About

Error 418 – I'm a Teapot is a unique online error message that could be displayed as part of an April's Fool joke concerning a protocol code about coffee pots. The resulting error is nothing more than a subtle reference to the children's song I'm a little Teapot and is reminiscent of the Trojan Room Coffee Pot phenomenon.

Origins : the Hyper Text Coffee Pot Control Protocol

The Hyper Text Coffee Pot Control Protocol (HTCPCP for short) is a protocol for controlling, monitoring, and diagnosing coffee pots that was submitted on April 1st 1998 on RFC 2324^[1]. To sum up, RFC (Request for Comments) is a memorandum published by the Internet Engineering Task Force (IETF) describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems.
The HTCPCP was written by L. Masinter who gave an introduction of a valuable "reason" on why it should exist as a protocol, with a reference to the Internet-connected Coke Machine:

There is coffee all over the world. Increasingly, in a world in which
computing is ubiquitous, the computists want to make coffee. Coffee
brewing is an art, but the distributed intelligence of the web-
connected world transcends art. Thus, there is a strong, dark, rich
requirement for a protocol designed espressoly for the brewing of
coffee. Coffee is brewed using coffee pots. Networked coffee pots
require a control protocol if they are to be controlled.

Increasingly, home and consumer devices are being connected to the
Internet. Early networking experiments demonstrated vending devices
connected to the Internet for status monitoring [COKE]. One of the
first remotely operated machine to be hooked up to the Internet,
the Internet Toaster, (controlled via SNMP) was debuted in 1990
[RFC2235].

The demand for ubiquitous appliance connectivity that is causing the
consumption of the IPv4 address space. Consumers want remote control
of devices such as coffee pots so that they may wake up to freshly
brewed coffee, or cause coffee to be prepared at a precise time after
the completion of dinner preparations.

That memo contains a detailed list of protocols, commands, codes and replies, as defined in the wikipedia article for HTCPCP^[2].

HTCPCP requests are identified with the URI scheme coffee: (or the corresponding word in any other of the 29 listed languages) and contain several additions to the HTTP methods:
BREW or POST Causes the HTCPCP server to brew coffee
GET Retrieves coffee from the HTCPCP server
PROPFIND Finds out metadata about the coffee
WHEN Says "when", causing the HTCPCP server to stop pouring milk into the coffee (if applicable)

It also defines two error responses:
406 Not Acceptable The HTCPCP server is unable to brew coffee for some reason; the response should indicate a list of acceptable coffee types.
418 I'm a teapot The HTCPCP server is a teapot; the resulting entity may be short and stout. Demonstrations of this behaviour exist.

Popularity as an error message

in 2000, a bug report was filled to Mozilla in complaint of a lack of support for the HTCPCP and its coffee protocol^[3]. Throughout the 2000s, several websites would enable that fake error message, including personal websites like kurgan.org^[4] and the Royal Holloway University of London personal space^[5] but also other more official news sites such as the New York Times^[6] and the BBC^[7]. Many tech savvy websites like aroundtheinterwebs^[8], the Minery blog^[9] or 100pulse^[10] accounted for the error and a blog with the meme name was launched in January 2011^[11].

External References

^[1] Request For Comments 2324 – Hyper Text Coffee Pot Control Protocol |HTCPCP/1.0| / 4-1-1998

^[2] Wikipedia – Hyper Text Coffee Pot Control Protocol

^[3] Bugzilla – Bug 46647 – |coffeehandler| Joke: HTCPCP not supported |RFC2324| / 7-27-2000

^[4] Kurgan.org – 418 I'm a Teapot

^[5] Royal Holloway Université of London – 418 error code

^[6] The New York Times – 418

^[7] The BBC – BBC – CBeebies – Teapot

^[8] Around The Interwebs – HTTP Error Code 418 – I’m A Teapot

^[9] The Minery – HTTP Error 418: I'm a Teapot

^[10] 100pulse – HTTP Error 418 – I'm a teapot

^[11] 418 / I'm a teapot