Real-time basics: WebSocket versus SSE

The direction of the data flow should drive the technology choice.

• SSE is often enough for one-way streams from server to client, such as notifications or live metrics.
• WebSocket fits better when both client and server need to send messages interactively, such as in chat or collaborative tools.
• SSE has simpler connection semantics in many use cases.
• WebSocket usually requires a more explicit reconnection strategy on the client.

Without visible connection state, the interface can lie to the user.

Many real-time bugs are not socket bugs. They are state and protocol bugs.

• Ignoring heartbeat or idle timeout behavior.
• Sending messages with no clear event type or versioning contract.
• Retrying forever with no backoff.
• Treating every reconnect as if it were a clean fresh session.