431 Request Header Fields Too Large
4xx Client error
The headers are too large — often the result of accumulated cookies.
| On the wire | HTTP/1.1 431 Request Header Fields Too Large |
|---|---|
| Code | 431 |
| Is it an error | Yes — this is an error |
| Category | 4xx Client error |
The problem is on the request side; sending the same thing again will fail again.
How to read this
- The first digit of a status code carries the meaning: 4 means the request, 5 means the server.
- 404 means "not there"; 403 means "there, but not for you". Swapping them makes debugging slower.
- Header names are case-insensitive — Content-Type and content-type are the same header.
- Caching and CORS problems usually come down to one header line, visible in the browser’s network tab.
Frequently asked questions
Q. What does HTTP 431 Request Header Fields Too Large mean?
The headers are too large — often the result of accumulated cookies.
Q. What does 431 Request Header Fields Too Large look like on the wire?
It travels as HTTP/1.1 431 Request Header Fields Too Large
Q. Is 431 Request Header Fields Too Large an error?
Yes. A code starting with 4 blames the request; one starting with 5 blames the server.
Q. What group does 431 Request Header Fields Too Large belong to?
The 4xx client error group; the rest of that group is listed further down.