build

name	build
description	Build frontend components from design prototypes. Triggers on: "build from design", "implement this design", "prototype to code", "design to frontend", "implement this UI", "turn this design into code", "code this mockup".
allowed-tools	Read, Write, Edit, Glob, Grep, Bash, AskUserQuestion, Agent

Frontend Craft — Design to Components

Transform design prototypes into maintainable, component-based frontend code through structured analysis and incremental generation.

Core Principles

1. Components, not pages — Always generate one component at a time. Never produce an entire page in a single pass.
2. Tokens, not values — Every visual property (color, spacing, font size) must reference a design token. No hardcoded hex codes, pixel values, or magic numbers.
3. Libraries first — Use existing component library primitives (shadcn/ui, Radix, Element Plus, etc.) before building custom implementations. Do not reimplement datepickers, modals, tables, or select menus.
4. Match conventions — In existing projects, mirror the established code style, naming, directory structure, and patterns exactly.
5. Confirm before code — The architecture plan (Phase 2) must be confirmed by the user before any code is written.

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Phase 0: Input Validation

Required Inputs

1. Design prototype — image file path (PNG, JPG, WebP), PDF path, or screenshot
2. Tech stack — framework + styling + component library

Procedure

1. Verify the design file exists and is readable. Use the Read tool for images and PDFs.
2. If the user did not specify a tech stack, ask with AskUserQuestion:
   • Framework: React / Next.js, Vue 3 / Nuxt, Svelte / SvelteKit, Other
   • Styling: Tailwind CSS, CSS Modules, styled-components / CSS-in-JS, UnoCSS, Other
   • Component library (optional): shadcn/ui, Radix UI, Headless UI, Element Plus, Naive UI, None
3. Detect whether this is an existing project or a new one:
   • Scan for package.json, tsconfig.json, vite.config.*, next.config.*, nuxt.config.*, svelte.config.*
   • Existing project: scan code conventions before proceeding:
     • Naming conventions (file names, component names, variable names)
     • Directory structure (where components, pages, styles live)
     • Already-used component libraries and utilities
     • State management approach (useState, Zustand, Pinia, Svelte stores, etc.)
     • Styling approach in use
   • New project: note that scaffolding is needed in Phase 3

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Phase 1: Design Analysis

Read the design prototype using the Read tool. Produce a structured analysis covering:

1.1 Visual Hierarchy

Identify top-level layout regions: header, navigation, sidebar, main content, footer, overlays. Note their spatial relationships and nesting.

1.2 Color System

Extract colors and classify them:

Role	Example	Usage
Primary	#3B82F6	CTAs, active states, links
Secondary	#6366F1	Supporting accents
Accent	#F59E0B	Highlights, badges
Neutral	#1F2937, #F3F4F6	Text, backgrounds, borders
Semantic	#EF4444, #22C55E	Error, success states

Refer to DESIGN-ANALYSIS.md for extraction methodology.

1.3 Typography System

Identify font hierarchy:

Level	Properties
Heading 1	font-family, size, weight, line-height
Heading 2	...
Body	...
Caption / Small	...

1.4 Spacing System

Infer the base spacing unit and common patterns. Look for the smallest repeated gap and derive the scale (e.g., 4px base: 4, 8, 12, 16, 24, 32, 48, 64).

1.5 Interactive Elements

Catalog all interactive elements: buttons (variants, sizes), inputs, selects, toggles, checkboxes, links, tabs, modals, dropdowns.

1.6 Responsive Clues

If the design includes multiple viewport sizes, note breakpoint behavior. If only one size is provided, infer a reasonable responsive strategy.

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Phase 2: Architecture Planning

This phase requires user confirmation before proceeding to code.

2.1 Component Tree Decomposition

Apply Atomic Design principles. Refer to COMPONENT-ARCHITECTURE.md for methodology.

Break the design into:

• Atoms: Smallest indivisible UI elements (Button, Input, Badge, Avatar, Icon)
• Molecules: Combinations of atoms (SearchBar, FormField, NavLink, Card)
• Organisms: Complex sections composed of molecules (Header, Sidebar, ProductGrid, CommentSection)
• Templates: Page-level layouts that arrange organisms
• Pages: Templates populated with real content and data

For each component, define:

• Name
• Responsibility (one sentence)
• Props interface draft (key props, types, defaults)
• State requirements (local state, context, global store)
• Children / composition pattern

2.2 Design Tokens

Map the Phase 1 analysis to the tech stack's token format:

Tech Stack	Token Format
Tailwind CSS	tailwind.config.ts — extend theme
CSS Modules / vanilla	CSS custom properties in variables.css
styled-components	Theme object in theme.ts
UnoCSS	uno.config.ts — extend theme

Tokens must cover: colors, spacing scale, typography scale, border radii, shadows, breakpoints.

