Frontend

Frontend Architecture & UX

Stack

• Next.js App Router
• React 19
• React Query (the only remote state manager)
• shadcn/ui + Tailwind CSS

Core Architecture Rules

Rendering Model

• Server Components by default
• Client Components only for interactivity
• No Client Component by convenience
• Client Components must be explicitly justified

Client Component Boundaries

Client Components must not:

• Import Server Components
• Access environment variables
• Perform direct data fetching
• Contain business or domain logic

Client Components may only:

• Handle user interaction
• Manage local UI state
• Consume hooks
• Render presentation logic

Layered Responsibilities

• UI Components

  • Pure presentation
  • No business rules
  • No data normalization

• Hooks

  • Compose UI state
  • Integrate React Query
  • No business decisions

• Domain / Services

  • Business rules
  • Decision making
  • Data validation

• API Layer

  • HTTP adaptation
  • Contract enforcement
  • Error translation

Data & State Management

• React Query is the only remote state manager
• No direct data mutations without React Query
• No fetch calls outside the API layer

React Query Rules

• Every query must have a stable queryKey
• Mutable objects are forbidden in queryKey
• All mutations must explicitly invalidate or update cache
• refetchOnWindowFocus is disabled by default
• Errors must always be handled explicitly
• Silent failures are forbidden

UX Best Practices

Accessibility

• Accessibility first
• ARIA roles where applicable
• Full keyboard navigation support
• Respect prefers-reduced-motion

Visual Consistency

• Clear visual hierarchy
• Consistent spacing and typography
• Design tokens must be respected
• Avoid layout shifts (CLS)

States Handling

Every async interaction must define:

• Loading state (prefer skeletons over spinners)
• Error state (user-friendly, not technical)
• Empty state (intentional, not accidental)

Technical errors must never be shown directly to users.

Performance Rules

• Minimize client-side JavaScript
• Memoize only when measured or clearly justified
• Defensive memoization is forbidden
• Avoid unnecessary re-renders
• Lazy-load non-critical components only
• Dynamic imports must not affect critical rendering paths

Developer Experience (DX)

• Reusable components over duplication
• Clear, explicit naming
• Prefer composition over configuration
• Avoid deep prop drilling

Props Discipline

• More than 5 props requires design reconsideration
• Boolean explosion is forbidden (isA, isB, isC)
• Prefer explicit components over conditional flags

Non-Negotiables

• No business logic in UI
• No direct backend calls from components
• No architectural shortcuts
• Predictability over flexibility

Architectural violations are treated as bugs.