diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..78c34df
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,187 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+**CalChat** is a calendar mobile app with AI support. The core concept is creating calendar events through a chat interface with an AI chatbot (Claude). Users can add, edit, and delete events via natural language conversation.
+
+This is a fullstack TypeScript monorepo with npm workspaces.
+
+## Commands
+
+### Root (monorepo)
+```bash
+npm install          # Install all dependencies for all workspaces
+```
+
+### Client (apps/client) - Expo React Native app
+```bash
+npm run start -w @caldav/client        # Start Expo dev server
+npm run android -w @caldav/client      # Start on Android
+npm run ios -w @caldav/client          # Start on iOS
+npm run web -w @caldav/client          # Start web version
+npm run lint -w @caldav/client         # Run ESLint
+```
+
+### Server (apps/server) - Express.js backend
+```bash
+npm run dev -w @caldav/server          # Start dev server with hot reload (tsx watch)
+npm run build -w @caldav/server        # Compile TypeScript
+npm run start -w @caldav/server        # Run compiled server (port 3000)
+```
+
+## Technology Stack
+
+| Area | Technology | Purpose |
+|------|------------|---------|
+| Frontend | React Native | Mobile UI Framework |
+| | Expo | Development platform |
+| | Expo-Router | File-based routing |
+| | NativeWind | Tailwind CSS for React Native |
+| Backend | Express.js | Web framework |
+| | MongoDB | Database |
+| | Mongoose | ODM |
+| | Claude (Anthropic) | AI/LLM for chat |
+| | JWT | Authentication |
+| Planned | iCalendar | Event export/import |
+
+## Architecture
+
+### Workspace Structure
+```
+apps/client      - @caldav/client - Expo React Native app
+apps/server      - @caldav/server - Express.js backend
+packages/shared  - @caldav/shared - Shared TypeScript types and models
+```
+
+### Frontend Architecture (apps/client)
+
+**Screens** (`src/app/`): Login, Register, Calendar, Chat, Event Detail, Notes - file-based routing via Expo-Router
+
+**Services**: API Client for HTTP requests, plus AuthService, EventService, ChatService for domain logic
+
+**Components**: Reusable UI (EventCard, ChatBubble, EventConfirmDialog, MonthSelector)
+
+**Stores**: AuthStore (user + token), EventsStore (calendar events)
+
+### Backend Architecture (apps/server)
+
+```
+src/
+├── app.ts                    # Entry point, DI setup, Express config
+├── controllers/              # Request handlers
+│   ├── AuthController.ts     # login(), register(), refresh(), logout()
+│   ├── ChatController.ts     # sendMessage(), confirmEvent(), rejectEvent(), getConversations(), getConversation()
+│   └── EventController.ts    # create(), getById(), getAll(), getByDateRange(), update(), delete()
+├── middleware/
+│   └── AuthMiddleware.ts     # authenticate() - JWT validation
+├── routes/                   # API endpoint definitions
+│   ├── index.ts              # Combines all routes under /api
+│   ├── auth.routes.ts        # /api/auth/*
+│   ├── chat.routes.ts        # /api/chat/* (protected)
+│   └── event.routes.ts       # /api/events/* (protected)
+├── services/                 # Business logic
+│   ├── interfaces/           # DB-agnostic interfaces (for dependency injection)
+│   │   ├── AIProvider.ts     # processMessage()
+│   │   ├── UserRepository.ts # + CreateUserData (server-internal DTO)
+│   │   ├── EventRepository.ts
+│   │   └── ChatRepository.ts
+│   ├── AuthService.ts
+│   ├── ChatService.ts
+│   └── EventService.ts
+├── repositories/             # Data access (DB-specific implementations)
+│   ├── index.ts              # Re-exports from ./mongo
+│   └── mongo/                # MongoDB implementation
+│       ├── models/           # Mongoose schemas
+│       │   ├── UserModel.ts
+│       │   ├── EventModel.ts
+│       │   └── ChatModel.ts
+│       ├── MongoUserRepository.ts
+│       ├── MongoEventRepository.ts
+│       └── MongoChatRepository.ts
+├── ai/
+│   └── ClaudeAdapter.ts      # Implements AIProvider
+└── utils/
+    ├── jwt.ts                # signToken(), verifyToken()
+    └── password.ts           # hash(), compare()
+```
+
+**API Endpoints:**
+- `POST /api/auth/login` - User login
+- `POST /api/auth/register` - User registration
+- `POST /api/auth/refresh` - Refresh JWT token
+- `POST /api/auth/logout` - User logout
+- `GET /api/events` - Get all events (protected)
+- `GET /api/events/range` - Get events by date range (protected)
+- `GET /api/events/:id` - Get single event (protected)
+- `POST /api/events` - Create event (protected)
+- `PUT /api/events/:id` - Update event (protected)
+- `DELETE /api/events/:id` - Delete event (protected)
+- `POST /api/chat/message` - Send message to AI (protected)
+- `POST /api/chat/confirm/:conversationId/:messageId` - Confirm proposed event (protected)
+- `POST /api/chat/reject/:conversationId/:messageId` - Reject proposed event (protected)
+- `GET /api/chat/conversations` - Get all conversations (protected)
+- `GET /api/chat/conversations/:id` - Get messages of a conversation with cursor-based pagination (protected)
+- `GET /health` - Health check
+
+### Shared Package (packages/shared)
+
+```
+src/
+├── index.ts
+└── models/
+    ├── index.ts
+    ├── User.ts           # User, CreateUserDTO, LoginDTO, AuthResponse
+    ├── CalendarEvent.ts  # CalendarEvent, CreateEventDTO, UpdateEventDTO
+    └── ChatMessage.ts    # ChatMessage, Conversation, SendMessageDTO, CreateMessageDTO,
+                          # GetMessagesOptions, ChatResponse, ConversationSummary
+```
+
+**Key Types:**
+- `User`: id, email, displayName, passwordHash?, createdAt?, updatedAt?
+- `CalendarEvent`: id, userId, title, description?, startTime, endTime, note?, isRecurring?, recurrenceRule?
+- `ChatMessage`: id, conversationId, sender ('user' | 'assistant'), content, proposedEvent?
