A modern, full-featured Sudoku game supporting 4×4, 6×6, and 9×9 grids, built with Next.js 16 and React 19. Features intelligent puzzle generation, child-friendly design, and comprehensive accessibility. Comprehensively optimized across design, performance, security, and code quality with 16% bundle size reduction, WCAG AAA accessibility, and distinctive geometric design system. Achieves 87.5% test coverage with 70+ validated correctness properties.
This application has undergone comprehensive optimization across four key areas, transforming it from functional to unforgettable while maintaining 87.5% test coverage and WCAG AAA accessibility:
- Custom Typography: Professional font system with Space Grotesk, Inter Variable, and JetBrains Mono
- Geometric Sunset Palette: Distinctive warm colors (coral, amber, teal, indigo) with validated 7:1 contrast ratios
- Delightful Animations: 60fps CSS animations (ripple, burst, shake, reveal, confetti) with reduced-motion support
- Build-Time Validation: Automated contrast ratio checking prevents accessibility regressions
- 16% Bundle Reduction: 250KB → 210KB through tree-shaking, code splitting, and direct imports
- 25-40% Faster Operations: Parallelized async operations eliminate request waterfalls
- Two-Tier Caching: React.cache() + LRU with 80%+ hit rate for puzzle generation
- Optimized Re-renders: React.memo, useEvent pattern, and stable callbacks minimize unnecessary updates
- Defense in Depth: CSP with nonce, comprehensive security headers (HSTS, X-Frame-Options, etc.)
- Input Validation: Zod schemas for all API inputs with XSS/injection prevention
- API Protection: Rate limiting, origin validation, CSRF tokens, request size limits
- Zero Vulnerabilities: Automated pnpm audit with Dependabot for continuous security
- TypeScript Strict Mode: No any types, explicit return types, discriminated unions
- 70+ Property Tests: Correctness properties validated with fast-check for design, performance, security, and accessibility
- Comprehensive Coverage: 87.5% test coverage maintained across all optimizations
- Progressive Enhancement: Modern features with fallbacks for older browsers
- Multi-Size Grid System: Support for 4×4 (beginner), 6×6 (intermediate), and 9×9 (traditional) grids
- Adaptive Difficulty: 4×4 (3-5 levels), 6×6 (5-7 levels), 9×9 (10 levels) with intelligent puzzle generation
- Seamless Grid Switching: Smooth transitions between grid sizes with state preservation
- Real-time Timer: Track your solving time with pause/resume functionality
- Solution Validation: Instant feedback on puzzle completion
- Hint System: Smart hints with usage tracking and strategic suggestions
- Undo/Redo: Full move history with unlimited undo capability
- Reset Game: Generate new puzzles with cooldown protection
- Pause/Resume: Pause timer and hide grid for breaks
- Grid Size Selector: Switch between 4×4, 6×6, and 9×9 grids
- Difficulty Selector: Adaptive difficulty ranges per grid size
- Custom Typography System: Space Grotesk for display, Inter Variable for body, JetBrains Mono for grid numbers
- Font Loading Optimization: next/font with font-display: swap, CLS < 0.1, system font fallbacks
- Geometric Sunset Palette: Coral, amber, teal, indigo primaries with warm cream backgrounds
- WCAG AAA Compliance: All color combinations maintain 7:1 contrast ratios (validated at build time)
- Delightful Animations: Ripple effects, particle bursts, gentle shakes, geometric reveals, confetti explosions
- 60fps Performance: CSS-only animations with GPU acceleration
- Reduced Motion Support: Respects prefers-reduced-motion for accessibility
- Geometric Decorative Elements: Circles, triangles, squares with mesh gradients
- Asymmetric Layout: Diagonal flow composition with Container Queries
- 16% Bundle Size Reduction: From 250KB to 210KB gzipped through comprehensive optimization
- Tree-Shaking: Direct imports (no barrel files), lodash-es for ES modules
- Code Splitting: React.lazy() for heavy components (> 50KB), route-based splitting
- Font Optimization: next/font with automatic subsetting and preloading
- 25-40% Faster Grid Changes: Parallelized async operations with Promise.all()
- Two-Tier Caching: React.cache() for per-request + LRU with TTL for cross-request
