WebSocket
A protocol for full-duplex communication over a single TCP connection. Unlike HTTP, the server can push data to the client without being asked.
What is WebSocket?
A protocol for full-duplex communication over a single TCP connection. Unlike HTTP, the server can push data to the client without being asked.
WebSocket is a intermediate-level concept that sits in the API Design & Protocols area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "WebSocket" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn WebSocket in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the WebSocket lessonRelated lessons
Lessons that touch on WebSocket as part of a larger topic.
WebSockets
Full-duplex, persistent connections, how the real-time web actually works
intermediate · messaging event systems
Design a Chat System like WhatsApp
Design a real-time messaging system - WebSockets, message ordering, end-to-end encryption, presence, and group chats at billion-user scale
capstone · capstone
Design a Real-Time Analytics Dashboard
Design a real-time analytics system - stream processing, WebSocket-powered dashboards, aggregation pipelines, and windowed computations at scale
capstone · capstone
Server-Sent Events (SSE)
One-way server push over HTTP, real-time updates without the complexity of WebSockets
intermediate · messaging event systems
See also
Related glossary terms you might want to look up next.
SSE
Server-Sent Events: a one-way channel where the server pushes updates to the client over HTTP. Simpler than WebSockets when you only need server-to-client streaming.
HTTP
The protocol powering the web. A request-response model where clients ask for resources and servers respond. Stateless by design.
TCP
A reliable transport protocol that guarantees data arrives in order and without errors. It uses a three-way handshake to establish connections.