# GlyphDiff.com - Font Comparison Project Plan

> **Status:** Learning-Focused MVP | **Tech Stack:** SvelteKit + TypeScript + Tailwind CSS | **Transition Path:** React → Svelte

---

## Table of Contents

1. [Project Overview](#project-overview)
2. [Executive Summary](#executive-summary)
3. [Architecture Decisions](#architecture-decisions)
4. [Font Provider Integration Strategy](#font-provider-integration-strategy)
5. [Performance Optimization](#performance-optimization)
6. [Frontend Architecture](#frontend-architecture)
7. [Data Models](#data-models)
8. [Implementation Roadmap](#implementation-roadmap)
9. [TanStack Query Research](#tanstack-query-research)
10. [Learning Guide: React → Svelte](#learning-guide-react--svelte)
11. [Scalability & Commercialization](#scalability--commercialization)
12. [Deployment](#deployment)
13. [Risk Assessment](#risk-assessment)
14. [Success Metrics](#success-metrics)
15. [Appendix](#appendix)

---

## Project Overview

### Vision

Create a modern, fast, and intuitive web application for comparing fonts side-by-side. The tool will help designers, developers, and typographers make informed decisions about font choices by providing real-time visual comparisons, filtering, and customization options.

### Target Audience

- **UI/UX Designers:** Selecting typefaces for web and mobile applications
- **Web Developers:** Choosing fonts for implementation in projects
- **Graphic Designers:** Finding complementary fonts for branding
- **Typography Enthusiasts:** Exploring and comparing font characteristics

### Core Features (MVP)

1. **Font Catalog:** Browse available fonts from multiple providers
2. **Side-by-Side Comparison:** Compare up to 4 fonts simultaneously
3. **Custom Preview Text:** Enter custom text for realistic comparison
4. **Filter & Search:** Filter by category, popularity, weight, width
5. **Responsive Design:** Seamless experience across all devices
6. **Dark Mode:** Built-in theme toggle for comfortable viewing
7. **URL Sharing:** Share comparison sessions via shareable URLs

### Tech Stack

| Layer | Technology | Purpose |
|-------|-----------|---------|
| Framework | SvelteKit 2.x | Full-stack framework with SSR/SSG support |
| UI Language | Svelte 5 | Reactive component framework |
| Styling | Tailwind CSS 4.x | Utility-first CSS framework |
| Component Library | Bits UI | Accessible Svelte components (Radix UI port) |
| Type Safety | TypeScript 5.x | Static type checking |
| Package Manager | Yarn | Fast, reliable dependency management |
| Linting | oxlint | Fast Rust-based linter |
| Formatting | dprint | Fast Rust-based code formatter |
| Hosting | Vercel | Edge deployment & preview environments |

### Project Goals

#### Learning Goals (Primary)
- Gain proficiency in Svelte 5 and its reactive primitives (`$state`, `$derived`, `$effect`)
- Understand SvelteKit's routing and data loading architecture
- Learn client-side state management patterns in Svelte ecosystem
- Explore performance optimization techniques for static web apps

#### Project Goals (Secondary)
- Build a functional, visually appealing font comparison tool
- Create a performant, accessible user interface
- Establish a foundation for future commercialization
- Demonstrate mastery of modern frontend development practices

---

## Executive Summary

### Recommended Approach: Pure Client-Side Architecture

**Recommendation:** Build the MVP as a pure client-side application using SvelteKit's static site generation (SSG) capabilities, with no backend infrastructure.

### Key Rationale

1. **Learning Focus:** Minimize backend complexity to concentrate on Svelte/SvelteKit mastery
2. **Data Availability:** Font metadata is publicly available via Google Fonts API and Fontshare CDN
3. **Performance:** Static generation provides instant page loads and optimal Core Web Vitals
4. **Cost Efficiency:** No server costs during MVP phase
5. **Future Flexibility:** Can easily add backend later when user data collection becomes necessary

### Architecture at a Glance

```
┌─────────────────────────────────────────────────────────────┐
│                         User Browser                          │
│  ┌─────────────────────────────────────────────────────────┐  │
│  │              SvelteKit Client Application                │  │
│  │  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐      │  │
│  │  │  Font Store │  │ Filter Store│  │  Comp Store │      │  │
│  │  └─────────────┘  └─────────────┘  └─────────────┘      │  │
│  │  ┌─────────────────────────────────────────────────┐    │  │
│  │  │           Font Provider Services                 │    │  │
│  │  │  ┌──────────────┐  ┌──────────────┐             │    │  │
│  │  │  │ Google Fonts │  │  Fontshare   │             │    │  │
│  │  │  │    API       │  │    CDN       │             │    │  │
│  │  │  └──────────────┘  └──────────────┘             │    │  │
│  │  └─────────────────────────────────────────────────┘    │  │
│  └─────────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘
         │                                       │
         │ HTTP Requests                        │ CSS Font Files
         ▼                                       ▼
┌──────────────────┐                  ┌──────────────────┐
│ Google Fonts API │                  │ Fontshare CDN    │
└──────────────────┘                  └──────────────────┘
```

---

## Architecture Decisions

### Backend Necessity Analysis

#### Option A: Pure Client-Side (Recommended for MVP)

**Pros:**
- **Simplicity:** No server code, database, or API endpoints to maintain
- **Performance:** Static sites load faster and score better on Core Web Vitals
- **Cost:** Zero hosting costs on Vercel free tier
- **Learning Focus:** Maximum time spent on Svelte/SvelteKit fundamentals
- **Deployment:** Instant deployments with zero configuration
- **Scalability:** Vercel Edge handles CDN distribution automatically

**Cons:**
- **No User Data:** Cannot save user preferences or comparison history
- **No Analytics:** Limited to client-side analytics (e.g., Google Analytics)
- **Rate Limiting:** Google Fonts API has usage limits (1,000 requests/day)
- **Caching:** Cannot implement server-side caching strategies
- **Data Freshness:** Font metadata fetched on each session (mitigated by browser caching)

**Use Cases This Supports:**
- ✅ Browse and compare fonts
- ✅ Share comparisons via URL
- ✅ Filter and search fonts
- ✅ Save preferences locally (localStorage)
- ✅ Responsive, dark mode UI

**Use Cases This Does NOT Support:**
- ❌ User accounts and saved comparisons
- ❌ Custom font uploads
- ❌ Collaborative comparisons
- ❌ Advanced analytics

---

#### Option B: Hybrid with Serverless Backend

**Pros:**
- **Caching Layer:** Server-side caching reduces API calls and improves load times
- **Rate Limit Management:** Proxy requests to avoid Google Fonts API limits
- **User Data:** Save user preferences and comparison history
- **Custom Endpoints:** Create specialized API endpoints for font data
- **Preprocessing:** Transform and normalize font data before sending to client

**Cons:**
- **Complexity:** Additional infrastructure to build and maintain
- **Cost:** Vercel Pro plan may be required for serverless functions
- **Latency:** Server round-trip adds latency to initial page load
- **Development Overhead:** Testing backend code requires additional considerations
- **Learning Curve:** Takes time away from Svelte learning goals

**Recommended Backend Stack (if needed later):**
- **API Routes:** SvelteKit server endpoints (`+page.server.ts`, `+server.ts`)
- **Database:** Vercel Postgres (Neon) or SQLite (better-sqlite3)
- **Caching:** Vercel KV (Redis) or in-memory caching
- **Auth:** Lucia Auth or Clerk for user authentication

---

### Recommendation

**Build Option A (Pure Client-Side) for MVP with these considerations:**

1. **Design for future backend:** Structure data fetching and state management to be easily adapted to server-side later
2. **Implement smart caching:** Use browser localStorage for font metadata cache with TTL
3. **Optimize API usage:** Batch requests and use Google Fonts API efficiently
4. **Monitor usage:** Track API usage and user engagement to inform backend decision
5. **Migration path:** Keep server components clear of logic that could be moved to `+page.server.ts` later

### When to Add Backend

Consider adding backend when:
- ✅ User growth exceeds 1,000 daily active users
- ✅ Analytics show users repeatedly saving comparisons manually
- ✅ Feedback indicates desire for user accounts
- ✅ Performance degrades due to repeated API calls
- ✅ Planning to add premium features requiring payment processing

---

## Font Provider Integration Strategy

### Provider Overview

| Provider | API Type | License | Font Count | Integration Complexity |
|----------|----------|---------|------------|------------------------|
| Google Fonts | REST API | Open Source (SIL/OFL) | 1,600+ | Low - Official API available |
| Fontshare | GitHub/CDN | Free License | 100+ | Very Low - Static JSON available |

