What is SSE?
Answer out loud or in your head first, then compare.
Answer
SSE, or Server-Sent Events, is a way of sending successive events from the server to the client over an HTTP response. The connection can stay open while the server appends further events. The main direction of this communication is server → client.
Examples are a task's progress bar or successive fragments of an AI answer. Requests the other way, e.g. “cancel the task”, can be sent separately via the API. Browsers have EventSource, but you can also read the stream with fetch. Reconnecting won't magically restore history: the server has to store events and decide how to resend them, if needed.
Why it matters: A practical solution for progress and model answers.
Possible follow-ups: What do you do if a proxy along the way buffers the whole response?
How did it go? Be honest — “Not yet” puts the question on your review list.
Practise in code
- Reading SSE events — runs tests in your browser
Further reading
- MDN: Using server-sent events(opens in a new tab)Accessed 22.10.2026. Direction of transmission and the SSE event format.