This is a list of Hypertext Transfer Protocol (HTTP) response status codes. Status codes are issued by a server in response to a client's request made to the server. It includes codes from IETF Request for Comments (RFCs), other specifications, and some additional codes used in some common applications of the HTTP. The first digit of the status code specifies one of five standard classes of responses. The optional message phrases shown are typical, but any human-readable alternative may be provided, or none at all. Unless otherwise stated, the status code is part of the HTTP standard. The Internet Assigned Numbers Authority (IANA) maintains the official registry of HTTP status codes. All HTTP response status codes are separated into five classes or categories. The first digit of the status code defines the class of response, while the last two digits do not have any classifying or categorization role. There are five classes defined by the standard:

1xx informational response

An informational response indicates that the request was received and understood. It is issued on a provisional basis while request processing continues. It alerts the client to wait for a final response. The message consists only of the status line and optional header fields, and is terminated by an empty line. As the HTTP/1.0 standard did not define any 1xx status codes, servers send a 1xx response to an HTTP/1.0 compliant client except under experimental conditions.

2xx success

This class of status codes indicates the action requested by the client was received, understood, and accepted.

3xx redirection

This class of status code indicates the client must take additional action to complete the request. Many of these status codes are used in URL redirection. A user agent may carry out the additional action with no user interaction only if the method used in the second request is GET or HEAD. A user agent may automatically redirect a request. A user agent should detect and intervene to prevent cyclical redirects.

4xx client errors

This class of status code is intended for situations in which the error seems to have been caused by the client. Except when responding to a HEAD request, the server include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents display any included entity to the user.

5xx server errors

The server failed to fulfill a request. Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has encountered an error or is otherwise incapable of performing the request. Except when responding to a HEAD request, the server include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents display any included entity to the user. These response codes are applicable to any request method.

Unofficial codes

The following codes are not specified by any standard.

Internet Information Services

Microsoft's Internet Information Services (IIS) web server expands the 4xx error space to signal errors with the client's request. IIS sometimes uses additional decimal sub-codes for more specific information, however these sub-codes only appear in the response payload and in documentation, not in the place of an actual HTTP status code.

nginx

The nginx web server software expands the 4xx error space to signal issues with the client's request.

Cloudflare

Cloudflare's reverse proxy service expands the 5xx series of errors space to signal issues with the origin server.

AWS Elastic Load Balancing

Amazon Web Services' Elastic Load Balancing adds a few custom return codes to signal issues either with the client request or with the origin server.

Caching warning codes (obsoleted)

The following caching related warning codes were specified under. Unlike the other status codes above, these were not sent as the response status in the HTTP protocol, but as part of the "Warning" HTTP header. Since this "Warning" header is often neither sent by servers nor acknowledged by clients, this header and its codes were obsoleted by the HTTP Working Group in 2022 with.