494 Request header too large

HTTP response status code 494 Request header too large is an unofficial client error used by nginx and Akamai Enterprise Application Access (EAA). The server returns this code when the client sends an HTTP request with headers exceeding the configured buffer size.

Table of Contents

Usage
Example
How to fix
Takeaway
See also

Usage

The 494 Request header too large status code indicates the server is unwilling to process the HTTP request because the total header size or the content of one or more individual headers exceeds the allowed limit.

Note

494 Request header too large is similar to the official 431 status code.

Note

494 is an nginx-internal status code. nginx logs the error as 494 internally but returns 400 to the client unless error_page 494 is configured to map the code to a different response.

Akamai Enterprise Application Access (EAA) also returns 494 when an HTTP request header or browser cookie exceeds the configured proxy buffer value (default 4 KB). The EAA connector sits between the client and the origin application, enforcing its own buffer limits independently of the backend server configuration.

SEO impact

Search engines like Google do not index a URL with 494 Request header too large response status. URLs previously indexed with this code are removed from search results.

Example

A client sends a request with an oversized Cookie header. The nginx server rejects the request with 494 Request header too large.

Request

GET /dashboard HTTP/1.1
Host: www.example.re
Cookie: session=abc123...(4096+ bytes)

Response

HTTP/1.1 494
Content-Type: text/html
Content-Length: 168

<html>
  <head>
    <title>Request Header Too Large</title>
  </head>
  <body>
   <p>The request header is too large for the
   server to process.</p>
  </body>
</html>

How to fix

Two nginx directives control header buffer sizes. The client_header_buffer_size handles initial header reads (default 1 KB). When headers exceed this buffer, nginx falls back to large_client_header_buffers (default four buffers at 8 KB each).

Increase both values in nginx.conf under the http block:

client_header_buffer_size 4k;
large_client_header_buffers 4 16k;

A single request header line (one header name and value) must fit within a single buffer. If one Cookie header exceeds 16 KB, the buffer size needs to grow beyond 16k regardless of the buffer count.

Reload nginx after making changes:

nginx -t && systemctl reload nginx

Reduce header size on the client side. Oversized Cookie headers from runaway cookie growth are the most frequent cause. Clear unnecessary cookies, consolidate tracking cookies, and shorten custom header values.

Audit application cookie behavior. Session frameworks, analytics scripts, and advertising pixels each add cookies. A domain accumulating dozens of cookies over time pushes total header size past default limits.

For Kubernetes environments using nginx Ingress, set buffer sizes through annotations or ConfigMap entries:

nginx.ingress.kubernetes.io/client-header-buffer-size: "4k"
nginx.ingress.kubernetes.io/large-client-header-buffers: "4 16k"

For Akamai EAA, increase the Proxy Buffer Size in the Advanced tab under the Miscellaneous section for the affected application in the Enterprise Center console.

This error is functionally identical to 431 but specific to nginx and Akamai EAA internal handling.

Takeaway

The 494 Request header too large status code is a nginx client error sent when the request headers exceed the configured buffer limits.

494 Request header too large

Usage

Example

How to fix

Takeaway

See also