chess/docs/analysis/feature-prioritization.md

# Feature Prioritization: HTML Chess Game

## Executive Summary
**Total Features Identified**: 47 features across 5 phases
**MVP Features**: 15 (must-have for playable game)
**Phase 2 Features**: 12 (enhanced experience)
**Phase 3 Features**: 10 (competitive product)
**Phase 4+ Features**: 10 (market differentiation)

---

## 1. Feature Prioritization Framework

### Evaluation Criteria:

| Criteria | Weight | Description |
|----------|--------|-------------|
| **User Value** | 35% | How much users benefit |
| **Technical Complexity** | 25% | Implementation effort |
| **Dependencies** | 20% | Blockers and prerequisites |
| **Market Differentiation** | 10% | Competitive advantage |
| **Risk Mitigation** | 10% | Reduces project risk |

### Priority Levels:

- **P0 (CRITICAL)**: Must have for MVP - game is unplayable without this
- **P1 (HIGH)**: Should have for MVP - significantly degrades experience without
- **P2 (MEDIUM)**: Could have - nice enhancement but not critical
- **P3 (LOW)**: Won't have initially - future consideration

---

## 2. MVP Features (Phase 1) - "Playable Chess Game"

**Timeline**: 4-6 weeks | **Effort**: 40-50 hours | **User Value**: 90%

### 2.1 Core Game Mechanics (P0 - CRITICAL)

#### F1: Chess Board Rendering
**Priority**: P0 | **Effort**: 8 hours | **Value**: Critical | **Score**: 95/100

**Description**: Display 8x8 chess board with alternating colors and coordinates.

**Acceptance Criteria**:
- 8x8 grid with light/dark squares
- Row numbers (1-8) and column letters (a-h)
- Responsive sizing (fills container)
- Clean visual design

**Dependencies**: None
**Blockers**: None

**Justification**: Absolutely essential - cannot play chess without a board.

---

#### F2: Piece Placement & Display
**Priority**: P0 | **Effort**: 6 hours | **Value**: Critical | **Score**: 95/100

**Description**: Render all 32 chess pieces in starting positions.

**Acceptance Criteria**:
- All 32 pieces visible (16 white, 16 black)
- Pieces distinguishable (King, Queen, Rook, Bishop, Knight, Pawn)
- SVG or high-quality Unicode rendering
- Pieces centered in squares

**Dependencies**: F1 (Board Rendering)
**Blockers**: None

**Justification**: Cannot play without pieces.

---

#### F3: Basic Move Execution
**Priority**: P0 | **Effort**: 4 hours | **Value**: Critical | **Score**: 90/100

**Description**: Allow players to select and move pieces via click.

**Acceptance Criteria**:
- Click piece to select
- Click destination to move
- Visual indication of selected piece
- Piece moves to new square

**Dependencies**: F1, F2
**Blockers**: None

**Justification**: Core interaction mechanism.

---

#### F4: Move Validation (Basic Pieces)
**Priority**: P0 | **Effort**: 12 hours | **Value**: Critical | **Score**: 95/100

**Description**: Validate moves for King, Queen, Rook, Bishop, Knight according to chess rules.

**Acceptance Criteria**:
- King moves 1 square any direction
- Queen moves any number of squares in straight/diagonal lines
- Rook moves any number of squares in straight lines
- Bishop moves any number of squares diagonally
- Knight moves in L-shape
- Cannot move to square occupied by own piece
- Cannot jump over pieces (except knight)

**Dependencies**: F3
**Blockers**: None

**Justification**: Game is broken if pieces move incorrectly.

---

#### F5: Pawn Move Validation
**Priority**: P0 | **Effort**: 6 hours | **Value**: Critical | **Score**: 90/100

**Description**: Implement pawn movement rules including promotion.

**Acceptance Criteria**:
- Move 1 square forward (if not blocked)
- Move 2 squares forward from starting position
- Capture diagonally forward
- Promote to Queen/Rook/Bishop/Knight when reaching rank 8/1
- Cannot move backward

