Backend question · HTTP & API design › WebSockets, SSE & polling

What `Content-Type` must a Server-Sent Events endpoint respond with?

text/event-stream

EventSource expects text/event-stream. This is a text format. Each message has lines like data: ... and ends with a blank line. If the server sends JSON with application/json, EventSource fails the connection.

Using server-sent events (MDN) (https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events)developer.mozilla.org