TL;DR
Server-Sent Events (SSE) is a one-way streaming protocol from server → browser built on plain HTTP. The browser opens a connection with new EventSource(url), and the server keeps it open and pushes data: lines whenever it wants. That's it. No WebSocket handshake, no ws://, no upgrade. It auto-reconnects, it works through every proxy that speaks HTTP, and it's been in every browser since 2012.
If you need server → client streaming and you don't need bidirectional messaging, SSE beats WebSockets in almost every way that matters in 2026: less code, simpler infra, auto-reconnect, automatic event IDs for resumability. The only reasons to reach for WebSockets are bidirectional chat-style traffic or binary frames.
Want to see one streaming right now? Open the free SSE tester, paste any SSE endpoint, watch events arrive live.
The 30-Second Mental Model
