HTTP 418: the joke the spec had to reserve

RFC 2324, dated 1 April 1998, defines the Hyper Text Coffee Pot Control Protocol. If you try to brew coffee with a teapot, the answer is 418 I'm a teapot.

Check yourself

Can a new standard reuse 418 for something serious? Answer: not for now. RFC 9110 (June 2022), section 15.5.19, says the code was deployed as a joke so often that it's unusable for future use, and it is reserved in the IANA registry. The heading there reads 418 (Unused).

Important

The lesson is real: once a value ships and people depend on it, removing it is harder than adding it. RFC 2324 itself says it isn't a standard of any kind, and that didn't stop anyone.

Before a value ships

• ☐ Write down what is in scope
• ☐ Name who can say no
• ☐ Log decisions about public names and codes
• ☐ Check what clients already depend on

Project charter — agree the scope before it ships →

Source: rfc-editor.org, RFC 2324, section 2.3.2; RFC 9110, section 15.5.19.