**Dependencies**: F4
**Blockers**: None

**Justification**: Pawn is unique and essential piece.

---

#### F6: Turn Management
**Priority**: P0 | **Effort**: 3 hours | **Value**: Critical | **Score**: 85/100

**Description**: Enforce turn-based gameplay (white moves first, then black, alternating).

**Acceptance Criteria**:
- White moves first
- Players alternate turns
- Cannot move opponent's pieces
- Visual indication of whose turn it is

**Dependencies**: F3
**Blockers**: None

**Justification**: Fundamental to chess rules.

---

#### F7: Capture Mechanics
**Priority**: P0 | **Effort**: 4 hours | **Value**: Critical | **Score**: 90/100

**Description**: Allow pieces to capture opponent pieces.

**Acceptance Criteria**:
- Moving to square with opponent piece captures it
- Captured piece removed from board
- Captured pieces displayed separately (optional but nice)
- Cannot capture own pieces

**Dependencies**: F4, F5
**Blockers**: None

**Justification**: Cannot win without capturing.

---

#### F8: Check Detection
**Priority**: P0 | **Effort**: 8 hours | **Value**: Critical | **Score**: 95/100

**Description**: Detect when king is under attack (in check).

**Acceptance Criteria**:
- Identify when king is threatened
- Visual indication (highlight king in red)
- Display "Check!" message
- Cannot make move that leaves own king in check

**Dependencies**: F4, F5, F7
**Blockers**: None

**Justification**: Core chess rule - king cannot remain in check.

---

#### F9: Checkmate Detection
**Priority**: P0 | **Effort**: 8 hours | **Value**: Critical | **Score**: 95/100

**Description**: Detect when game is over (checkmate).

**Acceptance Criteria**:
- Identify when king is in check AND no legal moves exist
- Display "Checkmate! [Color] wins!" message
- Prevent further moves after checkmate
- Highlight winning/losing position

**Dependencies**: F8
**Blockers**: None

**Justification**: Game cannot end properly without this.

---

#### F10: Stalemate Detection
**Priority**: P0 | **Effort**: 4 hours | **Value**: High | **Score**: 80/100

**Description**: Detect when game is drawn (stalemate).

**Acceptance Criteria**:
- Identify when player not in check but has no legal moves
- Display "Stalemate! Draw!" message
- End game properly

**Dependencies**: F8, F9
**Blockers**: None

**Justification**: Prevents incorrect wins/losses.

---

### 2.2 Essential UI Features (P0 - CRITICAL)

#### F11: New Game Button
**Priority**: P0 | **Effort**: 2 hours | **Value**: High | **Score**: 75/100

**Description**: Reset board to starting position.

**Acceptance Criteria**:
- Button clearly labeled "New Game"
- Resets board to initial state
- Confirmation dialog if game in progress
- Resets turn to white

**Dependencies**: None
**Blockers**: None

**Justification**: Must be able to start new games.

---

#### F12: Undo Move
**Priority**: P1 | **Effort**: 5 hours | **Value**: High | **Score**: 70/100

**Description**: Take back last move.

**Acceptance Criteria**:
- Undo button clearly visible
- Restores previous board state
- Reverses captures
- Can undo multiple moves
- Disabled at game start

**Dependencies**: F3 (Move history tracking)
**Blockers**: None

**Justification**: Critical for learning and correcting mistakes.

---

#### F13: Move Highlighting
**Priority**: P1 | **Effort**: 4 hours | **Value**: High | **Score**: 75/100

**Description**: Show last move made for clarity.

**Acceptance Criteria**:
- Highlight source and destination squares
- Different color than selection highlight
- Updates after each move
- Clear visual distinction

**Dependencies**: F3
**Blockers**: None

**Justification**: Essential for tracking game flow.

---

#### F14: Legal Move Indicators
**Priority**: P1 | **Effort**: 5 hours | **Value**: High | **Score**: 80/100

**Description**: Show where selected piece can move.

**Acceptance Criteria**:
- Display dots/highlights on legal squares
- Update when piece selected
- Clear when piece deselected
- Different visual for captures vs moves