---

### Google Fonts Integration

#### API Endpoint

```
https://www.googleapis.com/webfonts/v1/webfonts?key=YOUR_API_KEY
```

#### TypeScript Implementation

```typescript
// src/lib/services/google-fonts.ts
import type { FontMetadata, FontVariant, FontCategory } from '$lib/types';

export interface GoogleFontsResponse {
  kind: string;
  items: GoogleFontItem[];
}

export interface GoogleFontItem {
  family: string;
  variants: string[];
  subsets: string[];
  version: string;
  lastModified: string;
  files: Record<string, string>;
  category: 'sans-serif' | 'serif' | 'display' | 'handwriting' | 'monospace';
}

export async function fetchGoogleFonts(apiKey: string): Promise<FontMetadata[]> {
  const response = await fetch(
    `https://www.googleapis.com/webfonts/v1/webfonts?key=${apiKey}`
  );

  if (!response.ok) {
    throw new Error(`Google Fonts API error: ${response.statusText}`);
  }

  const data: GoogleFontsResponse = await response.json();

  return data.items.map(mapGoogleFontToMetadata);
}

function mapGoogleFontToMetadata(item: GoogleFontItem): FontMetadata {
  const category = mapGoogleCategory(item.category);

  return {
    id: `google-${item.family.toLowerCase().replace(/\s+/g, '-')}`,
    provider: 'google-fonts',
    family: item.family,
    displayName: item.family,
    category,
    variants: mapGoogleVariants(item.variants),
    license: {
      type: 'open-source',
      url: 'https://fonts.google.com/attribution',
      attribution: 'Google Fonts',
      commercial: true,
      embedding: 'webfont'
    },
    languages: item.subsets,
    previewUrl: getGoogleFontPreviewUrl(item.family),
    cssUrl: getGoogleFontCssUrl(item.family, '400'),
    metadata: {
      version: item.version,
      lastModified: item.lastModified,
      files: item.files
    }
  };
}

function mapGoogleCategory(
  category: GoogleFontItem['category']
): FontCategory {
  const mapping = {
    'sans-serif': 'sans-serif',
    'serif': 'serif',
    'display': 'display',
    'handwriting': 'handwriting',
    'monospace': 'monospace'
  } as const;
  return mapping[category] || 'display';
}

function mapGoogleVariants(variants: string[]): FontVariant[] {
  return variants.map(v => {
    const weight = parseInt(v) || 400;
    const style = v.includes('italic') ? 'italic' : 'normal';
    return { weight, style, name: v };
  });
}

function getGoogleFontPreviewUrl(family: string): string {
  return `https://fonts.googleapis.com/css2?family=${encodeURIComponent(family)}:wght@400&display=swap`;
}

function getGoogleFontCssUrl(family: string, weight: string): string {
  return `https://fonts.googleapis.com/css2?family=${encodeURIComponent(family)}:wght@${weight}&display=swap`;
}
```

#### Dynamic Font Loading

```typescript
// src/lib/utils/font-loader.ts
let loadedFonts = new Set<string>();

export async function loadFont(family: string, weight: number = 400): Promise<void> {
  const fontKey = `${family}-${weight}`;

  if (loadedFonts.has(fontKey)) {
    return;
  }

  const cssUrl = `https://fonts.googleapis.com/css2?family=${encodeURIComponent(family)}:wght@${weight}&display=swap`;

  try {
    // Create and inject link element
    const link = document.createElement('link');
    link.rel = 'stylesheet';
    link.href = cssUrl;
    link.crossOrigin = 'anonymous';

    await new Promise<void>((resolve, reject) => {
      link.onload = () => {
        loadedFonts.add(fontKey);
        resolve();
      };
      link.onerror = () => reject(new Error(`Failed to load font: ${family}`));
      document.head.appendChild(link);
    });
  } catch (error) {
    console.error(`Failed to load font ${family}:`, error);
    throw error;
  }
}

export function unloadFont(family: string, weight: number = 400): void {
  const cssUrl = `https://fonts.googleapis.com/css2?family=${encodeURIComponent(family)}:wght@${weight}&display=swap`;
  const links = document.querySelectorAll(`link[href="${cssUrl}"]`);
  links.forEach(link => link.remove());
  loadedFonts.delete(`${family}-${weight}`);
}

export function preloadFonts(fonts: { family: string; weight: number }[]): void {
  fonts.forEach(({ family, weight }) => {
    const link = document.createElement('link');
    link.rel = 'preload';
    link.as = 'font';
    link.type = 'font/woff2';
    link.href = `https://fonts.gstatic.com/s/${family.toLowerCase()}/v${weight}`;
    link.crossOrigin = 'anonymous';
    document.head.appendChild(link);
  });
}
```

---

### Fontshare Integration

#### Data Source

Fontshare provides a static JSON file with all font metadata:

```
https://api.fontshare.com/v2/css?f[]=<font-family-name>
```

Alternative: Use the GitHub repository data or scrape from the website.

#### TypeScript Implementation

```typescript
// src/lib/services/fontshare.ts
import type { FontMetadata } from '$lib/types';

export interface FontshareMetadata {
  family: string;
  slug: string;
  styles: FontshareStyle[];
  subsets: string[];
  category: string;
}

export interface FontshareStyle {
  name: string;
  weight: number;
  file: string;
  unicodeRange?: string;
}

// Fontshare static font list (maintained manually or fetched from their docs)
const FONTHARE_FONTS: FontshareMetadata[] = [
  {
    family: 'Albert Sans',
    slug: 'albert-sans',
    styles: [
      { name: 'Regular', weight: 400, file: 'https://api.fontshare.com/v2/css?f[]=albert-sans@400' },
      { name: 'Medium', weight: 500, file: 'https://api.fontshare.com/v2/css?f[]=albert-sans@500' },
      { name: 'Bold', weight: 700, file: 'https://api.fontshare.com/v2/css?f[]=albert-sans@700' }
    ],
    subsets: ['latin', 'latin-ext'],
    category: 'sans-serif'
  },
  // Add more Fontshare fonts as needed...
];

export async function fetchFontshareFonts(): Promise<FontMetadata[]> {
  // In a real implementation, you might fetch this from a maintained JSON file
  // For MVP, we use the static list or fetch from Fontshare's API

  // Option 1: Use static list
  return FONTHARE_FONTS.map(mapFontshareToMetadata);

  // Option 2: Fetch from Fontshare API (if available)
  // const response = await fetch('https://api.fontshare.com/v2/fonts');
  // const data = await response.json();
  // return data.map(mapFontshareToMetadata);
}

function mapFontshareToMetadata(font: FontshareMetadata): FontMetadata {
  return {
    id: `fontshare-${font.slug}`,
    provider: 'fontshare',
    family: font.family,
    displayName: font.family,
    category: mapFontshareCategory(font.category),
    variants: font.styles.map(style => ({
      weight: style.weight,
      style: 'normal',
      name: style.name,
      url: style.file
    })),
    license: {
      type: 'open-source',
      url: 'https://www.fontshare.com/license',
      attribution: 'Fontshare',
      commercial: true,
      embedding: 'webfont'
    },
    languages: font.subsets,
    previewUrl: font.styles[0]?.file || '',
    cssUrl: font.styles[0]?.file || '',
    metadata: {
      slug: font.slug,
      styles: font.styles
    }
  };
}

function mapFontshareCategory(category: string): FontCategory {
  const validCategories: FontCategory[] = ['sans-serif', 'serif', 'display', 'handwriting', 'monospace'];
  const normalized = category.toLowerCase().replace(' ', '-');
  return validCategories.includes(normalized as FontCategory)
    ? (normalized as FontCategory)
    : 'display';
}
```

---

### Data Normalization

Both providers return different data structures. Normalize to a unified interface:

```typescript
// src/lib/types/fonts.ts
export type FontCategory = 'sans-serif' | 'serif' | 'display' | 'handwriting' | 'monospace';
export type FontProvider = 'google-fonts' | 'fontshare';

export interface LicenseInfo {
  type: 'open-source' | 'commercial' | 'free-for-personal';
  url: string;
  attribution: string;
  commercial: boolean;
  embedding: 'webfont' | 'self-host' | 'both';
}

export interface FontVariant {
  weight: number;
  style: 'normal' | 'italic';
  name: string;
  url?: string;
}

export interface FontMetadata {
  id: string;
  provider: FontProvider;
  family: string;
  displayName: string;
  category: FontCategory;
  variants: FontVariant[];
  license: LicenseInfo;
  languages: string[];
  previewUrl: string;
  cssUrl: string;
  popularity?: number; // For sorting
  trending?: boolean;
  metadata: Record<string, unknown>;
}

export interface ComparisonFont {
  font: FontMetadata;
  variant: FontVariant;
  size: number;
  lineHeight: number;
  letterSpacing: number;
  color: string;
  text?: string; // Override default preview text
}

export interface ComparisonSettings {
  text: string;
  backgroundColor: string;
  showGrid: boolean;
  watermark: boolean;
}
```

---

## Performance Optimization

### Lazy Loading Strategy

#### Font Lazy Loading

```typescript
// src/lib/hooks/useLazyFontLoader.ts
import { tick } from 'svelte';
import { loadFont } from '$lib/utils/font-loader';

export function useLazyFontLoader() {
  let observer: IntersectionObserver | null = null;
  let elementsToLoad = new Map<HTMLElement, { family: string; weight: number }>();

  function observe(
    element: HTMLElement,
    family: string,
    weight: number = 400
  ) {
    if (!observer) {
      observer = new IntersectionObserver(
        (entries) => {
          entries.forEach(async (entry) => {
            if (entry.isIntersecting) {
              const data = elementsToLoad.get(entry.target as HTMLElement);
              if (data) {
                await loadFont(data.family, data.weight);
                observer?.unobserve(entry.target);
                elementsToLoad.delete(entry.target as HTMLElement);
              }
            }
          });
        },
        {
          rootMargin: '200px', // Load before element enters viewport
          threshold: 0.01
        }
      );
    }

    elementsToLoad.set(element, { family, weight });
    observer.observe(element);
  }

  function destroy() {
    observer?.disconnect();
    observer = null;
    elementsToLoad.clear();
  }

  return { observe, destroy };
}
```

#### Component-Level Usage

```svelte
<!-- src/lib/components/FontPreview.svelte -->
<script lang="ts">
  import { onMount, onDestroy } from 'svelte';
  import { useLazyFontLoader } from '$lib/hooks/useLazyFontLoader';

  export let family: string;
  export let weight: number = 400;
  export let text: string = 'The quick brown fox jumps over the lazy dog';

  let element: HTMLElement;
  const { observe, destroy } = useLazyFontLoader();

  onMount(() => {
    observe(element, family, weight);
  });

  onDestroy(() => {
    destroy();
  });
</script>

<div
  bind:this={element}
  class="font-preview"
  style:font-family="{family}"
  style:font-weight="{weight}"
>
  {text}
</div>

<style>
  .font-preview {
    /* Ensure element has height for intersection observer */
    min-height: 48px;
  }
</style>
```