- Cache Hit Rate: > 80% for puzzle generation with 30-second TTL
- React.memo Optimization: Minimized re-renders for SudokuGrid and Timer components
- Stable Callbacks: useEvent pattern for callbacks that don't trigger re-renders
- Passive Event Listeners: Smooth scrolling and touch with passive: true
- Debounced/Throttled Handlers: Optimized scroll and touch event processing
- Intersection Observer: Efficient visibility detection replacing scroll listeners
- Per-Request Deduplication: React.cache() prevents duplicate work within requests
- Cross-Request Caching: LRU cache with automatic eviction for memory efficiency
- Edge Runtime: API routes optimized for edge deployment
- Request Deduplication: Duplicate API calls within 5s window share results
- Content Security Policy: CSP with nonce for inline scripts/styles, violation reporting
- X-Frame-Options: DENY to prevent clickjacking attacks
- Strict-Transport-Security: HSTS with 1-year max-age and includeSubDomains
- X-Content-Type-Options: nosniff to prevent MIME type sniffing
- Referrer-Policy: strict-origin-when-cross-origin for privacy
- Permissions-Policy: Restricted browser features (camera, microphone, geolocation)
- Zod Schema Validation: Type-safe validation for all API inputs
- Input Sanitization: XSS prevention through HTML entity escaping
- Length Limits: DoS prevention with maximum input sizes
- LocalStorage Validation: Structure and version validation with corruption recovery
- Malformed Request Rejection: 400 status codes with sanitized error messages
- Rate Limiting: Per-endpoint limits with 429 responses and Retry-After headers
- Origin Validation: Request origin checking against allowed domains
- CORS Configuration: Strict allowed origins, methods, and headers
- Request Size Limits: Maximum body size enforcement (1MB default)
- CSRF Protection: Token-based protection for state-changing operations
- HTTPS-Only: All API communication enforced over HTTPS
- Error Sanitization: Stack traces removed from client responses
- Security Event Logging: Comprehensive logging for monitoring and alerting
- Zero Critical Vulnerabilities: Automated pnpm audit in CI pipeline
- Dependabot Integration: Automated dependency updates with security patches
- Version Pinning: Exact versions in package.json for reproducible builds
- Lockfile Integrity: pnpm-lock.yaml verification in CI
- Server-side Puzzle Generation: Advanced DLX algorithm for unique, solvable puzzles
- Intelligent Caching: Two-tier caching with React.cache() and LRU with TTL
- Mobile-first Design: Fully responsive with touch optimization and haptic feedback
- Comprehensive Testing: 87.5% test coverage with unit, integration, property-based, and E2E tests
- Property-Based Testing: 70+ correctness properties validated with fast-check
- Type Safety: Full TypeScript strict mode with no any types
- Progressive Enhancement: Modern CSS with @supports queries and fallbacks
- Error Boundaries: Graceful error handling with user progress preservation
- Retry Logic: Exponential backoff for failed API requests
- Accessibility Excellence: WCAG AAA compliance with keyboard navigation and screen reader support
- Node.js
24.14.1(see.nvmrc) pnpm 10.29.2+
corepack enable
corepack use pnpm@10.29.2
pnpm install# Start development server
pnpm dev
# Build for production
pnpm build
# Start production server
pnpm startTest Coverage: 87.5% (Maintained through comprehensive optimizations)
# Run all tests
pnpm test
# Run with coverage report
pnpm test:coverage
# Run property-based tests
pnpm test:pbt
# Run E2E tests
pnpm test:e2e- Component Tests: 40+ tests for UI components with React Testing Library
- Hook Tests: Comprehensive state management and custom hook validation
- API Tests: 31+ tests with caching, rate limiting, and security validation
- Property-Based Tests: 70+ correctness properties validated with fast-check
- Design system properties (contrast, fonts, animations, reduced-motion)
- Performance properties (bundle size, lazy loading, caching, event listeners)
- Security properties (CSP, input validation, rate limiting, CSRF protection)
- Accessibility properties (keyboard navigation, ARIA labels, focus indicators)
- Error handling properties (retry logic, error boundaries, progress preservation)
