Real-Time Web Applications: WebSockets vs Server-Sent Events (SSE) Deep Dive

1. The Demise of Polling

Gone are the days when web clients had to send an HTTP request every 3 seconds to check for new messages or order updates. Short polling wastes massive server CPU cycles, floods access logs, and burns mobile battery life.

Modern real-time systems require **persistent connections**. The two dominant standards are **Server-Sent Events (SSE)** and **WebSockets**.

2. Server-Sent Events (SSE): The AI Streaming Hero

Server-Sent Events allow a server to stream text data unidirectionally to the browser over standard HTTP/2 or HTTP/3 connections.

Why SSE has exploded with Generative AI: - **Zero Special Protocol Handshakes:** Runs over ordinary HTTPS (port 443), passing effortlessly through corporate firewalls and proxies. - **Built-in Auto-Reconnection:** Browser native `EventSource` automatically reconnects if the mobile signal drops, resuming with `Last-Event-ID`. - **Ideal For:** LLM token streaming (ChatGPT-style interfaces), live sports score tickers, and financial stock tickers.

3. WebSockets: True Full-Duplex Power

When your application requires intense, bidirectional, low-latency communication—where both client and server transmit messages simultaneously—WebSockets are king.

Key advantages: - Upgrades standard HTTP connections to a permanent TCP socket. - Minimal frame overhead (only 2 to 6 bytes per packet compared to hundreds of bytes in HTTP headers). - **Ideal For:** Multiplayer gaming, collaborative whiteboard canvases (like Figma), live chat rooms, and real-time multiplayer order dispatching.