### Caching Strategy

#### localStorage Caching with TTL

```typescript
// src/lib/utils/cache.ts
const CACHE_KEY = 'glyphdiff:font-cache';
const CACHE_VERSION = 1;
const CACHE_TTL = 24 * 60 * 60 * 1000; // 24 hours

interface CacheEntry {
  version: number;
  timestamp: number;
  data: unknown;
}

export function setCache<T>(key: string, data: T, ttl: number = CACHE_TTL): void {
  const entry: CacheEntry = {
    version: CACHE_VERSION,
    timestamp: Date.now(),
    data
  };

  const cache = getCacheData();
  cache[key] = entry;

  try {
    localStorage.setItem(CACHE_KEY, JSON.stringify(cache));
  } catch (error) {
    console.warn('Failed to set cache:', error);
  }
}

export function getCache<T>(key: string): T | null {
  const cache = getCacheData();
  const entry = cache[key];

  if (!entry) {
    return null;
  }

  // Check version
  if (entry.version !== CACHE_VERSION) {
    delete cache[key];
    saveCacheData(cache);
    return null;
  }

  // Check TTL
  if (Date.now() - entry.timestamp > CACHE_TTL) {
    delete cache[key];
    saveCacheData(cache);
    return null;
  }

  return entry.data as T;
}

export function clearCache(key?: string): void {
  if (key) {
    const cache = getCacheData();
    delete cache[key];
    saveCacheData(cache);
  } else {
    localStorage.removeItem(CACHE_KEY);
  }
}

function getCacheData(): Record<string, CacheEntry> {
  try {
    const cached = localStorage.getItem(CACHE_KEY);
    return cached ? JSON.parse(cached) : {};
  } catch {
    return {};
  }
}

function saveCacheData(data: Record<string, CacheEntry>): void {
  try {
    localStorage.setItem(CACHE_KEY, JSON.stringify(data));
  } catch (error) {
    console.warn('Failed to save cache:', error);
  }
}
```

#### Service Worker Caching (Optional for Enhanced PWA)

```typescript
// src/lib/service-worker.ts
const CACHE_NAME = 'glyphdiff-v1';
const FONT_CACHE_PREFIX = 'font-';

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME).then((cache) => {
      return cache.addAll([
        '/',
        '/fonts',
        '/compare',
        // Add other static assets
      ]);
    })
  );
});

self.addEventListener('fetch', (event) => {
  const url = new URL(event.request.url);

  // Cache Google Fonts
  if (url.hostname === 'fonts.googleapis.com' || url.hostname === 'fonts.gstatic.com') {
    event.respondWith(
      caches.open(`${FONT_CACHE_PREFIX}${CACHE_NAME}`).then((cache) => {
        return cache.match(event.request).then((response) => {
          if (response) {
            return response;
          }
          return fetch(event.request).then((networkResponse) => {
            cache.put(event.request, networkResponse.clone());
            return networkResponse;
          });
        });
      })
    );
    return;
  }

  // Network-first for API calls
  if (url.pathname.includes('/api/')) {
    event.respondWith(
      fetch(event.request)
        .then((response) => {
          const responseClone = response.clone();
          caches.open(CACHE_NAME).then((cache) => {
            cache.put(event.request, responseClone);
          });
          return response;
        })
        .catch(() => caches.match(event.request))
    );
    return;
  }

  // Cache-first for static assets
  event.respondWith(
    caches.match(event.request).then((response) => {
      return response || fetch(event.request);
    })
  );
});
```

### Performance Metrics

#### Target Core Web Vitals

| Metric | Target | Why It Matters |
|--------|--------|----------------|
| LCP (Largest Contentful Paint) | < 2.5s | Main content loads quickly |
| FID (First Input Delay) | < 100ms | Responsive to user input |
| CLS (Cumulative Layout Shift) | < 0.1 | Visual stability |
| TTFB (Time to First Byte) | < 600ms | Fast initial response |

#### Performance Monitoring

```typescript
// src/lib/utils/performance.ts
export function reportWebVitals(): void {
  if (typeof window === 'undefined' || !('PerformanceObserver' in window)) {
    return;
  }

  // LCP
  const lcpObserver = new PerformanceObserver((list) => {
    const entries = list.getEntries();
    const lastEntry = entries[entries.length - 1] as any;
    console.log('LCP:', lastEntry.startTime);
    // Send to analytics
  });
  lcpObserver.observe({ entryTypes: ['largest-contentful-paint'] });

  // FID
  const fidObserver = new PerformanceObserver((list) => {
    const entries = list.getEntries();
    const fid = entries[0] as any;
    console.log('FID:', fid.processingStart - fid.startTime);
    // Send to analytics
  });
  fidObserver.observe({ entryTypes: ['first-input'] });

  // CLS
  const clsObserver = new PerformanceObserver((list) => {
    let clsValue = 0;
    for (const entry of list.getEntries() as any[]) {
      if (!entry.hadRecentInput) {
        clsValue += entry.value;
      }
    }
    console.log('CLS:', clsValue);
    // Send to analytics
  });
  clsObserver.observe({ entryTypes: ['layout-shift'] });
}
```

---

## Frontend Architecture

### Project Structure

```
glyphdiff/
├── src/
│   ├── lib/
│   │   ├── components/
│   │   │   ├── FontCard.svelte
│   │   │   ├── FontPreview.svelte
│   │   │   ├── ComparisonGrid.svelte
│   │   │   ├── FilterBar.svelte
│   │   │   └── DarkModeToggle.svelte
│   │   ├── stores/
│   │   │   ├── fontStore.ts
│   │   │   ├── comparisonStore.ts
│   │   │   ├── filterStore.ts
│   │   │   └── uiStore.ts
│   │   ├── services/
│   │   │   ├── google-fonts.ts
│   │   │   ├── fontshare.ts
│   │   │   └── font-loader.ts
│   │   ├── hooks/
│   │   │   ├── useLazyFontLoader.ts
│   │   │   ├── useKeyboardShortcuts.ts
│   │   │   └── useLocalStorage.ts
│   │   ├── utils/
│   │   │   ├── cache.ts
│   │   │   ├── format.ts
│   │   │   └── url.ts
│   │   ├── types/
│   │   │   ├── fonts.ts
│   │   │   ├── comparison.ts
│   │   │   └── index.ts
│   │   └── constants.ts
│   ├── routes/
│   │   ├── +layout.svelte
│   │   ├── +layout.ts
│   │   ├── +page.svelte           # Home page
│   │   ├── fonts/
│   │   │   ├── +page.svelte       # Font catalog
│   │   │   ├── +page.ts           # Font data loading
│   │   │   └── [slug]/
│   │   │       └── +page.svelte   # Font detail page
│   │   └── compare/
│   │       ├── +page.svelte       # Comparison page
│   │       └── +page.ts           # URL state parsing
│   ├── app.css
│   └── app.d.ts
├── static/
│   ├── favicon.ico
│   └── og-image.png
├── tests/
│   ├── unit/
│   └── e2e/
├── package.json
├── svelte.config.js
├── tailwind.config.js
├── tsconfig.json
└── vite.config.ts
```

### Component Architecture

```
┌────────────────────────────────────────────────────────────┐
│                        +layout.svelte                        │
│  ┌──────────────────────────────────────────────────────┐  │
│  │                   Header                               │  │
│  │  Logo | Search | DarkModeToggle                       │  │
│  └──────────────────────────────────────────────────────┘  │
│  ┌──────────────────────────────────────────────────────┐  │
│  │                      Main                              │  │
│  │  ┌────────────────────────────────────────────────┐  │  │
│  │  │              +page.svelte (Home)                 │  │  │
│  │  │  Hero section → Featured fonts → CTA            │  │  │
│  │  └────────────────────────────────────────────────┘  │  │
│  │  ┌────────────────────────────────────────────────┐  │  │
│  │  │             fonts/+page.svelte                   │  │  │
│  │  │  FilterBar → FontGrid → FontCard                │  │  │
│  │  │  ┌─────────┐  ┌─────────┐  ┌─────────┐          │  │  │
│  │  │  │FontCard │  │FontCard │  │FontCard │  ...     │  │  │
│  │  │  └─────────┘  └─────────┘  └─────────┘          │  │  │
│  │  └────────────────────────────────────────────────┘  │  │
│  │  ┌────────────────────────────────────────────────┐  │  │
│  │  │           compare/+page.svelte                   │  │  │
│  │  │  ComparisonGrid → FontPreview × 4                │  │  │
│  │  │  Toolbar (text, size, color, settings)          │  │  │
│  │  └────────────────────────────────────────────────┘  │  │
│  └──────────────────────────────────────────────────────┘  │
│  ┌──────────────────────────────────────────────────────┐  │
│  │                   Footer                               │  │
│  └──────────────────────────────────────────────────────┘  │
└────────────────────────────────────────────────────────────┘
```

### Routing Strategy

#### SvelteKit File-Based Routing

| Route | File | Purpose | SSR/CSR |
|-------|------|---------|---------|
| `/` | `routes/+page.svelte` | Home/Landing page | SSR |
| `/fonts` | `routes/fonts/+page.svelte` | Font catalog | SSG |
| `/fonts/[slug]` | `routes/fonts/[slug]/+page.svelte` | Font details | SSG |
| `/compare` | `routes/compare/+page.svelte` | Comparison tool | CSR |
| `/api/...` | `routes/api/+server.ts` | Future API routes | Serverless |