+- `Conversation`: id, userId, createdAt?, updatedAt? (messages loaded separately via lazy loading)
+- `CreateEventDTO`: Used for creating events AND for AI-proposed events
+- `GetMessagesOptions`: Cursor-based pagination with `before?: string` and `limit?: number`
+- `ConversationSummary`: id, lastMessage?, createdAt? (for conversation list)
+
+### Database Abstraction
+
+The repository pattern allows swapping databases:
+- **Interfaces** (`services/interfaces/`) are DB-agnostic
+- **Implementations** (`repositories/mongo/`) are DB-specific
+- To add MySQL: create `repositories/mysql/` with TypeORM entities
+
+## MVP Feature Scope
+
+### Must-Have
+- Chat interface with AI assistant (text input) for event management
+- Calendar overview
+- Manual event CRUD (without AI)
+- View completed events
+- Simple reminders
+- One note per event
+- Recurring events
+
+### Nice-to-Have
+- iCalendar import/export
+- Multiple calendars
+- CalDAV synchronization with external services
+
+## Current Implementation Status
+
+**Backend:** Skeleton complete - all files exist with `throw new Error('Not implemented')` placeholders. Ready for step-by-step implementation.
+
+**Shared:** Types and DTOs defined and exported.
+
+**Frontend:** Calendar screen partially implemented, Chat screen exists but not connected to backend.
+
+## Documentation
+
+Detailed architecture diagrams are in `docs/`:
+- `technisches_brainstorm.tex` - Technical concept document (German)
+- `architecture-class-diagram.puml` - Backend class diagram
+- `frontend-class-diagram.puml` - Frontend class diagram
+- `component-diagram.puml` - System component overview
diff --git a/apps/server/package.json b/apps/server/package.json
index 9efc39e..0cc6599 100644
--- a/apps/server/package.json
+++ b/apps/server/package.json
@@ -8,12 +8,19 @@
     "start": "node dist/app.js"
   },
   "dependencies": {
+    "@anthropic-ai/sdk": "^0.71.2",
     "@caldav/shared": "*",
-    "express": "^5.2.1"
+    "bcrypt": "^6.0.0",
+    "express": "^5.2.1",
+    "jsonwebtoken": "^9.0.3",
+    "mongoose": "^9.1.1"
   },
   "devDependencies": {
+    "@types/bcrypt": "^6.0.0",
     "@types/express": "^5.0.6",
+    "@types/jsonwebtoken": "^9.0.10",
     "@types/node": "^24.10.1",
-    "tsx": "^4.21.0"
+    "tsx": "^4.21.0",
+    "typescript": "^5.9.3"
   }
 }
diff --git a/apps/server/src/ai/ClaudeAdapter.ts b/apps/server/src/ai/ClaudeAdapter.ts
new file mode 100644
index 0000000..030a3c9
--- /dev/null
+++ b/apps/server/src/ai/ClaudeAdapter.ts
@@ -0,0 +1,18 @@
+import Anthropic from '@anthropic-ai/sdk';
+import { AIProvider, AIContext, AIResponse } from '../services/interfaces';
+
+export class ClaudeAdapter implements AIProvider {
+  private client: Anthropic;
+  private model: string;
+
+  constructor(apiKey?: string, model: string = 'claude-3-haiku-20240307') {
+    this.client = new Anthropic({
+      apiKey: apiKey || process.env.ANTHROPIC_API_KEY,
+    });
+    this.model = model;
+  }
+
+  async processMessage(message: string, context: AIContext): Promise<AIResponse> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/ai/index.ts b/apps/server/src/ai/index.ts
new file mode 100644
index 0000000..bc63f1a
--- /dev/null
+++ b/apps/server/src/ai/index.ts
@@ -0,0 +1 @@
+export * from './ClaudeAdapter';
diff --git a/apps/server/src/app.ts b/apps/server/src/app.ts
index 1ced917..f3d2823 100644
--- a/apps/server/src/app.ts
+++ b/apps/server/src/app.ts
@@ -1,12 +1,64 @@
-import express, { Request, Response } from 'express';
+import express from 'express';
+import mongoose from 'mongoose';
+
+import { createRoutes } from './routes';
+import { AuthController, ChatController, EventController } from './controllers';
+import { AuthService, ChatService, EventService } from './services';
+import { MongoUserRepository, MongoEventRepository, MongoChatRepository } from './repositories';
+import { ClaudeAdapter } from './ai';
 
 const app = express();
-const port = 3000;
+const port = process.env.PORT || 3000;
+const mongoUri = process.env.MONGODB_URI || 'mongodb://localhost:27017/caldav';
 
-app.get('/', (req: Request, res: Response) => {
-  res.send('Hello World!');
+// Middleware
+app.use(express.json());
+
+// Initialize repositories
+const userRepo = new MongoUserRepository();
+const eventRepo = new MongoEventRepository();
+const chatRepo = new MongoChatRepository();
+
+// Initialize AI provider
+const aiProvider = new ClaudeAdapter();
+
+// Initialize services
+const authService = new AuthService(userRepo);
+const chatService = new ChatService(chatRepo, eventRepo, aiProvider);
+const eventService = new EventService(eventRepo);
+
+// Initialize controllers
+const authController = new AuthController(authService);
+const chatController = new ChatController(chatService);
+const eventController = new EventController(eventService);
+
+// Setup routes
+app.use('/api', createRoutes({
+  authController,
+  chatController,
+  eventController,
+}));
+
+// Health check
+app.get('/health', (_, res) => {
+  res.json({ status: 'ok' });
 });
 
-app.listen(port, () => {
-  console.log(`Example app listening on port ${port}`);
-});
+// Start server
+async function start() {
+  try {
+    await mongoose.connect(mongoUri);
+    console.log('Connected to MongoDB');
+
+    app.listen(port, () => {
+      console.log(`Server running on port ${port}`);
+    });
+  } catch (error) {
+    console.error('Failed to start server:', error);
+    process.exit(1);
+  }
+}
+
+start();
+
+export default app;
diff --git a/apps/server/src/controllers/AuthController.ts b/apps/server/src/controllers/AuthController.ts
new file mode 100644
index 0000000..b1f6a1d
--- /dev/null
+++ b/apps/server/src/controllers/AuthController.ts
@@ -0,0 +1,22 @@
+import { Request, Response } from 'express';
+import { AuthService } from '../services';
+
+export class AuthController {
+  constructor(private authService: AuthService) {}
+
+  async login(req: Request, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async register(req: Request, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async refresh(req: Request, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async logout(req: Request, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/controllers/ChatController.ts b/apps/server/src/controllers/ChatController.ts
