494 Request Header Too Large

nginx internal: request header or cookie too large; the client receives 400.

494 at a glance

Code: 494
Name: Request Header Too Large
Class: 4xx Client error
Status: Non-standard used by nginx
Documented by: nginx
Client receives: A 400 Bad Request page; 494 appears only in nginx logs and error_page.
Cacheable by default: Not applicable: this code is never sent to the client.

What 494 means

nginx uses 494 internally when a request header line exceeds large_client_header_buffers. It is logged as 494, but the client receives 400 Bad Request with the text "Request Header Or Cookie Too Large". The separate code exists so you can attach a custom page with error_page 494.

What typically causes a 494

Oversized cookies (many tracking or session cookies on a shared domain).
Very long Authorization headers (large JWTs) or Referer values.

Fix it on the server

Raise large_client_header_buffers 4 16k; if large headers are legitimate.
Better, shrink cookies and tokens; other servers (Node 16 KB, ALB, CDNs) have limits too.

Fix it as a client or visitor

Clear cookies for the domain and its parent domain.

Headers that go with 494

Header	Role
`Cookie`	The usual oversized header.

Example response

HTTP/1.1 400 Bad Request
Server: nginx
Content-Type: text/html

<center>Request Header Or Cookie Too Large</center>