Server-Sent Events (SSE) is a server push technology enabling a client to receive automatic updates from a server via an HTTP connection, and describes how servers can initiate data transmission towards clients once an initial client connection has been established. They are commonly used to send message updates or continuous data streams to a browser client and designed to enhance native, cross-browser streaming through a JavaScript API called EventSource, through which a client requests a particular URL in order to receive an event stream. The EventSource API is standardized as part of

HTML5 HTML5 is a markup language used for structuring and presenting content on the World Wide Web. It is the fifth and final major HTML version that is a World Wide Web Consortium (W3C) recommendation. The current specification is known as the HT ...

by the

WHATWG The Web Hypertext Application Technology Working Group (WHATWG) is a community of people interested in evolving HTML and related technologies. The WHATWG was founded by individuals from Apple Inc., the Mozilla Foundation and Opera Software, ...

. The

mime type A media type (also known as a MIME type) is a two-part identifier for file formats and format contents transmitted on the Internet. The Internet Assigned Numbers Authority (IANA) is the official authority for the standardization and publication o ...

for SSE is text/event-stream.

History

The SSE mechanism was first specified by

Ian Hickson Ian "Hixie" Hickson is the author and maintainer of the Acid2 and Acid3 tests, the WHATWG HTML 5 specification,

as part of the "

Web Applications 1.0" proposal starting in 2004. In September 2006, the

Opera web browser Opera is a multi-platform web browser developed by its namesake company Opera. The browser is based on Chromium, but distinguishes itself from other Chromium-based browsers (Chrome, Edge, etc.) through its user interface and other features. ...

implemented the experimental technology in a feature called "Server-Sent Events".Stream Updates with Server-Sent Events, Eric Bidelman, HTML5Rocks website.<