All HTTP status codes

HTTP 431 Request Header Fields Too Large

Client Error

Headers (one or all together) are too large for the server — very often a bloated Cookie header.

Defined in RFC 6585

Common causes

  • Cookies accumulated beyond proxy/server header limits
  • Excessively long Referer or custom headers

How to fix it

  1. Clear cookies for the site; shrink what your app stores in cookies

  2. Move large data out of headers

  3. Raise server header-size limits only if genuinely needed

Related status codes

400 Bad Request

The server can't or won't process the request because the client sent something malformed — invalid JSON, bad query parameters, broken headers or framing.

413 Content Too Large

The request body exceeds what the server is willing to process. Formerly called 'Payload Too Large'.

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