The HTTP 418 I'm a teapot client error response code indicates that the server refuses to brew coffee because it is, permanently, a teapot. A combined coffee/tea pot that is temporarily out of coffee should instead return 503. This error is a reference to Hyper Text Coffee Pot Control Protocol defined in April Fools’ jokes in 1998 and 2014.

Some websites use this response for requests they do not wish to handle, such as automated queries.

418 I'm a teapot

Hyper Text Coffee Pot Control Protocol

The Hyper Text Coffee Pot Control Protocol (HTCPCP) is a facetious communication protocol for controlling, monitoring, and diagnosing coffee pots. It is specified in RFC 2324, published on 1 April 1998 as an April Fools’ Day RFC, as part of an April Fools prank

An extension, HTCPCP-TEA, was published as RFC 7168 on 1 April 2014 to support brewing teas, which is also an April Fools’ Day RFC

Protocol

RFC 2324 was written by Larry Masinter, who describes it as a satire, saying “This has a serious purpose – it identifies many of the ways in which HTTP has been extended inappropriately.” The wording of the protocol made it clear that it was not entirely serious; for example, it notes that “there is a strong, dark, rich requirement for a protocol designed espressoly [sic] for the brewing of coffee”.

Despite the joking nature of its origins, or perhaps because of it, the protocol has remained as a minor presence online. The editor Emacs includes a fully functional client side implementation of it, and a number of bug reports exist complaining about Mozilla’s lack of support for the protocol.

Ten years after the publication of HTCPCP, the Web-Controlled Coffee Consortium (WC3) published a first draft of “HTCPCP Vocabulary in RDF” in parody of the World Wide Web Consortium’s (W3C) “HTTP Vocabulary in RDF”.

On April 1, 2014, RFC 7168 extended HTCPCP to fully handle teapots.