Chatly -> Real-Time Group Chat

A real-time group chat app built with FastAPI WebSockets and vanilla JS.

Live Demo

https://chat-app-2-th9p.onrender.com/

---

Features

• Real-time messaging via WebSocket
• 3 chat rooms: general, tech, random
• Message history (last 50 messages on join)
• Live online users list with presence
• Auto-reconnect with exponential backoff
• Username uniqueness per room
• No sign-up needed just pick a name and join
• XSS-safe all user content via textContent

Tech Stack

Layer	Choice	Reason
Backend	FastAPI + WebSockets	Async, Python-native WebSocket support
Database	SQLite	Zero setup, message history persistence
Frontend	Vanilla HTML/JS	No build step, fast iteration
State	In-memory ConnectionManager	Sufficient for single-instance demo

Setup

cd chat-app
python -m venv venv
venv\Scripts\activate      # Windows
pip install -r backend/requirements.txt
cd backend
uvicorn main:app --reload --port 8000

Visit http://localhost:8000

Project Structure

chat-app/
├── backend/
│   ├── main.py          # FastAPI app, WebSocket handler, ConnectionManager
│   └── requirements.txt
├── frontend/
│   ├── index.html       # Join page
│   └── chat.html        # Chat UI
├── SPEC.md              # Feature spec (written before building)
└── README.md

Deployment

Render

1. New Web Service → connect repo
2. Root Directory: backend
3. Build: pip install -r requirements.txt
4. Start: uvicorn main:app --host 0.0.0.0 --port $PORT