#### URL State for Comparisons

```typescript
// src/routes/compare/+page.ts
import type { PageLoad } from './$types';

export const load: PageLoad = ({ url }) => {
  const searchParams = url.searchParams;

  // Parse comparison state from URL
  const fontsParam = searchParams.get('fonts');
  const text = searchParams.get('text') || 'The quick brown fox...';
  const size = parseInt(searchParams.get('size') || '24');
  const darkMode = searchParams.get('dark') === 'true';

  let comparisonFonts: Array<{ family: string; weight: number }> = [];

  if (fontsParam) {
    try {
      comparisonFonts = JSON.parse(decodeURIComponent(fontsParam));
    } catch (e) {
      console.error('Failed to parse fonts param:', e);
    }
  }

  return {
    initialFonts: comparisonFonts,
    settings: { text, size, darkMode }
  };
};
```

```svelte
<!-- src/routes/compare/+page.svelte -->
<script lang="ts">
  import { page } from '$app/stores';
  import { goto } from '$app/navigation';
  import { comparisonStore } from '$lib/stores/comparisonStore';
  import type { PageData } from './$types';

  export let data: PageData;

  // Initialize store from URL
  $: comparisonStore.setSettings(data.settings);
  $: comparisonStore.setFonts(data.initialFonts);

  // Sync URL changes
  $: {
    if (comparisonStore.shareable) {
      const url = new URL(window.location.href);
      url.searchParams.set(
        'fonts',
        JSON.stringify(comparisonStore.fonts.map(f => ({ family: f.font.family, weight: f.variant.weight })))
      );
      url.searchParams.set('text', comparisonStore.settings.text);
      url.searchParams.set('size', comparisonStore.settings.size.toString());

      // Only update URL without full navigation
      window.history.replaceState({}, '', url.toString());
    }
  }
</script>
```

---

## Data Models

### Core Type Definitions

```typescript
// src/lib/types/fonts.ts

/**
 * Font provider sources
 */
export type FontProvider = 'google-fonts' | 'fontshare';

/**
 * Standard font categories
 */
export type FontCategory =
  | 'sans-serif'
  | 'serif'
  | 'display'
  | 'handwriting'
  | 'monospace';

/**
 * License information for fonts
 */
export interface LicenseInfo {
  /** License type classification */
  type: 'open-source' | 'commercial' | 'free-for-personal';

  /** URL to full license text */
  url: string;

  /** Attribution required for display */
  attribution: string;

  /** Commercial use permitted */
  commercial: boolean;

  /** Allowed embedding methods */
  embedding: 'webfont' | 'self-host' | 'both';
}

/**
 * Individual font variant (weight/style combination)
 */
export interface FontVariant {
  /** Font weight (100-900) */
  weight: number;

  /** Font style */
  style: 'normal' | 'italic';

  /** Display name for the variant */
  name: string;

  /** URL to the font file (CSS or WOFF2) */
  url?: string;

  /** Subset information (optional) */
  subset?: string;
}

/**
 * Complete metadata for a font family
 */
export interface FontMetadata {
  /** Unique identifier for the font */
  id: string;

  /** Source provider */
  provider: FontProvider;

  /** Font family name (CSS property value) */
  family: string;

  /** Display name for UI */
  displayName: string;

  /** Font category */
  category: FontCategory;

  /** Available variants */
  variants: FontVariant[];

  /** License information */
  license: LicenseInfo;

  /** Supported language subsets */
  languages: string[];

  /** URL for font preview (CSS) */
  previewUrl: string;

  /** URL for CSS import */
  cssUrl: string;

  /** Popularity score (for sorting) */
  popularity?: number;

  /** Trending status */
  trending?: boolean;

  /** Additional provider-specific metadata */
  metadata: Record<string, unknown>;
}

/**
 * Font with selected variant for display
 */
export interface ActiveFont {
  /** Font metadata */
  font: FontMetadata;

  /** Selected variant */
  variant: FontVariant;
}

/**
 * Filter options for font catalog
 */
export interface FontFilters {
  /** Category filter */
  categories: FontCategory[];

  /** Weight range filter */
  weightRange: [number, number];

  /** Provider filter */
  providers: FontProvider[];

  /** Language subset filter */
  languages: string[];

  /** Search query */
  search: string;

  /** Sort option */
  sortBy: 'popularity' | 'name' | 'recent' | 'trending';

  /** Sort direction */
  sortDirection: 'asc' | 'desc';
}
```

```typescript
// src/lib/types/comparison.ts

import type { FontMetadata, FontVariant } from './fonts';

/**
 * Display settings for comparison preview
 */
export interface FontDisplaySettings {
  /** Font size in pixels */
  size: number;

  /** Line height (unitless multiplier) */
  lineHeight: number;

  /** Letter spacing in pixels */
  letterSpacing: number;

  /** Text color */
  color: string;

  /** Custom preview text override */
  text?: string;

  /** Text alignment */
  textAlign: 'left' | 'center' | 'right';
}

/**
 * Global comparison settings
 */
export interface ComparisonSettings {
  /** Default preview text */
  text: string;

  /** Background color */
  backgroundColor: string;

  /** Show comparison grid lines */
  showGrid: boolean;

  /** Show watermarks/attribution */
  watermark: boolean;

  /** Default display settings */
  display: FontDisplaySettings;
}

/**
 * Font in a comparison session
 */
export interface ComparisonFont {
  /** Font metadata */
  font: FontMetadata;

  /** Selected variant */
  variant: FontVariant;

  /** Display settings (overrides global) */
  settings: Partial<FontDisplaySettings>;
}

/**
 * Complete comparison session
 */
export interface ComparisonSession {
  /** Unique session identifier */
  id: string;

  /** Fonts being compared (max 4) */
  fonts: ComparisonFont[];

  /** Global comparison settings */
  settings: ComparisonSettings;

  /** Session metadata */
  metadata: {
    /** Creation timestamp */
    createdAt: number;

    /** Last modified timestamp */
    updatedAt: number;

    /** Session name */
    name?: string;

    /** Whether session is saved */
    saved: boolean;
  };
}

/**
 * Shareable comparison data (for URL encoding)
 */
export interface ShareableComparison {
  /** Font identifiers and weights */
  fonts: Array<{ family: string; weight: number }>;

  /** Preview text */
  text?: string;

  /** Font size */
  size?: number;

  /** Dark mode flag */
  dark?: boolean;
}
```

```typescript
// src/lib/types/ui.ts

/**
 * UI theme options
 */
export type Theme = 'light' | 'dark' | 'system';

/**
 * UI settings persisted in localStorage
 */
export interface UISettings {
  /** Selected theme */
  theme: Theme;

  /** Grid view density */
  gridDensity: 'compact' | 'comfortable' | 'spacious';

  /** Show font variants in catalog */
  showVariants: boolean;

  /** Enable animations */
  animationsEnabled: boolean;
}

/**
 * Toast notification types
 */
export type ToastType = 'success' | 'error' | 'info' | 'warning';

/**
 * Toast notification
 */
export interface Toast {
  id: string;
  type: ToastType;
  message: string;
  duration?: number;
  action?: {
    label: string;
    handler: () => void;
  };
}

/**
 * Keyboard shortcut definition
 */
export interface KeyboardShortcut {
  key: string;
  ctrl?: boolean;
  shift?: boolean;
  alt?: boolean;
  description: string;
  action: () => void;
}

/**
 * Modal/Dialog state
 */
export interface ModalState {
  id: string | null;
  open: boolean;
  props?: Record<string, unknown>;
}
```

```typescript
// src/lib/types/index.ts

// Re-export all types for convenient importing
export * from './fonts';
export * from './comparison';
export * from './ui';
```

---

## Implementation Roadmap

### Week 1: Svelte Fundamentals

**Goal:** Build foundational understanding of Svelte 5 reactive primitives and set up development environment.

#### Tasks

- [ ] **Project Setup**
  - [ ] Create SvelteKit project with TypeScript template
  - [ ] Install and configure Tailwind CSS 4.x
  - [ ] Install and set up Bits UI component library
  - [ ] Configure oxlint and dprint for linting and formatting
  - [ ] Set up Git repository and .gitignore

- [ ] **Environment Configuration**
  - [ ] Create `.env.example` with GOOGLE_FONTS_API_KEY
  - [ ] Add `.env` to `.gitignore`
  - [ ] Configure environment variable loading in `vite.config.ts`

- [ ] **Core Types Definition**
  - [ ] Create `src/lib/types/fonts.ts`
  - [ ] Create `src/lib/types/comparison.ts`
  - [ ] Create `src/lib/types/ui.ts`
  - [ ] Create `src/lib/types/index.ts` for re-exports

- [ ] **Svelte 5 Reactive Primitives Practice**
  - [ ] Build Counter component using `$state`
  - [ ] Create DerivedCounter component using `$derived`
  - [ ] Implement EffectLogger component using `$effect`
  - [ ] Practice with reactive arrays and objects

- [ ] **Practice Components**
  - [ ] Build simple Button component
  - [ ] Create Toggle component
  - [ ] Implement Select dropdown component
  - [ ] Build simple FilterBar component

#### Learning Outcomes
- Understand Svelte 5's new runes system (`$state`, `$derived`, `$effect`)
- Comfortable with Svelte component structure and syntax
- Familiar with Bits UI components
- Tailwind CSS integration working

#### Week 1 Deliverables
- Working development environment
- 4 practice components demonstrating Svelte reactivity
- Core TypeScript types defined

---

### Week 2: SvelteKit & Routing

**Goal:** Build font catalog page with routing, data fetching, and understand SvelteKit's SSR capabilities.

#### Tasks

- [ ] **Google Fonts Service**
  - [ ] Create `fetchGoogleFonts()` function
  - [ ] Implement `mapGoogleFontToMetadata()` mapper
  - [ ] Add TypeScript interfaces for Google Fonts API response
  - [ ] Test with Google Fonts API key