2.3 File Structure Plan

Propose the directory layout for new components, following existing project conventions (or sensible defaults for new projects).

2.4 Reusable Library Components

Identify which components from the chosen component library can be used directly or composed, avoiding custom reimplementation.

2.5 State Management Plan

Based on complexity, recommend:

Complexity	Approach
Simple (single component state)	Local state (useState, ref, $state)
Shared across siblings	Lift state / Context / provide-inject
App-wide or complex	Zustand, Pinia, Svelte stores

2.6 User Confirmation Gate

Present the full architecture plan to the user via AskUserQuestion:

• Component tree (names and hierarchy)
• Design tokens summary
• File structure
• Library components to use
• State management approach

Options: Approve / Approve with changes / Revise

Do not write any code until the user approves.

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Phase 3: Foundation Setup

New Project

1. Scaffold using the appropriate CLI tool via Bash:
   • npx create-next-app@latest / npm create vite@latest / npx nuxi init / npm create svelte@latest
2. Install styling dependencies (Tailwind, etc.)
3. Install chosen component library

Existing or New Project

1. Generate design tokens configuration file:
   • Tailwind: extend tailwind.config.ts
   • CSS variables: create or update globals.css / variables.css
   • Theme object: create theme.ts
2. Generate base layout component(s) — the outermost shell (e.g., root layout with header/sidebar/main slots)
3. Install additional dependencies as needed via Bash

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Phase 4: Component Generation

This is the core phase. Generate components one at a time, in dependency order.

Generation Order

1. Atoms (no dependencies on other custom components)
2. Molecules (depend on atoms)
3. Organisms (depend on molecules and atoms)

Per-Component Rules

For each component:

1. Follow project conventions — match existing naming, file structure, export patterns
2. Use design tokens — every color, spacing, font-size, border-radius, shadow must come from tokens. No hardcoded values.
3. Prefer library components — use the chosen component library's primitives where applicable
4. Responsive handling — include at minimum mobile + desktop breakpoints
5. TypeScript types — if the project uses TypeScript, define a props interface
6. File size limit — if a component exceeds ~100 lines, extract sub-components
7. Accessibility baseline — semantic HTML, aria labels for non-obvious elements, keyboard focusability for interactive elements

Refer to CODE-GENERATION.md for tech-stack-specific conventions.

Generation Pattern

For each component:

1. Create the component file
2. Define the props interface (TS projects)
3. Implement the component using design tokens and library primitives
4. Add responsive styles
5. Export the component

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Phase 5: Page Assembly

Once all components are generated:

1. Compose the page — import and arrange organisms within the template/layout
2. Add data fetching — if the design implies dynamic content, add data fetching logic appropriate to the framework (Server Components, getServerSideProps, useFetch, load functions)
3. Add routing — configure routes if the page needs to be accessible via URL
4. Wire up interactions — connect state, event handlers, and any cross-component communication

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Phase 6: Quality Review

Run through the checklist in QUALITY-CHECKLIST.md.

Key checks:

• All colors reference design tokens
• All spacing values reference the spacing scale
• No inline magic numbers
• TypeScript interfaces defined for all component props (TS projects)
• Interactive elements have hover, focus, and active states
• Semantic HTML tags used appropriately
• Basic keyboard navigation works for interactive elements
• Responsive styles cover at least mobile + desktop
• No unused imports
• No component file exceeds 200 lines

Deliverables

After completing the review, provide:

1. Summary of generated components (name, file path, line count)
2. Design token configuration location
3. Remaining items that require follow-up:
   • Real API endpoints to connect
   • Additional interaction states to implement
   • Missing assets (icons, images) to replace placeholders
   • Animations or transitions not covered

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Reference Documents

• DESIGN-ANALYSIS.md — How to extract visual systems from design prototypes
• COMPONENT-ARCHITECTURE.md — Component decomposition and props design methodology
• CODE-GENERATION.md — Tech-stack-specific code conventions and patterns
• QUALITY-CHECKLIST.md — Complete quality verification checklist