Is 418 a real status code?

It is in an Internet Standards Track RFC (sort of). It is not in mainline RFC 9110, but most HTTP libraries recognize it.

The Hyper Text Coffee Pot Control Protocol, RFC 2324. An April Fools joke from 1998 that defines BREW and WHEN methods. 418 came from there.

418 I'm a Teapot: HTTP Status Code Meaning, Causes, and Fixes

What 418 I'm a Teapot means

418 I'm a Teapot is the most famous joke status code on the web. It comes from RFC 2324, the Hyper Text Coffee Pot Control Protocol, an April Fools' RFC from 1998. Some servers return it for fun; some bot-detection systems use it as a tarpit response; it has been removed from major browsers' implementations and added back multiple times due to internet outcry. It will probably outlive us all.

When servers should return it: Return 418 only as a joke or easter egg. Real APIs should not use it.

Example response

curl -i https://www.google.com/teapot

HTTP/2 418
content-type: text/html
<html>I'm a teapot.</html>

More references

For a one-page reference of all HTTP status codes, see the HTTP cheat sheet. For testing API responses, try the API Tester tool. For inspecting responses on the command line, the curl cheat sheet covers the most common flags.