Server-Sent Events

Server-Sent Events (SSE) provide a unidirectional, persistent HTTP connection for a server to push real-time, text-based data streams to a client using the standard `EventSource` API.

SSE establishes a single, long-lived HTTP connection, allowing the server to push text-based data streams to the client: it's strictly one-way communication, unlike WebSockets. The server initiates the stream by responding with the `Content-Type: text/event-stream` header and sending data blocks separated by double newlines (`\n\n`). On the client, the browser's native `EventSource` interface handles the connection, automatically managing retries and providing event IDs for resilience. This makes SSE ideal for scenarios requiring constant server-to-client updates, such as live stock tickers, sports scores, or streaming progress bar status updates, without the overhead of a full bidirectional protocol.

https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events