The Meaning of HTTP Status Codes

The exams are over, the holiday has begun, time to start posting again — let’s write about HTTP status first.

What Is an HTTP Status Code

An HTTP status code (HTTP Status Code) is a 3-digit code used to indicate the HTTP response status of a web server; it shows how the server handled the HTTP request.

The Five Major Classes of HTTP Status Codes

100-199: Used to specify certain actions the client should take. 200-299: Used to indicate the request succeeded. 300-399: Used for files that have moved, often included in the Location header to specify the new address. 400-499: Used to point out client errors. 500-599: Used to support server errors.

HTTP Status Code List

HTTP Status Code List

Status	English Name	Description
100	Continue	Continue. The client should continue with its request.
101	Switching Protocols	Switching protocols. The server switches protocols according to the client’s request. It can only switch to more advanced protocols, e.g., a newer version of HTTP.
200	OK	Success. Generally used for GET and POST requests.
201	Created	Created. The request succeeded and a new resource was created.
202	Accepted	Accepted. The request has been accepted but not yet processed.
203	Non-Authoritative Information	Non-authoritative information. The request succeeded, but the returned meta information is not from the original server but a copy.
204	No Content	No content. The server processed successfully but returned no content. This ensures the browser keeps displaying the current document without updating the page.
205	Reset Content	Reset content. The server processed successfully; the user agent (e.g., browser) should reset the document view. This return code can be used to clear the browser’s form fields.
206	Partial Content	Partial content. The server successfully processed part of the GET request.
300	Multiple Choices	Multiple choices. The requested resource may include multiple locations; a list of resource characteristics and addresses may be returned for the user agent (e.g., browser) to choose.
301	Moved Permanently	Moved permanently. The requested resource has been permanently moved to a new URI; the response includes the new URI, and the browser will automatically redirect to it. Any future new request should use the new URI instead.
302	Found	Temporary move. Similar to 301, but the resource is only moved temporarily. The client should keep using the original URI.
303	See Other	See other. Similar to 301. Use GET and POST requests to view.
304	Not Modified	Not modified. The requested resource was not modified. When the server returns this status code, it returns no resource. Clients usually cache visited resources, and by providing a header indicating the client only wants resources modified after a given date.
305	Use Proxy	Use proxy. The requested resource must be accessed through a proxy.
306	Unused	An obsolete HTTP status code.
307	Temporary Redirect	Temporary redirect. Similar to 302. Uses GET to redirect.
400	Bad Request	The client’s request had a syntax error the server could not understand.
401	Unauthorized	The request requires user authentication.
402	Payment Required	Reserved for future use.
403	Forbidden	The server understood the client’s request but refuses to execute it.
404	Not Found	The server could not find the resource (web page) based on the client’s request. With this code, web designers can set up a custom “requested resource not found” page.
405	Method Not Allowed	The method in the client’s request is not allowed.
406	Not Acceptable	The server could not fulfill the request based on the content characteristics requested by the client.
407	Proxy Authentication Required	The request requires proxy authentication. Similar to 401, but the requester should authorize using a proxy.
408	Request Time-out	The server waited too long for the request sent by the client and timed out.
409	Conflict	The server may return this code when completing the client’s PUT request; a conflict occurred while processing the request.
410	Gone	The resource requested by the client no longer exists. 410 differs from 404 — if a resource previously existed but is now permanently deleted, the 410 code can be used; web designers can specify the resource’s new location via the 301 code.
411	Length Required	The server cannot process the request information sent by the client without a Content-Length.
412	Precondition Failed	The precondition in the client’s request information is wrong.
413	Request Entity Too Large	The server cannot process the request because the entity is too large, so it refuses the request. To prevent repeated client requests, the server may close the connection. If the server is only temporarily unable to process it, it will include a Retry-After response.
414	Request-URI Too Large	The requested URI is too long (the URI is usually the web address), and the server cannot process it.
415	Unsupported Media Type	The server cannot process the media format attached to the request.
416	Requested range not satisfiable	The range requested by the client is invalid.
417	Expectation Failed	The server cannot satisfy the Expect request header.
500	Internal Server Error	Internal server error; the request could not be completed.
501	Not Implemented	The server does not support the requested functionality and cannot complete the request.
502	Bad Gateway	As a gateway or proxy, the server received an invalid request from the upstream server.
503	Service Unavailable	The server is temporarily unable to process the client’s request due to overload or maintenance. The duration may be included in the server’s Retry-After header.
504	Gateway Time-out	As a gateway or proxy, the server did not get the request from the upstream server in time.
505	HTTP Version not supported	The server does not support the HTTP protocol version requested and cannot complete processing.