WebSocket vs. Server-Sent Events: Key Differences

WebSocket and Server-Sent Events (SSE) are two technologies designed to facilitate real-time data transmission from servers to browsers, each with distinct operational characteristics and use cases. WebSocket creates a persistent, full-duplex TCP channel by upgrading a standard HTTP connection, enabling bidirectional communication where both the client and server can send messages independently. This makes it ideal for applications requiring high-frequency data exchange, like chat systems or multiplayer games. SSE, on the other hand, maintains a unidirectional flow within the HTTP framework, pushing updates from the server to the client through a never-closing HTTP response, which is simpler to implement for server-push scenarios. SSE benefits from HTTP/2 multiplexing, which removes previous browser-origin connection limitations and supports automatic reconnection and message replay, making it favorable for applications such as dashboards or live feeds where data flows primarily from server to client. Despite WebSocket's dominance due to its low-latency connections and native binary data support, the growing adoption of SSE in AI and framework integrations has shifted the conventional wisdom to favor SSE for scenarios not requiring bidirectional communication. The landscape is evolving with emerging technologies like WebTransport, which promises to bridge gaps by offering multiplexed streams over HTTP/3, though widespread browser support is still developing.