- [ ] **Fontshare Service**
  - [ ] Create `fetchFontshareFonts()` function
  - [ ] Build static font list for Fontshare
  - [ ] Implement `mapFontshareToMetadata()` mapper
  - [ ] Combine both providers into single font catalog

- [ ] **Font Catalog Page**
  - [ ] Create `routes/fonts/+page.svelte`
  - [ ] Implement `routes/fonts/+page.ts` for data loading
  - [ ] Build FontCard component
  - [ ] Create responsive FontGrid layout

- [ ] **Font Detail Page**
  - [ ] Create `routes/fonts/[slug]/+page.svelte`
  - [ ] Implement dynamic route parameter extraction
  - [ ] Build font detail view with all variants
  - [ ] Add "Add to Comparison" button

- [ ] **Comparison Page Skeleton**
  - [ ] Create `routes/compare/+page.svelte`
  - [ ] Implement URL state parsing in `+page.ts`
  - [ ] Build basic layout for comparison grid

- [ ] **SSR Understanding**
  - [ ] Explore SvelteKit rendering modes (SSR, CSR, SSG)
  - [ ] Test page performance with SSR enabled
  - [ ] Understand hydration process
  - [ ] Configure static generation for font catalog

#### Learning Outcomes
- Understand SvelteKit file-based routing
- Learn data loading patterns (`+page.ts`, `+page.server.ts`)
- Grasp SSR vs CSR concepts and trade-offs
- Comfortable with dynamic routes and parameters

#### Week 2 Deliverables
- Working font catalog page with Google Fonts data
- Font detail pages with all metadata
- Basic comparison page with URL state
- Understanding of SvelteKit rendering modes

---

### Week 3: State Management

**Goal:** Implement comprehensive state management with Svelte stores, localStorage persistence, and URL state synchronization.

#### Tasks

- [ ] **Font Store**
  - [ ] Create `src/lib/stores/fontStore.ts`
  - [ ] Implement `$state` for fonts array
  - [ ] Add derived state for filtered fonts
  - [ ] Implement localStorage persistence
  - [ ] Add loading and error states

- [ ] **Filter Store**
  - [ ] Create `src/lib/stores/filterStore.ts`
  - [ ] Implement `$state` for all filter options
  - [ ] Add derived state for active filter count
  - [ ] Implement reset filters function
  - [ ] Add localStorage persistence

- [ ] **Comparison Store**
  - [ ] Create `src/lib/stores/comparisonStore.ts`
  - [ ] Implement `$state` for comparison fonts (max 4)
  - [ ] Add functions to add/remove fonts
  - [ ] Implement comparison settings state
  - [ ] Add shareable URL generation
  - [ ] Implement localStorage persistence

- [ ] **UI Store**
  - [ ] Create `src/lib/stores/uiStore.ts`
  - [ ] Implement theme toggle logic
  - [ ] Add settings for grid density, animations
  - [ ] Implement system theme detection
  - [ ] Add localStorage persistence

- [ ] **Cache Utility**
  - [ ] Implement `cache.ts` with TTL support
  - [ ] Add caching to Google Fonts fetcher
  - [ ] Implement cache invalidation logic
  - [ ] Add cache management UI (optional)

- [ ] **URL State Integration**
  - [ ] Sync comparison state with URL
  - [ ] Sync filter state with URL (optional)
  - [ ] Implement deep linking to comparisons
  - [ ] Handle URL encoding/decoding

#### Learning Outcomes
- Master Svelte 5 stores with `$state` runes
- Understand localStorage persistence patterns
- Learn URL state synchronization
- Practice derived state and computed values

#### Week 3 Deliverables
- Fully functional stores for fonts, filters, comparisons, UI
- localStorage persistence working
- URL state synchronization working
- Caching layer implemented

---

### Week 4: UI & Polish

**Goal:** Build polished UI with Bits UI components, dark mode, responsive design, and smooth animations.

#### Tasks

- [ ] **Layout Components**
  - [ ] Build Header component with logo and navigation
  - [ ] Create Footer component with links and attribution
  - [ ] Implement global layout in `+layout.svelte`
  - [ ] Add mobile navigation menu

- [ ] **FilterBar Component**
  - [ ] Use Bits UI Select for category filter
  - [ ] Use Bits UI Dialog for advanced filters
  - [ ] Add search input with debouncing
  - [ ] Implement active filter indicators

- [ ] **ComparisonGrid Component**
  - [ ] Use Bits UI Grid for responsive layout
  - [ ] Implement drag-and-drop reordering (optional)
  - [ ] Add font settings panel per column
  - [ ] Implement "Remove font" button

- [ ] **FontPreview Component**
  - [ ] Build preview text area
  - [ ] Add size, weight, line-height controls
  - [ ] Implement color picker
  - [ ] Add lazy loading for fonts

- [ ] **Dark Mode**
  - [ ] Implement dark mode toggle
  - [ ] Configure Tailwind dark mode classes
  - [ ] Add system preference detection
  - [ ] Test color contrast in both themes

- [ ] **Responsive Design**
  - [ ] Test on mobile (375px)
  - [ ] Test on tablet (768px)
  - [ ] Test on desktop (1280px+)
  - [ ] Adjust grid columns for breakpoints

- [ ] **Animations & Transitions**
  - [ ] Add page transitions using Svelte transitions
  - [ ] Implement loading skeletons
  - [ ] Add hover effects on FontCard
  - [ ] Create toast notification system

- [ ] **Accessibility**
  - [ ] Add ARIA labels to interactive elements
  - [ ] Ensure keyboard navigation works
  - [ ] Test with screen reader
  - [ ] Verify color contrast ratios

- [ ] **Performance Optimization**
  - [ ] Implement image/font lazy loading
  - [ ] Add code splitting where appropriate
  - [ ] Test Lighthouse scores
  - [ ] Optimize bundle size

#### Learning Outcomes
- Proficient with Bits UI component library
- Comfortable building responsive layouts
- Understand accessibility best practices
- Experience with performance optimization

#### Week 4 Deliverables
- Polished, production-ready UI
- Dark mode fully implemented
- Responsive design across all breakpoints
- Accessibility improvements completed
- Performance targets met

---

## TanStack Query Research

### What is TanStack Query?

TanStack Query (formerly React Query) is a powerful data synchronization library for fetching, caching, and managing asynchronous state. It's widely used in the React ecosystem.

### Key Features

- **Automatic caching and refetching**
- **Loading and error state management**
- **Optimistic updates**
- **Pagination support**
- **Request deduplication**

### TanStack Query for Svelte?

TanStack Query has a Svelte implementation (`@tanstack/svelte-query`) that provides similar functionality to the React version.

### Why TanStack Query is NOT Recommended for MVP

| Factor | TanStack Query | SvelteKit Load | Recommendation |
|--------|----------------|----------------|----------------|
| **Data Source** | Client-side API calls | Server-side data loading | SvelteKit Load is sufficient |
| **Complexity** | Additional dependency | Built-in to framework | SvelteKit reduces complexity |
| **SSR Support** | Requires hydration | Native SSR | SvelteKit is cleaner |
| **Learning Curve** | Additional concepts to learn | Learn SvelteKit once | Focus on SvelteKit |
| **Bundle Size** | ~13KB gzipped | 0KB (built-in) | Smaller bundle |
| **Type Safety** | Good | Excellent | SvelteKit with TS is robust |
| **Caching Strategy** | In-memory cache | Static generation + CDN | SSG is more performant |

### Use Cases Where TanStack Query Would Be Useful

Consider adding TanStack Query in the future if:
- Implementing user authentication and profile data
- Building real-time features (WebSocket, polling)
- Complex pagination with infinite scroll
- Multiple API endpoints requiring complex cache invalidation
- Offline-first functionality

### Recommended Data Fetching Approach for MVP

#### Use SvelteKit's Data Loading

```typescript
// ✅ Recommended: SvelteKit load function
// src/routes/fonts/+page.ts
import { fetchGoogleFonts, fetchFontshareFonts } from '$lib/services';
import { setCache, getCache } from '$lib/utils/cache';

export const load = async ({ fetch, depends }) => {
  // Check cache first
  const cached = getCache('font-catalog');
  if (cached) {
    return { fonts: cached, cached: true };
  }

  // Fetch from providers
  const [googleFonts, fontshareFonts] = await Promise.all([
    fetchGoogleFonts(import.meta.env.VITE_GOOGLE_FONTS_API_KEY),
    fetchFontshareFonts()
  ]);

  const allFonts = [...googleFonts, ...fontshareFonts];

  // Cache for 24 hours
  setCache('font-catalog', allFonts);

  // Invalidate cache when needed
  depends('app:fonts');

  return { fonts: allFonts, cached: false };
};
```

#### Use Svelte Stores for Client-Side State

```typescript
// ✅ Recommended: Svelte 5 stores with $state
// src/lib/stores/fontStore.ts
import { setCache, getCache } from '$lib/utils/cache';

class FontStore {
  fonts = $state<FontMetadata[]>([]);
  loading = $state(false);
  error = $state<Error | null>(null);

  async loadFonts(apiKey: string) {
    this.loading = true;
    this.error = null;

    try {
      const cached = getCache('font-catalog');
      if (cached) {
        this.fonts = cached;
        return;
      }

      const [googleFonts, fontshareFonts] = await Promise.all([
        fetchGoogleFonts(apiKey),
        fetchFontshareFonts()
      ]);

      this.fonts = [...googleFonts, ...fontshareFonts];
      setCache('font-catalog', this.fonts);
    } catch (e) {
      this.error = e as Error;
    } finally {
      this.loading = false;
    }
  }
}

export const fontStore = new FontStore();
```