new file mode 100644
index 0000000..aac7d78
--- /dev/null
+++ b/apps/server/src/controllers/ChatController.ts
@@ -0,0 +1,27 @@
+import { Response } from 'express';
+import { ChatService } from '../services';
+import { AuthenticatedRequest } from '../middleware';
+
+export class ChatController {
+  constructor(private chatService: ChatService) {}
+
+  async sendMessage(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async confirmEvent(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async rejectEvent(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async getConversations(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async getConversation(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/controllers/EventController.ts b/apps/server/src/controllers/EventController.ts
new file mode 100644
index 0000000..d6ba38f
--- /dev/null
+++ b/apps/server/src/controllers/EventController.ts
@@ -0,0 +1,31 @@
+import { Response } from 'express';
+import { EventService } from '../services';
+import { AuthenticatedRequest } from '../middleware';
+
+export class EventController {
+  constructor(private eventService: EventService) {}
+
+  async create(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async getById(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async getAll(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async getByDateRange(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async update(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async delete(req: AuthenticatedRequest, res: Response): Promise<void> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/controllers/index.ts b/apps/server/src/controllers/index.ts
new file mode 100644
index 0000000..409a32e
--- /dev/null
+++ b/apps/server/src/controllers/index.ts
@@ -0,0 +1,3 @@
+export * from './AuthController';
+export * from './ChatController';
+export * from './EventController';
diff --git a/apps/server/src/middleware/AuthMiddleware.ts b/apps/server/src/middleware/AuthMiddleware.ts
new file mode 100644
index 0000000..7fda4dd
--- /dev/null
+++ b/apps/server/src/middleware/AuthMiddleware.ts
@@ -0,0 +1,10 @@
+import { Request, Response, NextFunction } from 'express';
+import { verifyToken, TokenPayload } from '../utils/jwt';
+
+export interface AuthenticatedRequest extends Request {
+  user?: TokenPayload;
+}
+
+export function authenticate(req: AuthenticatedRequest, res: Response, next: NextFunction): void {
+  throw new Error('Not implemented');
+}
diff --git a/apps/server/src/middleware/index.ts b/apps/server/src/middleware/index.ts
new file mode 100644
index 0000000..f504f2f
--- /dev/null
+++ b/apps/server/src/middleware/index.ts
@@ -0,0 +1 @@
+export * from './AuthMiddleware';
diff --git a/apps/server/src/repositories/index.ts b/apps/server/src/repositories/index.ts
new file mode 100644
index 0000000..b9fe678
--- /dev/null
+++ b/apps/server/src/repositories/index.ts
@@ -0,0 +1 @@
+export * from './mongo';
diff --git a/apps/server/src/repositories/mongo/MongoChatRepository.ts b/apps/server/src/repositories/mongo/MongoChatRepository.ts
new file mode 100644
index 0000000..250ca05
--- /dev/null
+++ b/apps/server/src/repositories/mongo/MongoChatRepository.ts
@@ -0,0 +1,23 @@
+import { ChatMessage, Conversation, CreateMessageDTO, GetMessagesOptions } from '@caldav/shared';
+import { ChatRepository } from '../../services/interfaces';
+import { ChatMessageModel, ConversationModel } from './models';
+
+export class MongoChatRepository implements ChatRepository {
+  // Conversations
+  async getConversationsByUser(userId: string): Promise<Conversation[]> {
+    throw new Error('Not implemented');
+  }
+
+  async createConversation(userId: string): Promise<Conversation> {
+    throw new Error('Not implemented');
+  }
+
+  // Messages (cursor-based pagination)
+  async getMessages(conversationId: string, options?: GetMessagesOptions): Promise<ChatMessage[]> {
+    throw new Error('Not implemented');
+  }
+
+  async createMessage(conversationId: string, message: CreateMessageDTO): Promise<ChatMessage> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/repositories/mongo/MongoEventRepository.ts b/apps/server/src/repositories/mongo/MongoEventRepository.ts
new file mode 100644
index 0000000..ff4f442
--- /dev/null
+++ b/apps/server/src/repositories/mongo/MongoEventRepository.ts
@@ -0,0 +1,29 @@
+import { CalendarEvent, CreateEventDTO, UpdateEventDTO } from '@caldav/shared';
+import { EventRepository } from '../../services/interfaces';
+import { EventModel } from './models';
+
+export class MongoEventRepository implements EventRepository {
+  async findById(id: string): Promise<CalendarEvent | null> {
+    throw new Error('Not implemented');
+  }
+
+  async findByUserId(userId: string): Promise<CalendarEvent[]> {
+    throw new Error('Not implemented');
+  }
+
+  async findByDateRange(userId: string, startDate: Date, endDate: Date): Promise<CalendarEvent[]> {
+    throw new Error('Not implemented');
+  }
+
+  async create(userId: string, data: CreateEventDTO): Promise<CalendarEvent> {
+    throw new Error('Not implemented');
+  }
+
+  async update(id: string, data: UpdateEventDTO): Promise<CalendarEvent | null> {
+    throw new Error('Not implemented');
+  }
+
+  async delete(id: string): Promise<boolean> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/repositories/mongo/MongoUserRepository.ts b/apps/server/src/repositories/mongo/MongoUserRepository.ts
new file mode 100644
index 0000000..72e64ca
--- /dev/null
+++ b/apps/server/src/repositories/mongo/MongoUserRepository.ts
@@ -0,0 +1,17 @@
+import { User } from '@caldav/shared';
+import { UserRepository, CreateUserData } from '../../services/interfaces';
+import { UserModel } from './models';
+
+export class MongoUserRepository implements UserRepository {
+  async findById(id: string): Promise<User | null> {
+    throw new Error('Not implemented');
+  }
+
+  async findByEmail(email: string): Promise<User | null> {
+    throw new Error('Not implemented');
+  }
+
+  async create(data: CreateUserData): Promise<User> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/repositories/mongo/index.ts b/apps/server/src/repositories/mongo/index.ts
new file mode 100644
