There's "431 Request Header Fields Too Large" which you will see occasionally. But after that 451 is the only other 400-level error code above 429. It was chosen as a reference to the book Fahrenheit 451.

451 is kind of a novelty code, its meaning being related to Bradbury's "Fahrenheit 451" SciFi novel.

Oh! You'll love this: 418 I'm a teapot

https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/...

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