### Conclusion: Do NOT Use TanStack Query for MVP

**Reasoning:**
1. SvelteKit's data loading capabilities are sufficient for this project's needs
2. Focus on learning Svelte 5 and SvelteKit rather than adding more dependencies
3. Static generation provides better performance than client-side caching
4. Simpler codebase is easier to maintain while learning

**Future Consideration:**
Revisit this decision if the project grows to include:
- User authentication
- Real-time features
- Complex client-side data synchronization

---

## Learning Guide: React → Svelte

### React vs Svelte 5 Comparison

| React Concept | Svelte 5 Equivalent | Notes |
|--------------|---------------------|-------|
| `useState` | `$state` | No setter function needed, direct reassignment triggers reactivity |
| `useEffect` | `$effect` | Auto-tracks dependencies, no dependency array needed |
| `useMemo` | `$derived` | Computed values that automatically update |
| `useCallback` | Direct function | Functions are auto-memoized in Svelte 5 |
| `children` prop | `<slot />` | Slot composition with named slots |
| `props` | `export let` | Props declared with `export let propName` |
| `context` | `setContext` / `getContext` | Similar but with cleaner API |
| `useRef` | `bind:this` | Direct element binding instead of ref objects |
| `useState(prev => prev + 1)` | `count += 1` | Direct mutation works with $state |
| `useReducer` | Custom store with methods | Svelte stores are more flexible |
| `forwardRef` | N/A | Ref forwarding handled automatically |
| `useImperativeHandle` | N/A | Call methods directly on component instances |

### Code Examples

#### Counter Component

**React:**

```tsx
import { useState, useEffect } from 'react';

function Counter({ initial = 0 }: { initial?: number }) {
  const [count, setCount] = useState(initial);
  const [doubled, setDoubled] = useState(0);

  useEffect(() => {
    setDoubled(count * 2);
  }, [count]);

  return (
    <div>
      <h2>Count: {count}</h2>
      <h3>Doubled: {doubled}</h3>
      <button onClick={() => setCount(c => c + 1)}>Increment</button>
      <button onClick={() => setCount(c => c - 1)}>Decrement</button>
    </div>
  );
}
```

**Svelte 5:**

```svelte
<script lang="ts">
  export let initial = 0;

  let count = $state(initial);

  // $derived auto-updates when count changes
  let doubled = $derived(count * 2);

  function increment() {
    count += 1;
  }

  function decrement() {
    count -= 1;
  }
</script>

<div>
  <h2>Count: {count}</h2>
  <h3>Doubled: {doubled}</h3>
  <button onclick={increment}>Increment</button>
  <button onclick={decrement}>Decrement</button>
</div>
```

**Key Differences:**
- No setter function needed - direct mutation works with `$state`
- `$derived` eliminates need for `useEffect` with dependencies
- Functions are defined separately (no need for `useCallback`)
- Event handlers use lowercase `onclick` instead of `onClick`

---

#### Data Fetching

**React with React Query:**

```tsx
import { useQuery } from '@tanstack/react-query';

function FontList() {
  const {
    data: fonts,
    isLoading,
    error
  } = useQuery({
    queryKey: ['fonts'],
    queryFn: async () => {
      const response = await fetch('/api/fonts');
      if (!response.ok) throw new Error('Failed to fetch');
      return response.json();
    }
  });

  if (isLoading) return <div>Loading...</div>;
  if (error) return <div>Error: {error.message}</div>;

  return (
    <ul>
      {fonts.map((font: any) => (
        <li key={font.id}>{font.displayName}</li>
      ))}
    </ul>
  );
}
```

**SvelteKit with load function:**

```typescript
// +page.ts
export const load = async ({ fetch }) => {
  const response = await fetch('https://www.googleapis.com/webfonts/v1/webfonts?key=' + import.meta.env.VITE_GOOGLE_FONTS_API_KEY);
  const fonts = await response.json();
  return { fonts };
};
```

```svelte
<!-- +page.svelte -->
<script lang="ts">
  export let data;

  // data.fonts is available here, loaded on the server
</script>

{#if data.fonts}
  <ul>
    {#each data.fonts as font}
      <li>{font.family}</li>
    {/each}
  </ul>
{/if}
```

**Key Differences:**
- SvelteKit loads data on the server (SSR) by default
- No loading state needed for initial page load
- Data flows from `load` function to page component via props

---

#### State Management

**React with Zustand:**

```ts
// store.ts
import { create } from 'zustand';

interface FontStore {
  fonts: FontMetadata[];
  selectedFont: string | null;
  setFonts: (fonts: FontMetadata[]) => void;
  selectFont: (id: string) => void;
}

export const useFontStore = create<FontStore>((set) => ({
  fonts: [],
  selectedFont: null,
  setFonts: (fonts) => set({ fonts }),
  selectFont: (id) => set({ selectedFont: id })
}));
```

```tsx
// Component.tsx
import { useFontStore } from './store';

function FontSelector() {
  const { fonts, selectedFont, selectFont } = useFontStore();

  return (
    <select
      value={selectedFont || ''}
      onChange={(e) => selectFont(e.target.value)}
    >
      <option value="">Select a font</option>
      {fonts.map((font) => (
        <option key={font.id} value={font.id}>
          {font.displayName}
        </option>
      ))}
    </select>
  );
}
```

**Svelte with Store:**

```ts
// fontStore.ts
import type { FontMetadata } from '$lib/types';

class FontStore {
  fonts = $state<FontMetadata[]>([]);
  selectedFont = $state<string | null>(null);

  setFonts(fonts: FontMetadata[]) {
    this.fonts = fonts;
  }

  selectFont(id: string) {
    this.selectedFont = id;
  }
}

export const fontStore = new FontStore();
```

```svelte
<!-- FontSelector.svelte -->
<script lang="ts">
  import { fontStore } from '$lib/stores/fontStore';
</script>

<select bind:value={fontStore.selectedFont}>
  <option value="">Select a font</option>
  {#each fontStore.fonts as font}
    <option value={font.id}>
      {font.displayName}
    </option>
  {/each}
</select>
```

**Key Differences:**
- Svelte stores use `$state` directly, no need for immer
- Two-way binding with `bind:value` instead of `onChange`
- Store access is simpler - just import and use

---

#### Conditional Rendering

**React:**

```tsx
function ConditionalRender({ fonts, loading }: { fonts: Font[]; loading: boolean }) {
  if (loading) {
    return <Spinner />;
  }

  if (fonts.length === 0) {
    return <EmptyState message="No fonts found" />;
  }

  return (
    <div>
      {fonts.map(font => (
        <FontCard key={font.id} font={font} />
      ))}
    </div>
  );
}
```

**Svelte:**

```svelte
<script lang="ts">
  export let fonts: Font[];
  export let loading: boolean;
</script>

{#if loading}
  <Spinner />
{:else if fonts.length === 0}
  <EmptyState message="No fonts found" />
{:else}
  <div>
    {#each fonts as font}
      <FontCard {font} />
    {/each}
  </div>
{/if}
```

**Key Differences:**
- Svelte uses `{#if}`, `{:else if}`, `{:else}`, `{/if}` block syntax
- No ternary operator needed inside JSX
- `{#each}` block with `{/each}` for lists

---

#### Component Props

**React:**

```tsx
interface FontCardProps {
  font: FontMetadata;
  onClick?: (font: FontMetadata) => void;
  size?: number;
  showLicense?: boolean;
}

function FontCard({ font, onClick, size = 16, showLicense = false }: FontCardProps) {
  return (
    <div className="font-card" style={{ fontSize: size }}>
      <h3>{font.displayName}</h3>
      {showLicense && <LicenseInfo license={font.license} />}
      {onClick && <button onClick={() => onClick(font)}>Select</button>}
    </div>
  );
}
```

**Svelte:**

```svelte
<script lang="ts">
  import type { FontMetadata } from '$lib/types';

  export let font: FontMetadata;
  export let onClick: (font: FontMetadata) => void | undefined;
  export let size = 16;
  export let showLicense = false;
</script>

<div class="font-card" style:font-size="{size}px">
  <h3>{font.displayName}</h3>
  {#if showLicense}
    <LicenseInfo license={font.license} />
  {/if}
  {#if onClick}
    <button onclick={() => onClick(font)}>Select</button>
  {/if}
</div>
```

**Key Differences:**
- Props declared with `export let` instead of function parameters
- Default values assigned with `=` in declaration
- Event handlers use lowercase (`onclick`)
- Props passed as attributes without curly braces for simple values

---

#### Slot/Children Composition

**React:**

```tsx
// Modal.tsx
function Modal({ children, title, footer }: {
  children: React.ReactNode;
  title: string;
  footer?: React.ReactNode;
}) {
  return (
    <div className="modal">
      <header>{title}</header>
      <main>{children}</main>
      {footer && <footer>{footer}</footer>}
    </div>
  );
}

// Usage
<Modal title="Select Font" footer={<Button>Save</Button>}>
  <p>Choose a font from the list below.</p>
  <FontSelector />
</Modal>
```

**Svelte:**

```svelte
<!-- Modal.svelte -->
<script lang="ts">
  export let title: string;
  export let footer = false;
</script>

<div class="modal">
  <header>{title}</header>
  <main>
    <slot />
  </main>
  {#if footer}
    <footer>
      <slot name="footer" />
    </footer>
  {/if}
</div>

<!-- Usage -->
<Modal title="Select Font" footer>
  <svelte:fragment slot="footer">
    <Button>Save</Button>
  </svelte:fragment>
  <p>Choose a font from the list below.</p>
  <FontSelector />
</Modal>
```

**Key Differences:**
- Named slots using `slot="name"` and `<slot name="name" />`
- Multiple slots with different names
- Default slot uses `<slot />` without name
- `<svelte:fragment>` for content without wrapper element