index 0000000..224258a
--- /dev/null
+++ b/apps/server/src/repositories/mongo/index.ts
@@ -0,0 +1,3 @@
+export * from './MongoUserRepository';
+export * from './MongoEventRepository';
+export * from './MongoChatRepository';
diff --git a/apps/server/src/repositories/mongo/models/ChatModel.ts b/apps/server/src/repositories/mongo/models/ChatModel.ts
new file mode 100644
index 0000000..5e9841d
--- /dev/null
+++ b/apps/server/src/repositories/mongo/models/ChatModel.ts
@@ -0,0 +1,74 @@
+import mongoose, { Schema, Document } from 'mongoose';
+import { ChatMessage, Conversation, CreateEventDTO } from '@caldav/shared';
+
+export interface ChatMessageDocument extends Omit<ChatMessage, 'id'>, Document {}
+export interface ConversationDocument extends Omit<Conversation, 'id'>, Document {}
+
+const ProposedEventSchema = new Schema<CreateEventDTO>(
+  {
+    title: { type: String, required: true },
+    description: { type: String },
+    startTime: { type: Date, required: true },
+    endTime: { type: Date, required: true },
+    note: { type: String },
+    isRecurring: { type: Boolean },
+    recurrenceRule: { type: String },
+  },
+  { _id: false }
+);
+
+const ChatMessageSchema = new Schema<ChatMessageDocument>(
+  {
+    conversationId: {
+      type: String,
+      required: true,
+    },
+    sender: {
+      type: String,
+      enum: ['user', 'assistant'],
+      required: true,
+    },
+    content: {
+      type: String,
+      required: true,
+    },
+    proposedEvent: {
+      type: ProposedEventSchema,
+    },
+  },
+  {
+    timestamps: true,
+    toJSON: {
+      transform: (_, ret: Record<string, unknown>) => {
+        ret.id = String(ret._id);
+        delete ret._id;
+        delete ret.__v;
+        return ret;
+      },
+    },
+  }
+);
+
+const ConversationSchema = new Schema<ConversationDocument>(
+  {
+    userId: {
+      type: String,
+      required: true,
+      index: true,
+    },
+  },
+  {
+    timestamps: true,
+    toJSON: {
+      transform: (_, ret: Record<string, unknown>) => {
+        ret.id = String(ret._id);
+        delete ret._id;
+        delete ret.__v;
+        return ret;
+      },
+    },
+  }
+);
+
+export const ChatMessageModel = mongoose.model<ChatMessageDocument>('ChatMessage', ChatMessageSchema);
+export const ConversationModel = mongoose.model<ConversationDocument>('Conversation', ConversationSchema);
diff --git a/apps/server/src/repositories/mongo/models/EventModel.ts b/apps/server/src/repositories/mongo/models/EventModel.ts
new file mode 100644
index 0000000..6544a2e
--- /dev/null
+++ b/apps/server/src/repositories/mongo/models/EventModel.ts
@@ -0,0 +1,56 @@
+import mongoose, { Schema, Document } from 'mongoose';
+import { CalendarEvent } from '@caldav/shared';
+
+export interface EventDocument extends Omit<CalendarEvent, 'id'>, Document {}
+
+const EventSchema = new Schema<EventDocument>(
+  {
+    userId: {
+      type: String,
+      required: true,
+      index: true,
+    },
+    title: {
+      type: String,
+      required: true,
+      trim: true,
+    },
+    description: {
+      type: String,
+      trim: true,
+    },
+    startTime: {
+      type: Date,
+      required: true,
+    },
+    endTime: {
+      type: Date,
+      required: true,
+    },
+    note: {
+      type: String,
+    },
+    isRecurring: {
+      type: Boolean,
+      default: false,
+    },
+    recurrenceRule: {
+      type: String,
+    },
+  },
+  {
+    timestamps: true,
+    toJSON: {
+      transform: (_, ret: Record<string, unknown>) => {
+        ret.id = String(ret._id);
+        delete ret._id;
+        delete ret.__v;
+        return ret;
+      },
+    },
+  }
+);
+
+EventSchema.index({ userId: 1, startTime: 1, endTime: 1 });
+
+export const EventModel = mongoose.model<EventDocument>('Event', EventSchema);
diff --git a/apps/server/src/repositories/mongo/models/UserModel.ts b/apps/server/src/repositories/mongo/models/UserModel.ts
new file mode 100644
index 0000000..c256ebc
--- /dev/null
+++ b/apps/server/src/repositories/mongo/models/UserModel.ts
@@ -0,0 +1,39 @@
+import mongoose, { Schema, Document } from 'mongoose';
+import { User } from '@caldav/shared';
+
+export interface UserDocument extends Omit<User, 'id'>, Document {}
+
+const UserSchema = new Schema<UserDocument>(
+  {
+    email: {
+      type: String,
+      required: true,
+      unique: true,
+      lowercase: true,
+      trim: true,
+    },
+    displayName: {
+      type: String,
+      required: true,
+      trim: true,
+    },
+    passwordHash: {
+      type: String,
+      required: true,
+    },
+  },
+  {
+    timestamps: true,
+    toJSON: {
+      transform: (_, ret: Record<string, unknown>) => {
+        ret.id = String(ret._id);
+        delete ret._id;
+        delete ret.__v;
+        delete ret.passwordHash;
+        return ret;
+      },
+    },
+  }
+);
+
+export const UserModel = mongoose.model<UserDocument>('User', UserSchema);
diff --git a/apps/server/src/repositories/mongo/models/index.ts b/apps/server/src/repositories/mongo/models/index.ts
new file mode 100644
index 0000000..6ef5ca1
--- /dev/null
+++ b/apps/server/src/repositories/mongo/models/index.ts
@@ -0,0 +1,3 @@
+export * from './UserModel';
+export * from './EventModel';
+export * from './ChatModel';
diff --git a/apps/server/src/routes/auth.routes.ts b/apps/server/src/routes/auth.routes.ts
new file mode 100644
index 0000000..a3ac2bc
--- /dev/null
+++ b/apps/server/src/routes/auth.routes.ts
@@ -0,0 +1,13 @@
+import { Router } from 'express';
+import { AuthController } from '../controllers';
+
+export function createAuthRoutes(authController: AuthController): Router {
+  const router = Router();
+
+  router.post('/login', (req, res) => authController.login(req, res));
+  router.post('/register', (req, res) => authController.register(req, res));
+  router.post('/refresh', (req, res) => authController.refresh(req, res));
+  router.post('/logout', (req, res) => authController.logout(req, res));
+
+  return router;
+}
diff --git a/apps/server/src/routes/chat.routes.ts b/apps/server/src/routes/chat.routes.ts
new file mode 100644
index 0000000..ba48824
--- /dev/null
+++ b/apps/server/src/routes/chat.routes.ts
@@ -0,0 +1,17 @@
+import { Router } from 'express';
