Request Header Too Large — Nginx rejected the request because header data was too large
What 494 Means
The 494 error on the Nginx Server-Errors indicates request header too large — nginx rejected the request because header data was too large. This typically occurs due to oversized cookie header from accumulated site data.
Nginx 494 Request Header Too Large is a non-standard code used when the request headers exceed what Nginx is willing or able to accept. It commonly appears when cookies, forwarded headers, or custom metadata grow beyond configured buffer limits. Because Nginx rejects the request at the edge, the application behind it may never see the traffic that triggered the error.
Technical Background
A 494 is closely related to header parsing and buffer limits at the web server layer. The request line and routing may be fine, but the combined header block is too large for Nginx to process safely under its current limits.
That makes 494 different from a generic 400. A 400 covers broad malformed request problems, while 494 is narrower and points specifically to header size pressure. It is also conceptually close to 431, but 494 is the Nginx-specific form many operators encounter in logs.
Common Causes
- Oversized Cookie header from accumulated site data
- Too many forwarded or authentication headers
- Duplicate proxy headers inflate total header size
- Unusually long custom header values exceed buffer limits
Typical Scenarios
- A site accumulates large cookies until returning visitors exceed the header limit
- A proxy chain adds enough forwarding headers to overflow Nginx buffers
- An integration sends unusually long custom headers for tracing or auth data
What to Know
A 494 is often limited to particular clients, browsers, or proxy paths because header growth usually comes from cookies or added metadata. When only returning users or one proxy chain trigger it, oversized headers are a stronger explanation than a broad application failure.
Frequently Asked Questions
Common questions about Nginx 494 error
The most common cause is oversized request headers, especially large cookies. Forwarding chains and long custom headers can also push the total header block beyond Nginx buffer limits.
They are closely related in meaning because both point to oversized request headers. The difference is that 494 is Nginx-specific, while 431 is the standard HTTP status most closely associated with the same condition.
Header size often depends on client-specific cookies, tokens, or proxy-added metadata. That is why the problem can affect only a subset of users or request paths.