**Dependencies**: F4, F5
**Blockers**: None

**Justification**: Greatly improves user experience and learning.

---

#### F15: Game Status Display
**Priority**: P0 | **Effort**: 3 hours | **Value**: Medium | **Score**: 70/100

**Description**: Show current game state (turn, check, checkmate, etc.).

**Acceptance Criteria**:
- "White to move" / "Black to move"
- "Check!" when in check
- "Checkmate!" when game over
- "Stalemate!" for draws
- Clearly visible and readable

**Dependencies**: F6, F8, F9, F10
**Blockers**: None

**Justification**: Players need to know game state.

---

## 3. Phase 2 Features - "Enhanced Experience"

**Timeline**: 2-3 weeks | **Effort**: 25-35 hours | **User Value**: 20% additional

### 3.1 Advanced Move Rules (P1 - HIGH)

#### F16: Castling
**Priority**: P1 | **Effort**: 8 hours | **Value**: High | **Score**: 75/100

**Description**: Implement castling (kingside and queenside).

**Acceptance Criteria**:
- King and rook haven't moved
- No pieces between king and rook
- King not in check, doesn't pass through check, doesn't end in check
- King moves 2 squares, rook jumps over
- Works for both sides

**Dependencies**: F4 (Move history required)
**Blockers**: None

**Justification**: Important strategic move, frequently used.

**Deferrable**: Yes - game playable without, but diminishes strategic depth.

---

#### F17: En Passant
**Priority**: P1 | **Effort**: 6 hours | **Value**: Medium | **Score**: 65/100

**Description**: Implement en passant capture for pawns.

**Acceptance Criteria**:
- Works only immediately after opponent pawn moves 2 squares
- Pawn captures as if opponent moved 1 square
- Removes captured pawn correctly
- Only available for one move

**Dependencies**: F5 (Pawn moves, move history)
**Blockers**: None

**Justification**: Completes chess rules, but rare in practice.

**Deferrable**: Yes - 95% of games don't use this.

---

### 3.2 UI Enhancements (P1 - HIGH)

#### F18: Drag and Drop
**Priority**: P1 | **Effort**: 8 hours | **Value**: High | **Score**: 70/100

**Description**: Allow dragging pieces instead of click-to-select.

**Acceptance Criteria**:
- Click and hold to drag piece
- Visual preview during drag
- Snap to square on drop
- Cancel on drag outside board
- Works on desktop and mobile

**Dependencies**: F3
**Blockers**: None

**Justification**: Intuitive interaction, expected by users.

**Deferrable**: Yes - click-to-select works, but less polished.

---

#### F19: Move Animations
**Priority**: P2 | **Effort**: 6 hours | **Value**: Medium | **Score**: 60/100

**Description**: Smooth piece movement animations.

**Acceptance Criteria**:
- Pieces glide to destination (300ms)
- 60fps animation
- Optional (can disable in settings)
- Doesn't block UI

**Dependencies**: F3
**Blockers**: None

**Justification**: Polish feature, improves feel but not function.

**Deferrable**: Yes - instant moves are functional.

---

#### F20: Move History List
**Priority**: P1 | **Effort**: 6 hours | **Value**: Medium-High | **Score**: 68/100

**Description**: Display list of moves in algebraic notation.

**Acceptance Criteria**:
- Show all moves in chronological order
- Algebraic notation (e4, Nf3, O-O, etc.)
- Click move to jump to that position
- Highlight current move
- Scrollable list

**Dependencies**: F3
**Blockers**: None

**Justification**: Useful for reviewing game, standard in chess apps.

**Deferrable**: Yes - can play without, but diminishes experience.

---

#### F21: Board Themes
**Priority**: P2 | **Effort**: 4 hours | **Value**: Low-Medium | **Score**: 50/100

**Description**: Multiple color schemes for board.

**Acceptance Criteria**:
- 3+ themes (Classic brown, Blue, Green, etc.)
- Easy to switch in settings
- Persists across sessions
- High contrast for accessibility

