← All status codes4xx – Client Error

HTTP 431 – Request Header Fields Too Large

The server is unwilling to process the request because its header fields are too large.

Common use case

Triggered by oversized cookies, huge JWTs stuffed into headers, or an accumulation of tracking/session headers that exceed a server or proxy's configured limit.

Example

HTTP/1.1 431 Request Header Fields Too Large

History

Standardised in RFC 6585 (2012).

Did you know?

It is a common gotcha for developers who store large amounts of data in cookies or auth tokens - the fix is usually to move that data server-side and reference it with a small ID.

Other 4xx codes

400Bad Request401Unauthorized402Payment Required403Forbidden404Not Found405Method Not Allowed406Not Acceptable407Proxy Authentication Required408Request Timeout409Conflict410Gone411Length Required412Precondition Failed413Content Too Large414URI Too Long415Unsupported Media Type416Range Not Satisfiable417Expectation Failed418I'm a teapot422Unprocessable Content425Too Early426Upgrade Required428Precondition Required429Too Many Requests430Shopify Security Rejection444No Response451Unavailable For Legal Reasons460Client Closed Connection463Malformed X-Forwarded-For Header464Incompatible Protocol Versions494Request Header Too Large495SSL Certificate Error496SSL Certificate Required497HTTP Request Sent To HTTPS Port499Client Closed Request