---

### Common Patterns

#### Form Handling

**React:**

```tsx
function SearchForm({ onSearch }: { onSearch: (query: string) => void }) {
  const [query, setQuery] = useState('');

  const handleSubmit = (e: FormEvent) => {
    e.preventDefault();
    onSearch(query);
  };

  return (
    <form onSubmit={handleSubmit}>
      <input
        value={query}
        onChange={(e) => setQuery(e.target.value)}
        placeholder="Search fonts..."
      />
      <button type="submit">Search</button>
    </form>
  );
}
```

**Svelte:**

```svelte
<script lang="ts">
  export let onSearch: (query: string) => void;

  let query = $state('');

  function handleSubmit(e: Event) {
    e.preventDefault();
    onSearch(query);
  }
</script>

<form onsubmit={handleSubmit}>
  <input
    bind:value={query}
    placeholder="Search fonts..."
  />
  <button type="submit">Search</button>
</form>
```

**Key Difference:** Two-way binding with `bind:value` eliminates the need for `onChange`.

---

#### Lists with Keys

**React:**

```tsx
{fonts.map(font => (
  <FontCard
    key={font.id}
    font={font}
    onClick={() => handleSelect(font)}
  />
))}
```

**Svelte:**

```svelte
{#each fonts as font (font.id)}
  <FontCard
    {font}
    onClick={() => handleSelect(font)}
  />
{/each}
```

**Key Difference:** Key specified in parentheses after item name: `as item (key)`.

---

#### Lifecycle Methods

**React:**

```tsx
useEffect(() => {
  console.log('Mounted');
  return () => console.log('Cleanup');
}, []);

useEffect(() => {
  console.log('count changed:', count);
}, [count]);
```

**Svelte:**

```svelte
<script>
  import { onMount, onDestroy } from 'svelte';

  let count = $state(0);

  $effect(() => {
    console.log('count changed:', count);
  });

  onMount(() => {
    console.log('Mounted');
  });

  onDestroy(() => {
    console.log('Cleanup');
  });
</script>
```

---

## Scalability & Commercialization

### When to Add Backend

#### Indicators for Backend Implementation

| Metric | Threshold | Action |
|--------|-----------|--------|
| Daily Active Users | > 1,000 | Consider backend |
| Google Fonts API Usage | > 800/day (80% of limit) | Implement server proxy |
| Feature Requests | > 10/month for user accounts | Plan authentication |
| Comparison Saves | Users frequently export/save | Add database |
| Page Load Time | > 3s on mobile | Optimize with backend caching |

#### Backend Architecture (When Needed)

```
┌─────────────────────────────────────────────────────────────┐
│                        Vercel Edge                          │
│  ┌───────────────────────────────────────────────────────┐  │
│  │              SvelteKit Server Functions               │  │
│  │  ┌──────────────┐  ┌──────────────┐                  │  │
│  │  │ API Routes   │  │ Auth Routes  │                  │  │
│  │  └──────────────┘  └──────────────┘                  │  │
│  └───────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘
         │                       │
         ▼                       ▼
┌──────────────────┐   ┌──────────────────┐
│ Vercel Postgres  │   │  Vercel KV       │
│ (User accounts,  │   │  (Caching,      │
│  saved comps)    │   │   rate limiting) │
└──────────────────┘   └──────────────────┘
```

#### Recommended Backend Stack

| Component | Technology | Why |
|-----------|------------|-----|
| Server Runtime | Vercel Edge Functions | Fast, global, free tier generous |
| Database | Vercel Postgres (Neon) | Managed, edge-ready, TypeScript native |
| Caching | Vercel KV (Redis) | Fast key-value store, built-in |
| Authentication | Lucia Auth | Lightweight, framework-agnostic |
| ORM | Drizzle ORM | TypeScript-first, no runtime overhead |
| File Storage | Vercel Blob | Simple, scalable storage |

---

### Monetization Models

#### Tier 1: Freemium (Recommended Launch Model)

| Feature | Free | Pro ($5/mo) |
|---------|------|-------------|
| Font comparisons | 4 fonts max | Unlimited |
| Save comparisons | Browser storage only | Cloud sync |
| Export images | Watermarked | No watermark |
| Custom text | Limited chars | Unlimited |
| Advanced filters | Basic | Advanced |
| API access | ❌ | ✅ |

#### Tier 2: Team/Agency ($29/mo)

- All Pro features
- Team collaboration (shared workspaces)
- Brand management (save brand fonts)
- Custom domains for shared comparisons
- Priority support
- Monthly usage reports

#### Tier 3: Enterprise (Custom)

- Unlimited API access
- Self-hosted deployment option
- Custom integrations
- SSO authentication
- Dedicated support
- SLA guarantees

---

### Additional Features for Monetization

1. **Font Pairing Recommendations**
   - ML-based font matching
   - Designer-curated pairings
   - Upload custom fonts for analysis

2. **CSS Generator**
   - Export optimized CSS
   - Variable font support
   - Fallback font stacks

3. **Embeddable Widget**
   - Embed comparison on external sites
   - White-label options
   - Custom branding

4. **Font Inspector**
   - Detailed glyph analysis
   - Character set viewer
   - Font metrics display

5. **A/B Testing**
   - Test font combinations
   - User feedback collection
   - Conversion tracking

---

## Deployment

### Vercel Configuration

#### vercel.json

```json
{
  "buildCommand": "yarn build",
  "devCommand": "yarn dev",
  "installCommand": "yarn install",
  "framework": "sveltekit",
  "regions": ["iad1"],
  "headers": [
    {
      "source": "/(.*)",
      "headers": [
        {
          "key": "X-Content-Type-Options",
          "value": "nosniff"
        },
        {
          "key": "X-Frame-Options",
          "value": "DENY"
        },
        {
          "key": "X-XSS-Protection",
          "value": "1; mode=block"
        },
        {
          "key": "Referrer-Policy",
          "value": "strict-origin-when-cross-origin"
        }
      ]
    },
    {
      "source": "/static/(.*)",
      "headers": [
        {
          "key": "Cache-Control",
          "value": "public, max-age=31536000, immutable"
        }
      ]
    },
    {
      "source": "/fonts/(.*)",
      "headers": [
        {
          "key": "Cache-Control",
          "value": "public, max-age=604800"
        }
      ]
    }
  ],
  "rewrites": [
    {
      "source": "/api/:path*",
      "destination": "/api/:path*"
    }
  ]
}
```

---

### Environment Configuration

#### .env.example

```bash
# Google Fonts API Key
# Get from: https://developers.google.com/fonts/docs/developer_api
GOOGLE_FONTS_API_KEY=your_api_key_here

# Application Configuration
APP_URL=https://glyphdiff.com
APP_NAME=GlyphDiff

# Analytics (Optional)
VITE_GA_ID=G-XXXXXXXXXX
VITE_PLAUSIBLE_DOMAIN= glyphdiff.com

# Feature Flags
VITE_ENABLE_CACHE=true
VITE_ENABLE_ANALYTICS=false
```

#### vite.config.ts

```typescript
import { sveltekit } from '@sveltejs/kit/vite';
import { defineConfig } from 'vite';

export default defineConfig({
  plugins: [sveltekit()],
  define: {
    // Expose env variables to client code
    'import.meta.env.VITE_GOOGLE_FONTS_API_KEY': JSON.stringify(process.env.GOOGLE_FONTS_API_KEY),
  }
});
```

---

### DNS Configuration

#### DNS Records for glyphdiff.com

| Type | Name | Value | TTL |
|------|------|-------|-----|
| A | @ | 76.76.21.21 | 3600 |
| CNAME | www | cname.vercel-dns.com | 3600 |

**Note:** 76.76.21.21 is Vercel's IPv4 address for custom domains.

---

### Build and Deploy Commands

```bash
# Install dependencies
yarn install

# Run development server
yarn dev

# Build for production
yarn build

# Preview production build
yarn preview

# Run tests
yarn test

# Run linter
yarn lint

# Format code
yarn format

# Type check
yarn check
```

#### package.json Scripts

```json
{
  "name": "glyphdiff",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "dev": "vite dev",
    "build": "vite build",
    "preview": "vite preview",
    "check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
    "check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
    "lint": "oxlint",
    "format": "dprint fmt",
    "format:check": "dprint check",
    "test": "playwright test",
    "test:unit": "vitest"
  },
  "devDependencies": {
    "@sveltejs/adapter-vercel": "^5.0.0",
    "@sveltejs/kit": "^2.0.0",
    "svelte": "^5.0.0",
    "typescript": "^5.3.0",
    "vite": "^5.0.0"
  }
}
```

---

### Deployment Steps

1. **Push to GitHub**
   ```bash
   git init
   git add .
   git commit -m "Initial commit"
   git branch -M main
   git remote add origin git@github.com:your-username/glyphdiff.git
   git push -u origin main
   ```

2. **Connect to Vercel**
   - Go to [vercel.com](https://vercel.com)
   - Click "Add New Project"
   - Import from GitHub
   - Configure environment variables:
     - `GOOGLE_FONTS_API_KEY`

3. **Configure Custom Domain**
   - Go to Project Settings → Domains
   - Add `glyphdiff.com`
   - Add `www.glyphdiff.com`
   - Update DNS records as shown above

4. **Deploy**
   - Push changes to GitHub
   - Vercel automatically deploys on push to main
   - Preview deployments for pull requests

---

## Risk Assessment

### Technical Risks

| Risk | Probability | Impact | Mitigation |
|------|-------------|--------|------------|
| Google Fonts API rate limiting | Medium | High | Implement caching, batch requests, consider backend proxy |
| Browser font loading issues | Low | Medium | Use `document.fonts.load()`, implement fallback fonts |
| Poor mobile performance | Medium | High | Lazy loading, code splitting, test on real devices |
| Accessibility violations | Low | Medium | Regular audits with axe DevTools, keyboard testing |
| Vercel free tier limits | Low | Low | Monitor usage, easy upgrade path |