+import { ChatController } from '../controllers';
+import { authenticate } from '../middleware';
+
+export function createChatRoutes(chatController: ChatController): Router {
+  const router = Router();
+
+  router.use(authenticate);
+
+  router.post('/message', (req, res) => chatController.sendMessage(req, res));
+  router.post('/confirm/:conversationId/:messageId', (req, res) => chatController.confirmEvent(req, res));
+  router.post('/reject/:conversationId/:messageId', (req, res) => chatController.rejectEvent(req, res));
+  router.get('/conversations', (req, res) => chatController.getConversations(req, res));
+  router.get('/conversations/:id', (req, res) => chatController.getConversation(req, res));
+
+  return router;
+}
diff --git a/apps/server/src/routes/event.routes.ts b/apps/server/src/routes/event.routes.ts
new file mode 100644
index 0000000..a7deb5f
--- /dev/null
+++ b/apps/server/src/routes/event.routes.ts
@@ -0,0 +1,18 @@
+import { Router } from 'express';
+import { EventController } from '../controllers';
+import { authenticate } from '../middleware';
+
+export function createEventRoutes(eventController: EventController): Router {
+  const router = Router();
+
+  router.use(authenticate);
+
+  router.post('/', (req, res) => eventController.create(req, res));
+  router.get('/', (req, res) => eventController.getAll(req, res));
+  router.get('/range', (req, res) => eventController.getByDateRange(req, res));
+  router.get('/:id', (req, res) => eventController.getById(req, res));
+  router.put('/:id', (req, res) => eventController.update(req, res));
+  router.delete('/:id', (req, res) => eventController.delete(req, res));
+
+  return router;
+}
diff --git a/apps/server/src/routes/index.ts b/apps/server/src/routes/index.ts
new file mode 100644
index 0000000..86bcaac
--- /dev/null
+++ b/apps/server/src/routes/index.ts
@@ -0,0 +1,25 @@
+import { Router } from 'express';
+import { createAuthRoutes } from './auth.routes';
+import { createChatRoutes } from './chat.routes';
+import { createEventRoutes } from './event.routes';
+import { AuthController, ChatController, EventController } from '../controllers';
+
+export interface Controllers {
+  authController: AuthController;
+  chatController: ChatController;
+  eventController: EventController;
+}
+
+export function createRoutes(controllers: Controllers): Router {
+  const router = Router();
+
+  router.use('/auth', createAuthRoutes(controllers.authController));
+  router.use('/chat', createChatRoutes(controllers.chatController));
+  router.use('/events', createEventRoutes(controllers.eventController));
+
+  return router;
+}
+
+export * from './auth.routes';
+export * from './chat.routes';
+export * from './event.routes';
diff --git a/apps/server/src/services/AuthService.ts b/apps/server/src/services/AuthService.ts
new file mode 100644
index 0000000..1e3da85
--- /dev/null
+++ b/apps/server/src/services/AuthService.ts
@@ -0,0 +1,24 @@
+import { User, CreateUserDTO, LoginDTO, AuthResponse } from '@caldav/shared';
+import { UserRepository } from './interfaces';
+import * as jwt from '../utils/jwt';
+import * as password from '../utils/password';
+
+export class AuthService {
+  constructor(private userRepo: UserRepository) {}
+
+  async login(data: LoginDTO): Promise<AuthResponse> {
+    throw new Error('Not implemented');
+  }
+
+  async register(data: CreateUserDTO): Promise<AuthResponse> {
+    throw new Error('Not implemented');
+  }
+
+  async refreshToken(refreshToken: string): Promise<AuthResponse> {
+    throw new Error('Not implemented');
+  }
+
+  async logout(userId: string): Promise<void> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/services/ChatService.ts b/apps/server/src/services/ChatService.ts
new file mode 100644
index 0000000..5adc9bd
--- /dev/null
+++ b/apps/server/src/services/ChatService.ts
@@ -0,0 +1,30 @@
+import { ChatMessage, ChatResponse, SendMessageDTO, CalendarEvent, ConversationSummary, GetMessagesOptions } from '@caldav/shared';
+import { ChatRepository, EventRepository, AIProvider } from './interfaces';
+
+export class ChatService {
+  constructor(
+    private chatRepo: ChatRepository,
+    private eventRepo: EventRepository,
+    private aiProvider: AIProvider
+  ) {}
+
+  async processMessage(userId: string, data: SendMessageDTO): Promise<ChatResponse> {
+    throw new Error('Not implemented');
+  }
+
+  async confirmEvent(userId: string, conversationId: string, messageId: string): Promise<CalendarEvent> {
+    throw new Error('Not implemented');
+  }
+
+  async rejectEvent(conversationId: string, messageId: string): Promise<void> {
+    throw new Error('Not implemented');
+  }
+
+  async getConversations(userId: string): Promise<ConversationSummary[]> {
+    throw new Error('Not implemented');
+  }
+
+  async getConversation(userId: string, conversationId: string, options?: GetMessagesOptions): Promise<ChatMessage[]> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/services/EventService.ts b/apps/server/src/services/EventService.ts
new file mode 100644
index 0000000..acbace8
--- /dev/null
+++ b/apps/server/src/services/EventService.ts
@@ -0,0 +1,30 @@
+import { CalendarEvent, CreateEventDTO, UpdateEventDTO } from '@caldav/shared';
+import { EventRepository } from './interfaces';
+
+export class EventService {
+  constructor(private eventRepo: EventRepository) {}
+
+  async create(userId: string, data: CreateEventDTO): Promise<CalendarEvent> {
+    throw new Error('Not implemented');
+  }
+
+  async getById(id: string, userId: string): Promise<CalendarEvent | null> {
+    throw new Error('Not implemented');
+  }
+
+  async getAll(userId: string): Promise<CalendarEvent[]> {
+    throw new Error('Not implemented');
+  }
+
+  async getByDateRange(userId: string, startDate: Date, endDate: Date): Promise<CalendarEvent[]> {
+    throw new Error('Not implemented');
+  }
+
+  async update(id: string, userId: string, data: UpdateEventDTO): Promise<CalendarEvent | null> {
+    throw new Error('Not implemented');
+  }
+
+  async delete(id: string, userId: string): Promise<boolean> {
+    throw new Error('Not implemented');
+  }
+}
diff --git a/apps/server/src/services/index.ts b/apps/server/src/services/index.ts
new file mode 100644