**Dependencies**: F1
**Blockers**: None

**Justification**: Personalization, accessibility, but purely aesthetic.

**Deferrable**: Yes - nice to have, not essential.

---

#### F22: Piece Set Selection
**Priority**: P2 | **Effort**: 3 hours | **Value**: Low | **Score**: 45/100

**Description**: Multiple piece designs.

**Acceptance Criteria**:
- 2+ piece sets (Classic, Modern, etc.)
- Clearly distinguishable
- Settings toggle

**Dependencies**: F2
**Blockers**: None

**Justification**: Personalization only.

**Deferrable**: Yes - can ship with one set.

---

#### F23: Sound Effects
**Priority**: P2 | **Effort**: 4 hours | **Value**: Medium | **Score**: 55/100

**Description**: Audio feedback for moves, captures, check.

**Acceptance Criteria**:
- Move sound
- Capture sound
- Check sound
- Checkmate sound
- Mute toggle
- Not annoying

**Dependencies**: F3, F7, F8
**Blockers**: None

**Justification**: Enhances feel but not essential.

**Deferrable**: Yes - functional without sound.

---

#### F24: Flip Board Button
**Priority**: P2 | **Effort**: 2 hours | **Value**: Medium | **Score**: 55/100

**Description**: Rotate board 180 degrees.

**Acceptance Criteria**:
- Button to flip perspective
- Smooth animation (optional)
- Useful for over-the-board play
- Doesn't affect game state

**Dependencies**: F1
**Blockers**: None

**Justification**: Nice for two players on one device.

**Deferrable**: Yes - can manually view from other side.

---

### 3.3 Draw Conditions (P2 - MEDIUM)

#### F25: Insufficient Material Draw
**Priority**: P2 | **Effort**: 3 hours | **Value**: Medium | **Score**: 60/100

**Description**: Detect automatic draw (e.g., K vs K, K+B vs K).

**Acceptance Criteria**:
- King vs King
- King + Bishop vs King
- King + Knight vs King
- Display "Draw - Insufficient Material"

**Dependencies**: F9, F10
**Blockers**: None

**Justification**: Proper rule enforcement, but rare.

**Deferrable**: Yes - players can agree to draw.

---

#### F26: Three-Fold Repetition
**Priority**: P2 | **Effort**: 6 hours | **Value**: Low-Medium | **Score**: 50/100

**Description**: Detect when same position occurs 3 times.

**Acceptance Criteria**:
- Track position hashes
- Detect repetition
- Offer draw (not automatic)
- Display "Draw available (repetition)"

**Dependencies**: F3 (Move history)
**Blockers**: None

**Justification**: Proper rules, but rare and complex.

**Deferrable**: Yes - rare in casual games.

---

#### F27: 50-Move Rule
**Priority**: P2 | **Effort**: 4 hours | **Value**: Low | **Score**: 45/100

**Description**: Draw if 50 moves without capture or pawn move.

**Acceptance Criteria**:
- Track move count
- Reset on captures/pawn moves
- Offer draw at 50 moves
- Display "Draw available (50-move rule)"

**Dependencies**: F3, F5, F7
**Blockers**: None

**Justification**: Complete rules, but very rare.

**Deferrable**: Yes - unlikely in most games.

---

## 4. Phase 3 Features - "AI & Competition"

**Timeline**: 3-4 weeks | **Effort**: 30-40 hours | **User Value**: 25% additional

### 4.1 AI Opponent (P1 - HIGH)

#### F28: Basic AI (Easy Difficulty)
**Priority**: P1 | **Effort**: 15 hours | **Value**: Very High | **Score**: 85/100

**Description**: Computer opponent with beginner-level play.

**Acceptance Criteria**:
- Minimax algorithm depth 3-4
- Makes legal moves
- Response time < 1s
- Beatable by beginners
- Some random moves for variety

**Dependencies**: All Phase 1 features
**Blockers**: None

**Justification**: **Major feature** - enables single-player mode.

**Deferrable**: Only if targeting two-player only initially.

---

#### F29: Intermediate AI
**Priority**: P2 | **Effort**: 8 hours | **Value**: High | **Score**: 75/100

**Description**: More challenging AI opponent.

**Acceptance Criteria**:
- Minimax depth 5-6
- Alpha-beta pruning
- Better position evaluation
- Response time < 2s
- Challenging for casual players

