Nginx Server Errors
Web Server — 15 error codes
Reference list of 15 Nginx server errors with meanings, common causes, and related context.
About Nginx Server Errors
Nginx handles both standard HTTP status codes (such as 500, 502, 503, and 504) and several Nginx-specific codes. The Nginx-specific codes — 444, 494, 495, 496, 497, and 499 — represent cases outside ordinary HTTP response semantics, including a connection closed without a response (444), client-certificate conditions (495 and 496), a plain request sent to an HTTPS port (497), and a client disconnect recorded by Nginx (499).
When Nginx operates as a reverse proxy, a 5xx response can reflect either proxy-layer handling or an upstream failure. The status code by itself does not establish which layer originated the response, so the collection treats these as related but distinct contexts.
This collection documents 15 Nginx error codes, covering standard HTTP codes Nginx may surface (400, 403, 411, 413, 414, 416, 500, 502, 503) alongside Nginx-specific handling codes (444, 494–497, 499). Each entry explains the code meaning and how it relates to standard HTTP behaviour.
Showing 15 of 15 error codes
Bad Gateway (Nginx) — the reverse proxy received an invalid response
Payload Too Large — the request body exceeds the size limit enforced by the server
Service Unavailable
Internal Server Error — Nginx failed while processing the request or communicating with an upstream
No Response — Nginx closed the connection without returning an HTTP response
Request Header Too Large — Nginx rejected the request because header data was too large
Client Closed Request — Nginx logged that the client closed the connection first
SSL Certificate Error — an invalid client SSL certificate was presented
SSL Certificate Required — the client failed to present an identity certificate
HTTP Request Sent to HTTPS Port — plain text sent over an encrypted channel
Bad Request — Nginx rejected the request due to malformed syntax or an oversized header
Forbidden — Nginx denied access due to insufficient file permissions or an explicit deny rule
Length Required — the server refuses the request without a valid Content-Length header
URI Too Long
Range Not Satisfiable
Frequently Asked Questions
Nginx defines non-standard codes (444, 494, 495, 496, 497, 499) for situations the HTTP specification does not cover. They include silently closing a connection (444), client-certificate conditions (495 and 496), a regular request sent to an HTTPS port (497), and a client disconnect recorded by Nginx (499).
When Nginx acts as a reverse proxy, 5xx codes can originate from either the upstream server or Nginx itself. The same status code does not, on its own, establish which layer produced the failure.
A 499 means the client closed the connection before Nginx finished sending the response. This often happens when users navigate away from a slow page, when a mobile connection drops, or when a client-side timeout fires before the backend responds.