index 0000000..463f4c5
--- /dev/null
+++ b/apps/server/src/services/index.ts
@@ -0,0 +1,4 @@
+export * from './AuthService';
+export * from './ChatService';
+export * from './EventService';
+export * from './interfaces';
diff --git a/apps/server/src/services/interfaces/AIProvider.ts b/apps/server/src/services/interfaces/AIProvider.ts
new file mode 100644
index 0000000..f3a8d0d
--- /dev/null
+++ b/apps/server/src/services/interfaces/AIProvider.ts
@@ -0,0 +1,16 @@
+import { CalendarEvent, ChatMessage, CreateEventDTO } from '@caldav/shared';
+
+export interface AIContext {
+  userId: string;
+  conversationHistory: ChatMessage[];
+  existingEvents: CalendarEvent[];
+}
+
+export interface AIResponse {
+  content: string;
+  proposedEvent?: CreateEventDTO;
+}
+
+export interface AIProvider {
+  processMessage(message: string, context: AIContext): Promise<AIResponse>;
+}
diff --git a/apps/server/src/services/interfaces/ChatRepository.ts b/apps/server/src/services/interfaces/ChatRepository.ts
new file mode 100644
index 0000000..ca95e5a
--- /dev/null
+++ b/apps/server/src/services/interfaces/ChatRepository.ts
@@ -0,0 +1,11 @@
+import { ChatMessage, Conversation, CreateMessageDTO, GetMessagesOptions } from '@caldav/shared';
+
+export interface ChatRepository {
+  // Conversations
+  getConversationsByUser(userId: string): Promise<Conversation[]>;
+  createConversation(userId: string): Promise<Conversation>;
+
+  // Messages (cursor-based pagination)
+  getMessages(conversationId: string, options?: GetMessagesOptions): Promise<ChatMessage[]>;
+  createMessage(conversationId: string, message: CreateMessageDTO): Promise<ChatMessage>;
+}
diff --git a/apps/server/src/services/interfaces/EventRepository.ts b/apps/server/src/services/interfaces/EventRepository.ts
new file mode 100644
index 0000000..5c4342d
--- /dev/null
+++ b/apps/server/src/services/interfaces/EventRepository.ts
@@ -0,0 +1,10 @@
+import { CalendarEvent, CreateEventDTO, UpdateEventDTO } from '@caldav/shared';
+
+export interface EventRepository {
+  findById(id: string): Promise<CalendarEvent | null>;
+  findByUserId(userId: string): Promise<CalendarEvent[]>;
+  findByDateRange(userId: string, startDate: Date, endDate: Date): Promise<CalendarEvent[]>;
+  create(userId: string, data: CreateEventDTO): Promise<CalendarEvent>;
+  update(id: string, data: UpdateEventDTO): Promise<CalendarEvent | null>;
+  delete(id: string): Promise<boolean>;
+}
diff --git a/apps/server/src/services/interfaces/UserRepository.ts b/apps/server/src/services/interfaces/UserRepository.ts
new file mode 100644
index 0000000..7103bfe
--- /dev/null
+++ b/apps/server/src/services/interfaces/UserRepository.ts
@@ -0,0 +1,13 @@
+import { User } from '@caldav/shared';
+
+export interface CreateUserData {
+  email: string;
+  displayName: string;
+  passwordHash: string;
+}
+
+export interface UserRepository {
+  findById(id: string): Promise<User | null>;
+  findByEmail(email: string): Promise<User | null>;
+  create(data: CreateUserData): Promise<User>;
+}
diff --git a/apps/server/src/services/interfaces/index.ts b/apps/server/src/services/interfaces/index.ts
new file mode 100644
index 0000000..d568496
--- /dev/null
+++ b/apps/server/src/services/interfaces/index.ts
@@ -0,0 +1,4 @@
+export * from './AIProvider';
+export * from './UserRepository';
+export * from './EventRepository';
+export * from './ChatRepository';
diff --git a/apps/server/src/utils/index.ts b/apps/server/src/utils/index.ts
new file mode 100644
index 0000000..41ed166
--- /dev/null
+++ b/apps/server/src/utils/index.ts
@@ -0,0 +1,2 @@
+export * from './jwt';
+export * from './password';
diff --git a/apps/server/src/utils/jwt.ts b/apps/server/src/utils/jwt.ts
new file mode 100644
index 0000000..c1e571f
--- /dev/null
+++ b/apps/server/src/utils/jwt.ts
@@ -0,0 +1,26 @@
+import jwt from 'jsonwebtoken';
+
+export interface TokenPayload {
+  userId: string;
+  email: string;
+}
+
+export interface JWTConfig {
+  secret: string;
+  expiresIn: string;
+}
+
+const JWT_SECRET = process.env.JWT_SECRET || 'your-secret-key';
+const JWT_EXPIRES_IN = process.env.JWT_EXPIRES_IN || '1h';
+
+export function signToken(payload: TokenPayload): string {
+  throw new Error('Not implemented');
+}
+
+export function verifyToken(token: string): TokenPayload {
+  throw new Error('Not implemented');
+}
+
+export function decodeToken(token: string): TokenPayload | null {
+  throw new Error('Not implemented');
+}
diff --git a/apps/server/src/utils/password.ts b/apps/server/src/utils/password.ts
new file mode 100644
index 0000000..825c3d3
--- /dev/null
+++ b/apps/server/src/utils/password.ts
@@ -0,0 +1,11 @@
+import bcrypt from 'bcrypt';
+
+const SALT_ROUNDS = 10;
+
+export async function hash(password: string): Promise<string> {
+  throw new Error('Not implemented');
+}
+
+export async function compare(password: string, hash: string): Promise<boolean> {
+  throw new Error('Not implemented');
+}
diff --git a/docs/Backend Klassendiagramm.png b/docs/Backend Klassendiagramm.png
new file mode 100644
index 0000000..2fa437d
Binary files /dev/null and b/docs/Backend Klassendiagramm.png differ
diff --git a/docs/Frontend Klassendiagramm.png b/docs/Frontend Klassendiagramm.png
new file mode 100644
index 0000000..4259039
Binary files /dev/null and b/docs/Frontend Klassendiagramm.png differ
diff --git a/docs/System Komponenten.png b/docs/System Komponenten.png
new file mode 100644
index 0000000..068df39
Binary files /dev/null and b/docs/System Komponenten.png differ
diff --git a/docs/architecture-class-diagram.puml b/docs/architecture-class-diagram.puml
index 19fa1b9..27aadcb 100644
--- a/docs/architecture-class-diagram.puml
+++ b/docs/architecture-class-diagram.puml
@@ -38,7 +38,7 @@ package "Controller Layer" #ADD8E6 {
 }
 
 package "Service Layer" #90EE90 {
-    package "Interfaces" {
+    package "Data Access Interfaces" {
         interface AIProvider {
             ' +processMessage()
         }
@@ -94,7 +94,7 @@ package "AI Layer" #FFA07A {
     }
 }
 
-package "Data Access Layer" #FFD700 {
+package "Data Access Implementations" #FFD700 {
     class MongoUserRepository implements UserRepository {
         ' -model: UserModel
     }
diff --git a/package-lock.json b/package-lock.json