**Dependencies**: F28
**Blockers**: None

**Justification**: Expands user base to intermediate players.

**Deferrable**: Yes - can ship with easy AI first.

---

#### F30: Hard AI
**Priority**: P3 | **Effort**: 12 hours | **Value**: Medium | **Score**: 60/100

**Description**: Expert-level AI opponent.

**Acceptance Criteria**:
- Minimax depth 7+
- Transposition tables
- Opening book
- Response time < 5s
- Very challenging

**Dependencies**: F29
**Blockers**: None

**Justification**: Nice for advanced players, but niche.

**Deferrable**: Yes - most users won't need this.

---

#### F31: Difficulty Selector
**Priority**: P1 | **Effort**: 2 hours | **Value**: High | **Score**: 70/100

**Description**: UI to choose AI difficulty.

**Acceptance Criteria**:
- Easy/Medium/Hard buttons
- Visual indication of current level
- Can change between games
- Default to Easy

**Dependencies**: F28, F29
**Blockers**: None

**Justification**: Essential if multiple AI levels exist.

**Deferrable**: No - if AI feature is present.

---

### 4.2 Game Management (P2 - MEDIUM)

#### F32: Player Name Entry
**Priority**: P2 | **Effort**: 2 hours | **Value**: Low-Medium | **Score**: 50/100

**Description**: Allow players to enter names.

**Acceptance Criteria**:
- Input fields for white/black names
- Display in game UI
- Persists during session
- Default to "White" / "Black"

**Dependencies**: None
**Blockers**: None

**Justification**: Personalization, but low priority.

**Deferrable**: Yes.

---

#### F33: Game Save/Load
**Priority**: P2 | **Effort**: 6 hours | **Value**: Medium | **Score**: 60/100

**Description**: Save game to resume later.

**Acceptance Criteria**:
- Save current position to localStorage
- Load saved game
- Multiple save slots (optional)
- Auto-save on close (optional)

**Dependencies**: F3 (Game state)
**Blockers**: None

**Justification**: Useful for long games, but can play in one session.

**Deferrable**: Yes.

---

#### F34: PGN Export
**Priority**: P2 | **Effort**: 5 hours | **Value**: Medium-High | **Score**: 65/100

**Description**: Export game in standard PGN format.

**Acceptance Criteria**:
- Generate valid PGN
- Download as .pgn file
- Include metadata (players, date, result)
- Can import into other chess software

**Dependencies**: F20 (Move history)
**Blockers**: None

**Justification**: Useful for analysis and sharing.

**Deferrable**: Yes - can copy move list manually.

---

#### F35: PGN Import
**Priority**: P2 | **Effort**: 6 hours | **Value**: Medium | **Score**: 60/100

**Description**: Load game from PGN file.

**Acceptance Criteria**:
- Parse PGN format
- Load position and move history
- Handle variations (optional)
- Validate PGN syntax

**Dependencies**: F34
**Blockers**: None

**Justification**: Nice for replaying famous games.

**Deferrable**: Yes - niche feature.

---

#### F36: Resign Button
**Priority**: P2 | **Effort**: 1 hour | **Value**: Low-Medium | **Score**: 50/100

**Description**: Allow player to concede.

**Acceptance Criteria**:
- "Resign" button
- Confirmation dialog
- Ends game correctly
- Display "[Color] resigned"

**Dependencies**: F9 (Game end logic)
**Blockers**: None

**Justification**: Proper etiquette, but can just start new game.

**Deferrable**: Yes.

---

#### F37: Offer Draw Button
**Priority**: P2 | **Effort**: 2 hours | **Value**: Low | **Score**: 45/100

**Description**: Propose draw to opponent.

**Acceptance Criteria**:
- "Offer Draw" button
- Opponent can accept/decline
- Ends game if accepted
- Display "Draw by agreement"

