What is http error codes

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From Wikipedia, the free encyclopedia

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 (RFC 9110).

The Internet Assigned Numbers Authority (IANA) maintains the official registry of HTTP status codes.[1]

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 – the request was received, continuing process
  • 2xx successful – the request was successfully received, understood, and accepted
  • 3xx redirection – further action needs to be taken in order to complete the request
  • 4xx client error – the request contains bad syntax or cannot be fulfilled
  • 5xx server error – the server failed to fulfil an apparently valid request

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 must not[note 1] send a 1xx response to an HTTP/1.0 compliant client except under experimental conditions.

100 Continue
The server has received the request headers and the client should proceed to send the request body (in the case of a request for which a body needs to be sent; for example, a POST request). Sending a large request body to a server after a request has been rejected for inappropriate headers would be inefficient. To have a server check the request’s headers, a client must send Expect: 100-continue as a header in its initial request and receive a 100 Continue status code in response before sending the body. If the client receives an error code such as 403 (Forbidden) or 405 (Method Not Allowed) then it should not send the request’s body. The response 417 Expectation Failed indicates that the request should be repeated without the Expect header as it indicates that the server does not support expectations (this is the case, for example, of HTTP/1.0 servers).[2]
101 Switching Protocols
The requester has asked the server to switch protocols and the server has agreed to do so.
102 Processing (WebDAV; RFC 2518)
A WebDAV request may contain many sub-requests involving file operations, requiring a long time to complete the request. This code indicates that the server has received and is processing the request, but no response is available yet.[3] This prevents the client from timing out and assuming the request was lost.
103 Early Hints (RFC 8297)
Used to return some response headers before final HTTP message.[4]

2xx success

This class of status codes indicates the action requested by the client was received, understood, and accepted.[1]

200 OK
Standard response for successful HTTP requests. The actual response will depend on the request method used. In a GET request, the response will contain an entity corresponding to the requested resource. In a POST request, the response will contain an entity describing or containing the result of the action.
201 Created
The request has been fulfilled, resulting in the creation of a new resource.[5]
202 Accepted
The request has been accepted for processing, but the processing has not been completed. The request might or might not be eventually acted upon, and may be disallowed when processing occurs.
203 Non-Authoritative Information (since HTTP/1.1)
The server is a transforming proxy (e.g. a Web accelerator) that received a 200 OK from its origin, but is returning a modified version of the origin’s response.[6][7]
204 No Content
The server successfully processed the request, and is not returning any content.
205 Reset Content
The server successfully processed the request, asks that the requester reset its document view, and is not returning any content.
206 Partial Content
The server is delivering only part of the resource (byte serving) due to a range header sent by the client. The range header is used by HTTP clients to enable resuming of interrupted downloads, or split a download into multiple simultaneous streams.
207 Multi-Status (WebDAV; RFC 4918)
The message body that follows is by default an XML message and can contain a number of separate response codes, depending on how many sub-requests were made.[8]
208 Already Reported (WebDAV; RFC 5842)
The members of a DAV binding have already been enumerated in a preceding part of the (multistatus) response, and are not being included again.
226 IM Used (RFC 3229)
The server has fulfilled a request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.[9]

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.[1]

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.[10]

300 Multiple Choices
Indicates multiple options for the resource from which the client may choose (via agent-driven content negotiation). For example, this code could be used to present multiple video format options, to list files with different filename extensions, or to suggest word-sense disambiguation.
301 Moved Permanently
This and all future requests should be directed to the given URI.
302 Found (Previously «Moved temporarily»)
Tells the client to look at (browse to) another URL. The HTTP/1.0 specification (RFC 1945) required the client to perform a temporary redirect with the same method (the original describing phrase was «Moved Temporarily»),[11] but popular browsers implemented 302 redirects by changing the method to GET. Therefore, HTTP/1.1 added status codes 303 and 307 to distinguish between the two behaviours.[10]
303 See Other (since HTTP/1.1)
The response to the request can be found under another URI using the GET method. When received in response to a POST (or PUT/DELETE), the client should presume that the server has received the data and should issue a new GET request to the given URI.
304 Not Modified
Indicates that the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match. In such case, there is no need to retransmit the resource since the client still has a previously-downloaded copy.
305 Use Proxy (since HTTP/1.1)
The requested resource is available only through a proxy, the address for which is provided in the response. For security reasons, many HTTP clients (such as Mozilla Firefox and Internet Explorer) do not obey this status code.
306 Switch Proxy
No longer used. Originally meant «Subsequent requests should use the specified proxy.»
307 Temporary Redirect (since HTTP/1.1)
In this case, the request should be repeated with another URI; however, future requests should still use the original URI. In contrast to how 302 was historically implemented, the request method is not allowed to be changed when reissuing the original request. For example, a POST request should be repeated using another POST request.
308 Permanent Redirect
This and all future requests should be directed to the given URI. 308 parallel the behaviour of 301, but does not allow the HTTP method to change. So, for example, submitting a form to a permanently redirected resource may continue smoothly.

4xx client errors

A The Wikimedia 404 message

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 should 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 should display any included entity to the user.