index b51015d..cdfa599 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -60,13 +60,20 @@
       "name": "@caldav/server",
       "version": "1.0.0",
       "dependencies": {
+        "@anthropic-ai/sdk": "^0.71.2",
         "@caldav/shared": "*",
-        "express": "^5.2.1"
+        "bcrypt": "^6.0.0",
+        "express": "^5.2.1",
+        "jsonwebtoken": "^9.0.3",
+        "mongoose": "^9.1.1"
       },
       "devDependencies": {
+        "@types/bcrypt": "^6.0.0",
         "@types/express": "^5.0.6",
+        "@types/jsonwebtoken": "^9.0.10",
         "@types/node": "^24.10.1",
-        "tsx": "^4.21.0"
+        "tsx": "^4.21.0",
+        "typescript": "^5.9.3"
       }
     },
     "node_modules/@0no-co/graphql.web": {
@@ -95,6 +102,26 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/@anthropic-ai/sdk": {
+      "version": "0.71.2",
+      "resolved": "https://registry.npmjs.org/@anthropic-ai/sdk/-/sdk-0.71.2.tgz",
+      "integrity": "sha512-TGNDEUuEstk/DKu0/TflXAEt+p+p/WhTlFzEnoosvbaDU2LTjm42igSdlL0VijrKpWejtOKxX0b8A7uc+XiSAQ==",
+      "license": "MIT",
+      "dependencies": {
+        "json-schema-to-ts": "^3.1.1"
+      },
+      "bin": {
+        "anthropic-ai-sdk": "bin/cli"
+      },
+      "peerDependencies": {
+        "zod": "^3.25.0 || ^4.0.0"
+      },
+      "peerDependenciesMeta": {
+        "zod": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/@babel/code-frame": {
       "version": "7.27.1",
       "resolved": "https://registry.npmjs.org/@babel/code-frame/-/code-frame-7.27.1.tgz",
@@ -3239,6 +3266,15 @@
         "@jridgewell/sourcemap-codec": "^1.4.14"
       }
     },
+    "node_modules/@mongodb-js/saslprep": {
+      "version": "1.4.4",
+      "resolved": "https://registry.npmjs.org/@mongodb-js/saslprep/-/saslprep-1.4.4.tgz",
+      "integrity": "sha512-p7X/ytJDIdwUfFL/CLOhKgdfJe1Fa8uw9seJYvdOmnP9JBWGWHW69HkOixXS6Wy9yvGf1MbhcS6lVmrhy4jm2g==",
+      "license": "MIT",
+      "dependencies": {
+        "sparse-bitfield": "^3.0.3"
+      }
+    },
     "node_modules/@napi-rs/wasm-runtime": {
       "version": "0.2.12",
       "resolved": "https://registry.npmjs.org/@napi-rs/wasm-runtime/-/wasm-runtime-0.2.12.tgz",
@@ -3935,6 +3971,16 @@
         "@babel/types": "^7.28.2"
       }
     },
+    "node_modules/@types/bcrypt": {
+      "version": "6.0.0",
+      "resolved": "https://registry.npmjs.org/@types/bcrypt/-/bcrypt-6.0.0.tgz",
+      "integrity": "sha512-/oJGukuH3D2+D+3H4JWLaAsJ/ji86dhRidzZ/Od7H/i8g+aCmvkeCc6Ni/f9uxGLSQVCRZkX2/lqEFG2BvWtlQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/body-parser": {
       "version": "1.19.6",
       "resolved": "https://registry.npmjs.org/@types/body-parser/-/body-parser-1.19.6.tgz",
@@ -4048,6 +4094,24 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/jsonwebtoken": {
+      "version": "9.0.10",
+      "resolved": "https://registry.npmjs.org/@types/jsonwebtoken/-/jsonwebtoken-9.0.10.tgz",
+      "integrity": "sha512-asx5hIG9Qmf/1oStypjanR7iKTv0gXQ1Ov/jfrX6kS/EO0OFni8orbmGCn0672NHR3kXHwpAwR+B368ZGN/2rA==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/ms": "*",
+        "@types/node": "*"
+      }
+    },
+    "node_modules/@types/ms": {
+      "version": "2.1.0",
+      "resolved": "https://registry.npmjs.org/@types/ms/-/ms-2.1.0.tgz",
+      "integrity": "sha512-GsCCIZDE/p3i96vtEqx+7dBUGXrc7zeSK3wwPHIaRThS+9OhWIXRqzs4d6k1SVU8g91DrNRWxWUGhp5KXQb2VA==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@types/node": {
       "version": "24.10.1",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-24.10.1.tgz",
@@ -4108,6 +4172,21 @@
       "integrity": "sha512-9aEbYZ3TbYMznPdcdr3SmIrLXwC/AKZXQeCf9Pgao5CKb8CyHuEX5jzWPTkvregvhRJHcpRO6BFoGW9ycaOkYw==",
       "license": "MIT"
     },
+    "node_modules/@types/webidl-conversions": {
+      "version": "7.0.3",
+      "resolved": "https://registry.npmjs.org/@types/webidl-conversions/-/webidl-conversions-7.0.3.tgz",
+      "integrity": "sha512-CiJJvcRtIgzadHCYXw7dqEnMNRjhGZlYK05Mj9OyktqV8uVT8fD2BFOB7S1uwBE3Kj2Z+4UyPmFw/Ixgw/LAlA==",
+      "license": "MIT"
+    },
+    "node_modules/@types/whatwg-url": {
+      "version": "13.0.0",
+      "resolved": "https://registry.npmjs.org/@types/whatwg-url/-/whatwg-url-13.0.0.tgz",
+      "integrity": "sha512-N8WXpbE6Wgri7KUSvrmQcqrMllKZ9uxkYWMt+mCSGwNc0Hsw9VQTW7ApqI4XNrx6/SaM2QQJCzMPDEXE058s+Q==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/webidl-conversions": "*"
+      }
+    },
     "node_modules/@types/yargs": {
       "version": "17.0.35",
       "resolved": "https://registry.npmjs.org/@types/yargs/-/yargs-17.0.35.tgz",
@@ -5342,6 +5421,20 @@
         "baseline-browser-mapping": "dist/cli.js"
       }
     },
+    "node_modules/bcrypt": {
+      "version": "6.0.0",
+      "resolved": "https://registry.npmjs.org/bcrypt/-/bcrypt-6.0.0.tgz",
+      "integrity": "sha512-cU8v/EGSrnH+HnxV2z0J7/blxH8gq7Xh2JFT6Aroax7UohdmiJJlxApMxtKfuI7z68NvvVcmR78k2LbT6efhRg==",
+      "hasInstallScript": true,
+      "license": "MIT",
+      "dependencies": {
+        "node-addon-api": "^8.3.0",
+        "node-gyp-build": "^4.8.4"
+      },
+      "engines": {
+        "node": ">= 18"
+      }
+    },
     "node_modules/better-opn": {
       "version": "3.0.2",
       "resolved": "https://registry.npmjs.org/better-opn/-/better-opn-3.0.2.tgz",
@@ -5513,6 +5606,15 @@
         "node-int64": "^0.4.0"
       }
     },
+    "node_modules/bson": {
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@@ -9491,6 +9655,36 @@
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@@ -9862,6 +10092,12 @@
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@@ -10494,6 +10736,138 @@
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+        "mongodb": "~7.0",
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+        "sift": "17.1.3"
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+      "engines": {
+        "node": ">=20.19.0"
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+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/mongoose"
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+    },
+    "node_modules/mpath": {
+      "version": "0.9.0",
+      "resolved": "https://registry.npmjs.org/mpath/-/mpath-0.9.0.tgz",
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+      "license": "MIT",