**Dependencies**: F10 (Draw logic)
**Blockers**: None

**Justification**: Etiquette feature, low priority.

**Deferrable**: Yes.

---

## 5. Phase 4 Features - "Advanced & Analytics"

**Timeline**: 2-3 weeks | **Effort**: 20-30 hours | **User Value**: 10% additional

### 5.1 Time Controls (P2 - MEDIUM)

#### F38: Move Timer
**Priority**: P2 | **Effort**: 6 hours | **Value**: Medium | **Score**: 60/100

**Description**: Count time per move.

**Acceptance Criteria**:
- Display time for current move
- Pause when not player's turn
- Reset on move
- Visual countdown

**Dependencies**: F6 (Turn management)
**Blockers**: None

**Justification**: Adds urgency, but not standard for casual play.

**Deferrable**: Yes.

---

#### F39: Game Timer (Chess Clock)
**Priority**: P2 | **Effort**: 8 hours | **Value**: Medium-High | **Score**: 65/100

**Description**: Chess clock with time controls (5+3, 10+0, etc.).

**Acceptance Criteria**:
- Configurable time (5min, 10min, 15min, etc.)
- Optional increment per move
- Time runs down during turn
- Lose on timeout
- Pause/resume

**Dependencies**: F38
**Blockers**: None

**Justification**: Popular in online chess, adds competitive element.

**Deferrable**: Yes - casual games don't need time limits.

---

### 5.2 Analysis Features (P3 - LOW)

#### F40: Move Hints
**Priority**: P3 | **Effort**: 5 hours | **Value**: Medium | **Score**: 55/100

**Description**: AI suggests best move.

**Acceptance Criteria**:
- "Hint" button
- Highlights recommended move
- Doesn't auto-play
- Can toggle on/off
- Limited uses (optional)

**Dependencies**: F28 (AI engine)
**Blockers**: None

**Justification**: Helpful for learning, but can make game too easy.

**Deferrable**: Yes.

---

#### F41: Move Evaluation Bar
**Priority**: P3 | **Effort**: 4 hours | **Value**: Medium | **Score**: 50/100

**Description**: Show position evaluation (+2.5 for white, etc.).

**Acceptance Criteria**:
- Vertical bar showing advantage
- Updates after each move
- Positive = white advantage, negative = black
- Optional (can hide)

**Dependencies**: F28 (Evaluation function)
**Blockers**: None

**Justification**: Advanced feature, intimidating for beginners.

**Deferrable**: Yes - analysis feature, not core gameplay.

---

#### F42: Move Annotations
**Priority**: P3 | **Effort**: 5 hours | **Value**: Low-Medium | **Score**: 45/100

**Description**: Mark moves as brilliant (!), good, mistake (?), blunder (??).

**Acceptance Criteria**:
- Analyze moves after game
- Display symbols in move list
- Explain why (optional)
- Export in PGN

**Dependencies**: F20, F28
**Blockers**: None

**Justification**: Post-game analysis, not needed during play.

**Deferrable**: Yes.

---

## 6. Phase 5+ Features - "Market Differentiation"

**Timeline**: Future releases | **Effort**: 50+ hours | **User Value**: Variable

### 6.1 Online Features (P3 - FUTURE)

#### F43: Online Multiplayer
**Priority**: P3 | **Effort**: 40+ hours | **Value**: Very High | **Score**: 70/100

**Description**: Play against other humans online.

**Acceptance Criteria**:
- WebSocket real-time communication
- Matchmaking system
- Handle disconnections
- Reconnect to games
- Spectator mode (optional)

**Dependencies**: Backend server, user accounts
**Blockers**: Requires significant backend infrastructure

**Justification**: **Massive feature** - completely changes scope. Essentially a different product.

**Deferrable**: Yes - focus on single-device multiplayer first.

---

#### F44: User Accounts
**Priority**: P3 | **Effort**: 20+ hours | **Value**: Medium | **Score**: 55/100

**Description**: Sign up, login, save progress.

**Acceptance Criteria**:
- Registration/login
- Password reset
- Profile page
- Game history saved to account
- OAuth (optional)

