grids read as generic
• Bento grids must compose as one interlocking slab: aligned row edges, 1 dominant cell, span tracks content weight, no orphan tail — see layout-discipline.md § Bento Composition
• Never reuse the same image twice on one page (hero + crop/zoom tile) — each slot earns distinct content
• Avoid oversized bold hero text inside tools, dashboards, admin, finance flows, and public services
• Hero composition: the split hero (left bold headline + right boxed screenshot/mockup card) is demoted to paid-conversion LPs; on brand/product homepages the product visual is the stage (full-width, background, or interactive demo), never a right-column card — see layout-discipline.md § Hero Composition Grammar
• Avoid asset-free UI: abstract blobs/gradients do not replace real visual evidence
• Avoid generic soft 3D icon packs; soft 3D must be semantic, brand-consistent, and restrained
• NEVER use emoji as UI visual elements (feature icons, card icons, section markers, buttons) — emoji in production UI is the #1 AI slop signal. Use SVG icons (Lucide/Phosphor/Heroicons). See anti-slop.md § Emoji Slop
• Warm beige/cream backgrounds with brass/clay accents are banned as defaults for premium-consumer briefs — see anti-slop.md § Premium-Consumer Palette Ban
• Layout monotony (same family repeated, 3+ zigzag sections, overused eyebrows) — see references/core/layout-discipline.md
• Color, shape, and theme must be locked per-page and audited before shipping — see references/core/consistency-locks.md
• Use off-black (#0a0a0a, #111) — pure #000000 lacks depth
• Responsive enforcement: every multi-column section must declare its mobile/tablet collapse behavior — "it'll work at mobile" is not a plan. See responsive-viewport.md
• Page containment required: max-w-[1400px] mx-auto or equivalent wrapper. Content stretching to viewport edges on wide monitors is a layout bug
• Mobile is a different product: section composition, CTA placement, and interaction model change on mobile — it is NOT just "desktop stacked vertically." See mobile-ux.md
• Use realistic, specific names and brands in placeholder content
• Write original copy — avoid "Elevate", "Seamless", "Next-Gen" and similar clichés
• Treat uncontrolled heading line breaks (orphaned single word, no text-wrap, no max-width in ch) as a slop signal — see typography-wrapping.md
• Treat short descriptors (hero subtitle, card description, caption) using text-wrap: pretty instead of balance as a slop signal — pretty does nothing on 1-3 line text, especially Korean
• Treat Korean orphan fragments ("합니다.", "화.", "입니다." alone on a line) as a slop signal — always verify Korean text breaks at target viewports
• Treat generic stroke icons as brand logo substitutes as a slop signal — use actual brand SVGs from Simple Icons, SVGL, or press kits. See brand-asset-sourcing.md

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6. Performance Guardrails

• Animate transform and opacity only — layout properties cause jank
• Grain/noise filters → fixed pseudo-elements only, off scrolling containers
• will-change sparingly (remove after animation); z-index only for systemic layers
• Memoize perpetual animations in isolated components
• Browser connection budgets (≤2 SSE/WS per origin per page, multiplex over

multiplying, no per-component polling): detail + limits table in

references/core/performance-budget.md (this skill owns browser-side budgets;

server connection lifecycle is owned by dev-backend §1)

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7. Accessibility Baseline

• Semantic HTML (<button>, <nav>, <main>); keyboard navigation for all interactive elements
• WCAG AA minimum (4.5:1 normal text, 3:1 large text); visible focus indicators; prefers-reduced-motion
• Skip link; focus never hidden by sticky headers/bars/sheets/overlays
• Icon-only buttons need accessible names; charts/status/loading/AI-streaming states need labels or live regions
• Do not encode meaning by color alone
• Modals, menus, comboboxes, bottom sheets, command palettes: complete keyboard path —

trap focus, restore on close, Escape; arrow-key navigation; honest aria-expanded/

aria-haspopup/aria-activedescendant; tab order follows visual flow

• Stress-test Korean long labels and screen-reader names; clipped Hangul is a failure
• Pointer targets follow WCAG 2.2 AA target-size (24×24 CSS px minimum with exceptions);

44×44px is a conservative product baseline, not the legal minimum

• Test with screen reader and keyboard-only navigation; deep patterns → a11y-patterns.md

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8. React Behavior Rules (hooks · performance · forms)

Full guidance moved to references/stacks/react.md § Behavior Rules. Router decisions:

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12. 2026 Frontend Platform Rules (verified 2026-07-02)

Use this section when modernizing or creating React/Next/Vite frontends. Prefer project

conventions first. Version-detail depth lives in references/stacks/react.md / nextjs.md.

React (19.2.x line)

• <Activity> (stable): state-preserving hidden UI (tabs, drawers, route shells) — not for security hiding or active subscriptions.
• useEffectEvent: non-reactive Effect logic needing latest props/state; never call during render or pass to children.
• Partial Pre-rendering: static shell + explicit dynamic holes + Suspense; nothing request-specific in the shell.
• React Compiler (stable, optional): measure before memoizing (§8).
• Performance gate: inspect React Performance Tracks in Chrome DevTools before adding memoization or blaming rendering.

