## TL;DR

WebSocket is a communication protocol providing full-duplex, bidirectional communication over a single TCP connection, standardized as IETF RFC 6455 in 2011. Unlike HTTP's request-response model, WebSocket maintains a persistent connection where both client and server can send data at any time. It is the foundation of real-time web applications including chat systems, live dashboards, collaborative editing, multiplayer games, and financial trading platforms. The protocol has universal browser support and is maintained as a living standard by WHATWG (updated March 2026).

## Core Explanation

WebSocket upgrades an HTTP connection to a persistent socket:

1. **Handshake** (HTTP Upgrade): Client sends `Upgrade: websocket` header; server responds with `101 Switching Protocols`
2. **Data Transfer**: Binary or text frames flow bidirectionally with minimal overhead (2-6 bytes per frame header vs. HTTP's ~800 bytes)
3. **Close**: Either side initiates graceful closure

Key properties:
- **Full-duplex**: Both sides can send independently
- **Low latency**: No HTTP handshake per message — 2-6 byte frame overhead
- **Binary + Text**: Native support for both message types
- **Persistent**: Connection stays open until explicitly closed

## Comparison

| Protocol | Direction | Overhead/Message | Use Case |
|----------|:---------:|:----------------:|----------|
| HTTP | Client → Server (request-driven) | ~800 bytes | Documents, APIs |
| WebSocket | Bidirectional | ~2-6 bytes | Real-time apps |
| SSE (Server-Sent Events) | Server → Client only | Low | Unidirectional push |
| WebRTC | Peer-to-peer | Variable | Video/audio, P2P data |

## Further Reading

- [RFC 6455](https://www.rfc-editor.org/rfc/rfc6455): Official IETF standard
- [WHATWG WebSocket Standard](https://websockets.spec.whatwg.org/): Living standard (2026-03-15)