Server-Sent Events vs WebSockets

SSE and WebSockets are the two main browser-native options for real-time server-to-client communication. SSE is simpler and unidirectional. WebSockets are more powerful and bidirectional.

Server-Sent Events

SSE uses a standard HTTP connection that stays open. The server sends events in a simple text format (data:, event:, id: fields). The browser's EventSource API handles connection management, automatic reconnection, and event dispatch.

SSE's biggest advantages are simplicity and HTTP compatibility. It works through every proxy, firewall, and CDN without special configuration. The built-in reconnection with last-event-id means the client automatically resumes from where it left off after a disconnect.

WebSockets

WebSockets provide a full-duplex communication channel. After an HTTP upgrade handshake, both client and server can send messages at any time with minimal frame overhead. This enables real-time bidirectional patterns like chat and collaborative editing.

The Decision Framework

Ask: does the client need to send real-time messages to the server? If yes, use WebSockets. If the server just needs to push updates to the client, SSE is simpler, more HTTP-compatible, and has better built-in reconnection.

Many real-time features (notifications, live dashboards, progress bars) are purely server-to-client and are better served by SSE than WebSockets. See our real-time communication concepts for more patterns.

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The Bottom Line

Use SSE for server-push scenarios — it is simpler, more HTTP-friendly, and has better reconnection. Use WebSockets when you need bidirectional communication or binary data support.