Next.js (16.x)

• Turbopack is the default bundler (webpack is opt-in --webpack).
• Cache Components (cacheComponents: true): dynamic by default; cache only explicit use cache + cacheLife + cacheTag; PPR is expressed through Cache Components (the old experimental.ppr flag is gone).
• Never cache user/session data without a user-scoped cache key.
• Server Actions: validate server-side, authorize against the resource, revalidate affected tags.

Modern CSS (Baseline check before shipping)

Prefer native CSS before JS layout observers/animation libraries: container queries,

:has(), subgrid (all Baseline widely-available), View Transitions (same-document,

Baseline 2025 newly-available — provide fallback for cautious audiences),

text-wrap: balance/pretty, dvh/svh/lvh units, logical properties, shallow CSS

nesting. Tailwind v4 (CSS-first config, theme variables). Record Baseline status

(widely/newly/caution) for each modern feature used and decide fallback per audience.

Build Tools

• Vite 8: Rolldown/Oxc is the integrated default bundler (rolldown-vite is only a

Vite 7 migration bridge). Node 20.19+/22.12+; Baseline target Chrome/Edge 111,

Firefox 114, Safari 16.4.

• Detect Vite 7 vs 8 before editing config — don't assume Rollup/esbuild-era plugins.
• Do not introduce Webpack-era config unless the app is already Webpack-bound.

Agent-visible runtime diagnostics (DEFAULT)

Prefer dev servers that surface browser/runtime errors to the CLI/agent before relying

on static review: Vite 8 forwards browser console to the dev server (auto-activates for

coding agents); Next 16 ships DevTools MCP. Wire these before debugging rendered behavior.

State Classification

Before adding state, classify it:

Rules: Do not store derived state just to sync with Effect. Do not put server state in Zustand. Do not put URL-shareable state only in component state. Keep optimistic state reversible.

Design System Detection (MANDATORY — before creating tokens)

Before inventing design tokens, check:

1. Does the project have an installed design system? (grep -r "material-ui\|@mui\|carbon-components\|@carbon\|@fluentui\|govuk-frontend\|uswds" package.json)
2. Does the project have existing tokens? (find . -name "tokens.*" -o -name "theme.*" -o -name "design-system*")
3. Does the brief name a specific design system?

If YES to any: use the official package. Do not recreate CSS by hand.

If NO: proceed with dev-uiux-design/references/design-system-bootstrap.md.

shadcn/ui and AI-Assisted UI

• Inspect existing installed components before adding new ones
• Use project's components.json, aliases, tokens, and registry conventions
• Do not hallucinate design-system components; verify against local source
• Remove demo-only copy and unused variants

For AI-native interfaces (chat, agent, copilot), design explicit states: empty → prompt ready → submitted → streaming → tool call → result → complete → feedback. Never fake streaming, citations, or tool calls.

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13. Error Boundaries

Wrap each major section (not the whole app); boundary renders friendly message + retry +

report link; log to monitoring in componentDidCatch; never show stack traces to users.

Error hierarchy: field-inline → form-summary → section Error Boundary → page error.tsx

→ root boundary (offline/crash page).

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14. Pre-Flight Gates

Gates apply to production surfaces (dev §0.4 shared definition); prototypes and

internal demos are exempt unless production polish is requested.

Full ~40-item checklist: references/core/preflight-full.md — run it for launches

and audits. The blocking gates below are the minimum for every production delivery:

• [ ] Design Read declared before code (dev-uiux-design §2); surface/locale/density/asset/motion classified (§0)
• [ ] Anti-slop enforced (§5) — incl. emoji-as-icon ban (STRICT)
• [ ] Loading, empty, and error states provided
• [ ] Accessibility baseline (§7): keyboard path, focus management, contrast, reduced motion
• [ ] Mobile collapse per section type + touch targets ≥44px + min-h-[100dvh] + page containment
• [ ] State classified before adding store/Context/Effect/cache (§12 table)
• [ ] Forms: schema validation + field-level errors (§8)
• [ ] Korean-first UI: CJK typography + word-break: keep-all + orphan screenshot check
• [ ] AI UI states honest: no fake streaming, citations, or tool calls
• [ ] Core Web Vitals are the performance gate (INP ≤200ms field data); Lighthouse

Performance score is an advisory smoke signal, not the blocker — budgets in performance-budget.md

• [ ] Rendered verification run (§ Verification grounding): screenshots at mobile/tablet/desktop
• [ ] Error Boundaries wrap major sections (§13); stack-specific rules followed (references/stacks/)

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15. Backend Contract & Security Alignment

Playwright smoke validates rendered flows AFTER API + contract tests pass; frontend unit

tests mock the same envelope shape as dev-backend §5; error-code changes update

frontend error-mapping tests.