**Dependencies**: Backend server, database
**Blockers**: Requires backend infrastructure

**Justification**: Needed for online features, but not for local play.

**Deferrable**: Yes - localStorage sufficient for local games.

---

#### F45: ELO Rating System
**Priority**: P3 | **Effort**: 10 hours | **Value**: Medium | **Score**: 50/100

**Description**: Track player skill rating.

**Acceptance Criteria**:
- Calculate ELO after each game
- Display rating
- Matchmaking based on rating
- Rating history

**Dependencies**: F43, F44
**Blockers**: Only meaningful with online play

**Justification**: Competitive feature for online play only.

**Deferrable**: Yes.

---

### 6.2 Learning Features (P3 - FUTURE)

#### F46: Puzzle Mode
**Priority**: P3 | **Effort**: 15 hours | **Value**: High | **Score**: 65/100

**Description**: Tactical puzzles to solve.

**Acceptance Criteria**:
- Database of puzzles
- "Find the best move" challenge
- Feedback on solution
- Difficulty levels
- Progress tracking

**Dependencies**: Puzzle database
**Blockers**: Requires content creation

**Justification**: Great for learning, but separate from core game.

**Deferrable**: Yes - different product mode.

---

#### F47: Opening Explorer
**Priority**: P3 | **Effort**: 12 hours | **Value**: Medium | **Score**: 50/100

**Description**: Show common opening moves and statistics.

**Acceptance Criteria**:
- Display opening name
- Show popular continuations
- Win/loss statistics
- Master games database (optional)

**Dependencies**: Opening database
**Blockers**: Requires large dataset

**Justification**: Advanced feature for serious players.

**Deferrable**: Yes - niche audience.

---

## 7. Feature Priority Summary

### By Phase:

| Phase | Features | Effort (hours) | User Value | Cumulative Users |
|-------|---------|----------------|-----------|------------------|
| **Phase 1 (MVP)** | 15 | 40-50 | 90% | 60% satisfied |
| **Phase 2 (Enhanced)** | 12 | 25-35 | +20% | 85% satisfied |
| **Phase 3 (AI)** | 10 | 30-40 | +25% | 95% satisfied |
| **Phase 4 (Advanced)** | 6 | 20-30 | +10% | 98% satisfied |
| **Phase 5+ (Future)** | 4 | 50+ | Variable | Market expansion |

### By Priority:

| Priority | Count | Total Effort | Description |
|----------|-------|-------------|-------------|
| **P0 (CRITICAL)** | 13 | 55-65 hours | Unplayable without |
| **P1 (HIGH)** | 12 | 45-55 hours | Significantly degrades UX |
| **P2 (MEDIUM)** | 16 | 60-75 hours | Nice enhancements |
| **P3 (LOW)** | 6 | 80-100 hours | Future consideration |

---

## 8. Recommended Roadmap

### Milestone 1: Playable Game (Week 4-6)
**Features**: F1-F15 (MVP)
**Deliverable**: Two-player chess game with all rules
**Success Metric**: Can play complete game end-to-end

### Milestone 2: Polished Experience (Week 8-10)
**Features**: F16-F27 (Enhanced)
**Deliverable**: Smooth UI, special moves, draw conditions
**Success Metric**: 90% user satisfaction, no major UX complaints

### Milestone 3: AI Opponent (Week 11-14)
**Features**: F28-F37 (AI & Management)
**Deliverable**: Single-player mode with difficulty levels
**Success Metric**: 80% of users engage with AI mode

### Milestone 4: Competitive Features (Week 15-17)
**Features**: F38-F42 (Time controls, Analysis)
**Deliverable**: Timer modes, analysis tools
**Success Metric**: 50% of users try timer mode

### Milestone 5: Future Expansion (TBD)
**Features**: F43-F47 (Online, Learning)
**Deliverable**: Online multiplayer, puzzles, ratings
**Success Metric**: Market differentiation, user retention