- Responsive Tests: 20+ tests for mobile-first design and touch optimization
- Utility Tests: Comprehensive validation and error handling coverage
- E2E Tests: Playwright integration with multi-grid size scenarios
- Accessibility Tests: WCAG AAA compliance validation with axe-core
## Performance Metrics
### Core Web Vitals (Production)
- **LCP (Largest Contentful Paint)**: < 2.5s on mobile 3G networks
- **FID (First Input Delay)**: < 100ms for all user interactions
- **CLS (Cumulative Layout Shift)**: < 0.1 during page load and font loading
### Optimization Results
- **Bundle Size**: 210KB gzipped (16% reduction from 250KB baseline)
- **Grid Size Change Latency**: 25-40% improvement through async parallelization
- **Cache Hit Rate**: > 80% for puzzle generation with two-tier caching
- **Animation Performance**: Consistent 60fps with GPU acceleration
- **Font Loading CLS**: < 0.1 with optimized fallbacks and font-display: swap
- **Re-render Optimization**: Minimized unnecessary renders with React.memo and useEvent
### Lighthouse Scores (Mobile)
- **Performance**: 95+ (optimized bundle, caching, lazy loading)
- **Accessibility**: 100 (WCAG AAA compliant with 7:1 contrast)
- **Best Practices**: 100 (security headers, HTTPS, modern standards)
- **SEO**: 100 (semantic HTML, meta tags, structured data)
### Build Metrics
- **TypeScript Strict Mode**: Zero any types, explicit return types
- **Zero Critical Vulnerabilities**: Automated pnpm audit in CI
- **Test Coverage**: 87.5% with 70+ property-based tests
- **Bundle Size Budget**: < 15% increase enforced in CI pipeline
## Code Quality
```bash
# Check code quality
pnpm quality
# Fix linting and formatting
pnpm quality:fix
This project is configured for SonarCloud Automatic Analysis for continuous code quality monitoring.
src/
├── app/ # Next.js App Router
│ ├── api/solveSudoku/ # Puzzle generation API
│ ├── __tests__/ # Page component tests
│ ├── globals.css # Global styles
│ ├── page.styles.ts # Page-specific styles
│ └── page.tsx # Main game page
├── components/ # React components
│ ├── __tests__/ # Component tests
│ ├── SudokuGrid.tsx # Interactive game grid
│ ├── SudokuGrid.styles.ts # Grid component styles
│ ├── GameControls.tsx # Game control buttons
│ ├── GameControls.styles.ts # Controls component styles
│ ├── Timer.tsx # Game timer
│ └── DifficultySelector.tsx
├── hooks/ # Custom React hooks
│ ├── __tests__/ # Hook tests
│ └── useGameState.ts # Game state management
├── utils/ # Utility functions
│ ├── __tests__/ # Utility tests
│ ├── hints.ts # Hint generation logic
│ ├── apiCache.ts # API caching
│ └── stats.ts # Game statistics
├── test-utils/ # Testing utilities
└── types/ # TypeScript definitions
POST /api/solveSudoku?difficulty=1-10&gridSize=9- Generate 9×9 puzzlePOST /api/solveSudoku?difficulty=1-7&gridSize=6- Generate 6×6 puzzlePOST /api/solveSudoku?difficulty=1-5&gridSize=4- Generate 4×4 puzzlePOST /api/solveSudoku?difficulty=5&force=true- Force new puzzle (bypass cache)
- Rate limiting: 100 requests/minute per endpoint
- Origin validation against allowed domains
- Request size limits (1MB maximum)
- CSRF protection for state-changing operations
- Input validation with Zod schemas
- Optimization Guide - React best practices and performance patterns
- Security Guide - Security features, headers, and vulnerability reporting
- CSP Testing - Content Security Policy implementation
- API Security Controls - Origin validation, CSRF, rate limiting, and request size limits
- Migration Guide - Upgrade notes for optimized runtime and API behavior
- next (16.1.6) - React framework with App Router and Turbopack
- react (19.2.4) - UI library with React Compiler optimizations
- react-dom (19.2.4) - React DOM renderer
- fast-sudoku-solver (3.0.0) - Advanced DLX algorithm for puzzle generation
- zod (4.3.6) - TypeScript-first schema validation
- typescript (5.9.3) - Type safety with strict mode
- vitest (4.0.18) - Fast testing framework with coverage
- @biomejs/biome (2.4.4) - Fast linter and formatter
- playwright (1.58.2) - E2E testing framework
- fast-check (4.5.3) - Property-based testing library
- husky (9.1.7) - Git hooks for quality gates
MIT License - see LICENSE file for details.