### Learning Curve Risks

| Risk | Probability | Impact | Mitigation |
|------|-------------|--------|------------|
| Difficulty with Svelte 5 runes | Medium | High | Start with simple components, practice with $state basics |
| TypeScript integration issues | Low | Medium | Use strict mode from start, leverage SvelteKit templates |
| CSS/Tailwind complexity | Low | Low | Use utility classes, avoid custom CSS where possible |
| Bits UI learning curve | Low | Medium | Read documentation, check examples, copy patterns |

### External Dependency Risks

| Risk | Probability | Impact | Mitigation |
|------|-------------|--------|------------|
| Google Fonts API changes | Low | High | Use TypeScript interfaces, watch for deprecation notices |
| Fontshare availability changes | Low | Low | Include as optional source, can be removed if needed |
| Vercel downtime | Very Low | Medium | Static files served from CDN, minimal impact |
| Bits UI breaking changes | Medium | Low | Lock to specific version, update carefully |

---

## Success Metrics

### Learning Success Metrics

| Metric | Target | Measurement |
|--------|--------|-------------|
| Svelte 5 proficiency | Comfortable with $state, $derived, $effect | Self-assessment quiz |
| SvelteKit understanding | Build 3+ routes with data loading | Route count |
| Store management | Implement 4 stores with persistence | Store count |
| Component library usage | Use 5+ Bits UI components | Component count |
| TypeScript adoption | 100% typed codebase | Lint check |

### Project Success Metrics

| Metric | Target | Measurement |
|--------|--------|-------------|
| Functional font catalog | 1000+ fonts loaded | Google Fonts API response |
| Comparison tool working | 4 fonts simultaneously | Manual testing |
| Performance score | 90+ Lighthouse score | Lighthouse audit |
| Mobile responsiveness | Pass on 375px - 1280px | Browser DevTools |
| Accessibility | WCAG 2.1 AA compliant | axe DevTools |

### Milestones

- [ ] **Week 1 Complete:** Environment setup, basic components, types defined
- [ ] **Week 2 Complete:** Font catalog with data fetching, routing working
- [ ] **Week 3 Complete:** All stores implemented, URL state working
- [ ] **Week 4 Complete:** Polished UI, dark mode, responsive design
- [ ] **MVP Launch:** Application deployed to glyphdiff.com
- [ ] **Post-Launch:** Collect feedback, iterate on features

---

## Appendix

### Commands Reference

#### Project Initialization

```bash
# Create new SvelteKit project
yarn create svelte@latest glyphdiff

# Select options:
# - Which Svelte app template? Skeleton project
# - Add type checking? Yes, using TypeScript
# - Select additional options: Playwright

# Navigate to project
cd glyphdiff

# Install dependencies
yarn install

# Add Tailwind CSS
yarn dlx svelte-add@latest tailwindcss

# Add Bits UI
yarn add bits-ui

# Install additional dependencies
yarn add clsx tailwind-merge

# Install oxlint and dprint
yarn add -D oxlint dprint
```

#### Development Commands

```bash
# Start development server
yarn dev

# Open browser to localhost:5173

# Type check
yarn check

# Type check in watch mode
yarn check:watch

# Lint code
yarn lint

# Format code
yarn format

# Run Playwright tests
yarn test

# Run unit tests (Vitest)
yarn test:unit
```

#### Build Commands

```bash
# Build for production
yarn build

# Preview production build
yarn preview

# Clean build artifacts
rm -rf .svelte-kit build
```

#### Git Commands

```bash
# Initialize git repo
git init

# Create .gitignore
echo ".svelte-kit
node_modules
.env
.DS_Store
dist
build
.vercel" > .gitignore

# Stage all files
git add .

# Commit
git commit -m "Initial commit"

# Create main branch
git branch -M main

# Add remote
git remote add origin git@github.com:username/glyphdiff.git

# Push to remote
git push -u origin main
```

---

### Learning Resources

#### Official Documentation

- [Svelte 5 Documentation](https://svelte-5-preview.vercel.app/)
- [SvelteKit Documentation](https://kit.svelte.dev/docs)
- [Tailwind CSS Documentation](https://tailwindcss.com/docs)
- [Bits UI Documentation](https://www.bits-ui.com/)

#### React to Svelte Migration

- [Svelte for React Developers](https://svelte.dev/docs/svelte-vs-react)
- [Svelte 5 Runes Guide](https://svelte-5-preview.vercel.app/docs/runes-api)
- [SvelteKit Data Loading](https://kit.svelte.dev/docs/load)

#### Google Fonts API

- [Google Fonts API Developer Guide](https://developers.google.com/fonts/docs/developer_api)
- [Google Fonts API Reference](https://developers.google.com/fonts/docs/reference/rest)

#### Video Resources

- [Svelte 5 Tutorial](https://www.youtube.com/results?search_query=svelte+5+tutorial)
- [SvelteKit Crash Course](https://www.youtube.com/results?search_query=sveltekit+crash+course)
- [Tailwind CSS Full Course](https://www.youtube.com/results?search_query=tailwind+css+full+course)

#### Community

- [Svelte Discord](https://svelte.dev/chat)
- [Svelte subreddit](https://reddit.com/r/sveltejs)
- [SvelteKit subreddit](https://reddit.com/r/sveltekit)

---

### File Templates

#### Component Template

```svelte
<script lang="ts">
  import type { Snippet } from 'svelte';

  export let prop: string;

  // State
  let count = $state(0);

  // Derived state
  let doubled = $derived(count * 2);

  // Actions
  function increment() {
    count += 1;
  }

  // Lifecycle
  import { onMount, onDestroy } from 'svelte';

  onMount(() => {
    console.log('Component mounted');
  });

  onDestroy(() => {
    console.log('Component destroyed');
  });
</script>

<div class="component">
  <h2>{prop}</h2>
  <p>Count: {count}, Doubled: {doubled}</p>
  <button onclick={increment}>Increment</button>
</div>

<style>
  .component {
    padding: 1rem;
  }
</style>
```

#### Store Template

```typescript
import type { FontMetadata } from '$lib/types';
import { setCache, getCache } from '$lib/utils/cache';

class ExampleStore {
  // State
  items = $state<FontMetadata[]>([]);
  loading = $state(false);
  error = $state<Error | null>(null);

  // Derived state (computed automatically)
  get count() {
    return this.items.length;
  }

  // Methods
  async loadItems() {
    this.loading = true;
    this.error = null;

    try {
      // Load from cache first
      const cached = getCache('items');
      if (cached) {
        this.items = cached;
        return;
      }

      // Fetch items
      // this.items = await fetchItems();
      // setCache('items', this.items);
    } catch (e) {
      this.error = e as Error;
    } finally {
      this.loading = false;
    }
  }

  addItem(item: FontMetadata) {
    this.items = [...this.items, item];
  }

  removeItem(id: string) {
    this.items = this.items.filter(item => item.id !== id);
  }
}

// Export singleton instance
export const exampleStore = new ExampleStore();
```

#### Load Function Template

```typescript
// +page.ts or +page.server.ts
import type { PageLoad } from './$types';

export const load: PageLoad = async ({ fetch, depends, url }) => {
  // Declare dependencies for invalidation
  depends('app:data');

  // Get URL parameters
  const search = url.searchParams.get('search') || '';

  try {
    // Fetch data
    const response = await fetch('/api/data');
    const data = await response.json();

    return {
      data,
      search
    };
  } catch (error) {
    return {
      data: [],
      search,
      error: error.message
    };
  }
};
```

---

### Troubleshooting

#### Common Issues

**Issue: Google Fonts API returns 403**

```bash
# Solution: Check API key and rate limits
# 1. Verify API key is correct
# 2. Check API key restrictions (set to None for testing)
# 3. Verify you haven't exceeded daily quota
```

**Issue: Tailwind classes not working**

```bash
# Solution: Check configuration
# 1. Ensure app.css imports tailwind directives
# 2. Restart dev server after config changes
# 3. Check vite.config.ts includes postcss config
```

**Issue: Svelte 5 syntax errors**

```bash
# Solution: Ensure you're using latest Svelte
npm install svelte@next

# If using VS Code, install Svelte extension
# Ensure it's the latest version for Svelte 5 support
```

**Issue: TypeScript errors with $state**

```bash
# Solution: Update Svelte configuration
# Ensure svelte.config.js includes:
export default {
  compilerOptions: {
    runes: true
  }
};
```

**Issue: Vercel deployment fails**

```bash
# Solution: Check build output
npm run build

# Review error logs in Vercel dashboard
# Common issues:
# - Missing environment variables
# - TypeScript errors
# - Build timeout
```

---

### Performance Checklist

- [ ] Implement lazy loading for fonts
- [ ] Use SvelteKit static generation where possible
- [ ] Optimize images (use webp format)
- [ ] Minimize JavaScript bundle size
- [ ] Use code splitting for routes
- [ ] Implement caching strategy
- [ ] Enable compression (handled by Vercel)
- [ ] Test Lighthouse scores
- [ ] Minimize layout shifts
- [ ] Use appropriate font formats (WOFF2)

---

## Conclusion

This project plan provides a comprehensive roadmap for building glyphdiff.com as a learning-focused MVP. The pure client-side approach prioritizes mastering Svelte 5 and SvelteKit while building a functional font comparison tool.

### Next Steps

1. Set up the development environment (Week 1 tasks)
2. Obtain Google Fonts API key
3. Configure environment variables
4. Begin implementing Svelte fundamentals

Good luck on your React → Svelte journey! 🚀

---

*Document Version: 1.0*
*Last Updated: December 2025*
*Project: glyphdiff.com*