---

## 9. Feature Cut Recommendations

### If Timeline is Tight, CUT First:

1. **F27: 50-Move Rule** (4 hours saved) - Extremely rare
2. **F26: Three-Fold Repetition** (6 hours) - Rare and complex
3. **F22: Piece Set Selection** (3 hours) - Pure aesthetics
4. **F23: Sound Effects** (4 hours) - Nice but not essential
5. **F37: Offer Draw** (2 hours) - Can just resign instead
6. **F36: Resign Button** (1 hour) - Can start new game
7. **F25: Insufficient Material Draw** (3 hours) - Obvious to players

**Total Time Saved**: 23 hours (reduces Phase 2 from 35 to 12 hours)

### If Targeting MVP Only:

**Include**: F1-F10 (Core mechanics + Checkmate/Stalemate)
**Defer**: F11-F15 to Phase 2 if absolutely necessary
**Result**: 45-hour MVP instead of 55-hour MVP

---

## 10. Feature Expansion Strategy

### User-Driven Prioritization:

After launching MVP, collect data on:
1. Most requested features (user feedback)
2. Most used features (analytics)
3. Drop-off points (where users quit)
4. Competitive gaps (what competitors have)

### A/B Testing Candidates:

- **F18: Drag-and-drop vs click-to-select** - Which do users prefer?
- **F19: Animations on/off by default** - Impact on engagement?
- **F21: Board themes** - Do users customize or use default?
- **F23: Sound effects** - Increase/decrease session length?

---

## 11. Market Positioning Matrix

### Feature Comparison with Competitors:

| Feature | Our MVP | Lichess | Chess.com | Market Importance |
|---------|---------|---------|-----------|------------------|
| Two-player local | ✅ | ✅ | ✅ | Critical |
| AI opponent | 🔲 Phase 3 | ✅ | ✅ | Very High |
| Online multiplayer | ❌ Future | ✅ | ✅ | High |
| Move analysis | 🔲 Phase 4 | ✅ | ✅ (Premium) | Medium |
| Puzzles | ❌ Future | ✅ | ✅ | Medium |
| Mobile app | ❌ Future | ✅ | ✅ | High |
| **Simple HTML game** | ✅ | ❌ | ❌ | **Our Niche** |

### Positioning:
- **Lichess/Chess.com**: Full-featured online platforms
- **Our Product**: Lightweight, no-account, local-first chess game

**Competitive Advantage**: Simplicity, privacy, offline play, no registration required.

---

## 12. Success Metrics by Phase

### Phase 1 (MVP):
- [ ] 100% of chess rules implemented correctly
- [ ] 0 game-breaking bugs in testing
- [ ] <2s load time
- [ ] Can complete full game in <5 minutes

### Phase 2 (Enhanced):
- [ ] 90% user satisfaction score
- [ ] <3 UI/UX complaints per 100 users
- [ ] 60fps on desktop, 30fps on mobile
- [ ] 50% of users try drag-and-drop

### Phase 3 (AI):
- [ ] AI responds in <1s (easy), <2s (medium)
- [ ] 70% of users play vs AI at least once
- [ ] 30% play multiple AI games
- [ ] AI difficulty progression feels smooth

### Phase 4 (Advanced):
- [ ] 20% of users try time controls
- [ ] 10% use analysis features
- [ ] 5% export PGN
- [ ] Power users play 10+ games

---

## Conclusion

**Recommended Strategy**:
1. **Ship MVP (Phase 1) fast** - 4-6 weeks, 15 features, 90% user value
2. **Validate with users** - Get feedback, measure engagement
3. **Iterate on Phase 2** - Add polish based on feedback
4. **Build AI (Phase 3)** - Major value add for single players
5. **Evaluate Phase 4+** - Data-driven decisions on advanced features

**Key Insight**:
- 15 features (Phase 1) = 90% of user value
- 27 features (Phases 1-2) = 95% of user value
- Diminishing returns after Phase 3

**Focus on nailing the core experience** rather than feature bloat. Simple, fast, correct chess is better than complex, slow, buggy chess.

**Don't build online multiplayer unless validated** - it's a 3-5x scope increase and changes the entire product.