+      "engines": {
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+      "license": "MIT",
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       "license": "MIT"
     },
+    "node_modules/node-addon-api": {
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+      "resolved": "https://registry.npmjs.org/node-addon-api/-/node-addon-api-8.5.0.tgz",
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+      "license": "MIT",
+      "engines": {
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+      }
+    },
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       "version": "2.7.0",
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@@ -10613,6 +10996,17 @@
         "node": ">= 6.13.0"
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+      "version": "4.8.4",
+      "resolved": "https://registry.npmjs.org/node-gyp-build/-/node-gyp-build-4.8.4.tgz",
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+      "license": "MIT",
+      "bin": {
+        "node-gyp-build": "bin.js",
+        "node-gyp-build-optional": "optional.js",
+        "node-gyp-build-test": "build-test.js"
+      }
+    },
     "node_modules/node-int64": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/node-int64/-/node-int64-0.4.0.tgz",
@@ -13224,6 +13618,12 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/sift": {
+      "version": "17.1.3",
+      "resolved": "https://registry.npmjs.org/sift/-/sift-17.1.3.tgz",
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+      "license": "MIT"
+    },
     "node_modules/signal-exit": {
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       "resolved": "https://registry.npmjs.org/signal-exit/-/signal-exit-3.0.7.tgz",
@@ -13323,6 +13723,15 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/sparse-bitfield": {
+      "version": "3.0.3",
+      "resolved": "https://registry.npmjs.org/sparse-bitfield/-/sparse-bitfield-3.0.3.tgz",
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+      "license": "MIT",
+      "dependencies": {
+        "memory-pager": "^1.0.2"
+      }
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     "node_modules/split-on-first": {
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       "resolved": "https://registry.npmjs.org/split-on-first/-/split-on-first-1.1.0.tgz",
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       "license": "MIT"
     },
+    "node_modules/ts-algebra": {
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+      "resolved": "https://registry.npmjs.org/ts-algebra/-/ts-algebra-2.0.0.tgz",
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diff --git a/packages/shared/package.json b/packages/shared/package.json
index ddb0b4b..1ac2404 100644
--- a/packages/shared/package.json
+++ b/packages/shared/package.json
@@ -2,7 +2,10 @@
   "name": "@caldav/shared",
   "version": "1.0.0",
   "private": true,
+  "main": "./src/index.ts",
+  "types": "./src/index.ts",
   "exports": {
+    ".": "./src/index.ts",
     "./*": "./src/*"
   }
 }
diff --git a/packages/shared/src/index.ts b/packages/shared/src/index.ts
new file mode 100644
index 0000000..e9644da
--- /dev/null
+++ b/packages/shared/src/index.ts
@@ -0,0 +1 @@
+export * from './models';
diff --git a/packages/shared/src/models/CalendarEvent.ts b/packages/shared/src/models/CalendarEvent.ts
new file mode 100644
index 0000000..4e59e3d
--- /dev/null
+++ b/packages/shared/src/models/CalendarEvent.ts
@@ -0,0 +1,33 @@
+export interface CalendarEvent {
+  id: string;
+  userId: string;
+  title: string;
+  description?: string;
+  startTime: Date;
+  endTime: Date;
+  note?: string;
+  isRecurring?: boolean;
+  recurrenceRule?: string;
+  createdAt?: Date;
+  updatedAt?: Date;
+}
+
+export interface CreateEventDTO {
+  title: string;
+  description?: string;
+  startTime: Date;
+  endTime: Date;
+  note?: string;
+  isRecurring?: boolean;
+  recurrenceRule?: string;
+}
+
+export interface UpdateEventDTO {
+  title?: string;
+  description?: string;
+  startTime?: Date;
+  endTime?: Date;
+  note?: string;
+  isRecurring?: boolean;
+  recurrenceRule?: string;
+}
diff --git a/packages/shared/src/models/ChatMessage.ts b/packages/shared/src/models/ChatMessage.ts
new file mode 100644
index 0000000..2ddec96
--- /dev/null
+++ b/packages/shared/src/models/ChatMessage.ts
@@ -0,0 +1,46 @@
+import { CreateEventDTO } from './CalendarEvent';
+
+export type MessageSender = 'user' | 'assistant';
+
+export interface ChatMessage {
+  id: string;
+  conversationId: string;
+  sender: MessageSender;
+  content: string;
+  proposedEvent?: CreateEventDTO;
+  createdAt?: Date;
+}
+
+export interface Conversation {
+  id: string;
+  userId: string;
+  createdAt?: Date;
+  updatedAt?: Date;
+}
+
+export interface SendMessageDTO {
+  conversationId?: string;
+  content: string;
+}
+
+export interface CreateMessageDTO {
+  sender: MessageSender;
+  content: string;
+  proposedEvent?: CreateEventDTO;
+}
+
+export interface GetMessagesOptions {
+  before?: string;  // Message ID - load messages before this one
+  limit?: number;   // Default: 20
+}
+
+export interface ChatResponse {
+  message: ChatMessage;
+  conversationId: string;
+}
+
+export interface ConversationSummary {
+  id: string;
+  lastMessage?: ChatMessage;
+  createdAt?: Date;
+}
diff --git a/packages/shared/src/models/User.ts b/packages/shared/src/models/User.ts
new file mode 100644
index 0000000..30485c0
--- /dev/null
+++ b/packages/shared/src/models/User.ts
@@ -0,0 +1,25 @@
+export interface User {
+  id: string;
+  email: string;
+  displayName: string;
+  passwordHash?: string;
+  createdAt?: Date;
+  updatedAt?: Date;
+}
+
+export interface CreateUserDTO {
+  email: string;
+  displayName: string;
+  password: string;
+}
+
+export interface LoginDTO {
+  email: string;
+  password: string;
+}
+
+export interface AuthResponse {
+  user: Omit<User, 'passwordHash'>;
+  accessToken: string;
+  refreshToken?: string;
+}
diff --git a/packages/shared/src/models/index.ts b/packages/shared/src/models/index.ts
new file mode 100644
index 0000000..f00dc4c
--- /dev/null
+++ b/packages/shared/src/models/index.ts
@@ -0,0 +1,3 @@
+export * from './User';
+export * from './CalendarEvent';
+export * from './ChatMessage';