400 Bad Request
The server cannot or will not process the request due to an apparent client error (e.g., malformed request syntax, size too large, invalid request message framing, or deceptive request routing).
401 Unauthorized
Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource. See Basic access authentication and Digest access authentication. 401 semantically means «unauthorised», the user does not have valid authentication credentials for the target resource.
Some sites incorrectly issue HTTP 401 when an IP address is banned from the website (usually the website domain) and that specific address is refused permission to access a website.[citation needed]
402 Payment Required
Reserved for future use. The original intention was that this code might be used as part of some form of digital cash or micropayment scheme, as proposed, for example, by GNU Taler,[13] but that has not yet happened, and this code is not widely used. Google Developers API uses this status if a particular developer has exceeded the daily limit on requests.[14] Sipgate uses this code if an account does not have sufficient funds to start a call.[15] Shopify uses this code when the store has not paid their fees and is temporarily disabled.[16] Stripe uses this code for failed payments where parameters were correct, for example blocked fraudulent payments.[17]
403 Forbidden
The request contained valid data and was understood by the server, but the server is refusing action. This may be due to the user not having the necessary permissions for a resource or needing an account of some sort, or attempting a prohibited action (e.g. creating a duplicate record where only one is allowed). This code is also typically used if the request provided authentication by answering the WWW-Authenticate header field challenge, but the server did not accept that authentication. The request should not be repeated.
404 Not Found
The requested resource could not be found but may be available in the future. Subsequent requests by the client are permissible.
405 Method Not Allowed
A request method is not supported for the requested resource; for example, a GET request on a form that requires data to be presented via POST, or a PUT request on a read-only resource.
406 Not Acceptable
The requested resource is capable of generating only content not acceptable according to the Accept headers sent in the request. See Content negotiation.
407 Proxy Authentication Required
The client must first authenticate itself with the proxy.
408 Request Timeout
The server timed out waiting for the request. According to HTTP specifications: «The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.»
409 Conflict
Indicates that the request could not be processed because of conflict in the current state of the resource, such as an edit conflict between multiple simultaneous updates.
410 Gone
Indicates that the resource requested was previously in use but is no longer available and will not be available again. This should be used when a resource has been intentionally removed and the resource should be purged. Upon receiving a 410 status code, the client should not request the resource in the future. Clients such as search engines should remove the resource from their indices. Most use cases do not require clients and search engines to purge the resource, and a «404 Not Found» may be used instead.
411 Length Required
The request did not specify the length of its content, which is required by the requested resource.
412 Precondition Failed
The server does not meet one of the preconditions that the requester put on the request header fields.
413 Payload Too Large
The request is larger than the server is willing or able to process. Previously called «Request Entity Too Large» in RFC 2616.[18]
414 URI Too Long
The URI provided was too long for the server to process. Often the result of too much data being encoded as a query-string of a GET request, in which case it should be converted to a POST request. Called «Request-URI Too Long» previously in RFC 2616.[19]
415 Unsupported Media Type
The request entity has a media type which the server or resource does not support. For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format.
416 Range Not Satisfiable
The client has asked for a portion of the file (byte serving), but the server cannot supply that portion. For example, if the client asked for a part of the file that lies beyond the end of the file. Called «Requested Range Not Satisfiable» previously RFC 2616.[20]
417 Expectation Failed
The server cannot meet the requirements of the Expect request-header field.[21]
418 I’m a teapot (RFC 2324, RFC 7168)
This code was defined in 1998 as one of the traditional IETF April Fools’ jokes, in RFC 2324, Hyper Text Coffee Pot Control Protocol, and is not expected to be implemented by actual HTTP servers. The RFC specifies this code should be returned by teapots requested to brew coffee.[22] This HTTP status is used as an Easter egg in some websites, such as Google.com’s «I’m a teapot» easter egg.[23][24][25] Sometimes, this status code is also used as a response to a blocked request, instead of the more appropriate 403 Forbidden.[26][27]
421 Misdirected Request
The request was directed at a server that is not able to produce a response (for example because of connection reuse).
422 Unprocessable Entity
The request was well-formed but was unable to be followed due to semantic errors.[8]
423 Locked (WebDAV; RFC 4918)
The resource that is being accessed is locked.[8]
424 Failed Dependency (WebDAV; RFC 4918)
The request failed because it depended on another request and that request failed (e.g., a PROPPATCH).[8]
425 Too Early (RFC 8470)
Indicates that the server is unwilling to risk processing a request that might be replayed.
426 Upgrade Required
The client should switch to a different protocol such as TLS/1.3, given in the Upgrade header field.
428 Precondition Required (RFC 6585)
The origin server requires the request to be conditional. Intended to prevent the ‘lost update’ problem, where a client GETs a resource’s state, modifies it, and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.[28]
429 Too Many Requests (RFC 6585)
The user has sent too many requests in a given amount of time. Intended for use with rate-limiting schemes.[28]
431 Request Header Fields Too Large (RFC 6585)
The server is unwilling to process the request because either an individual header field, or all the header fields collectively, are too large.[28]
451 Unavailable For Legal Reasons (RFC 7725)
A server operator has received a legal demand to deny access to a resource or to a set of resources that includes the requested resource.[29] The code 451 was chosen as a reference to the novel Fahrenheit 451 (see the Acknowledgements in the RFC).

5xx server errors

The server failed to fulfil 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 should include an entity containing an explanation of the error situation, and indicate whether it is a temporary or permanent condition. Likewise, user agents should display any included entity to the user. These response codes are applicable to any request method.

500 Internal Server Error
A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.
501 Not Implemented
The server either does not recognize the request method, or it lacks the ability to fulfil the request. Usually this implies future availability (e.g., a new feature of a web-service API).
502 Bad Gateway
The server was acting as a gateway or proxy and received an invalid response from the upstream server.
503 Service Unavailable
The server cannot handle the request (because it is overloaded or down for maintenance). Generally, this is a temporary state.[30]
504 Gateway Timeout
The server was acting as a gateway or proxy and did not receive a timely response from the upstream server.
505 HTTP Version Not Supported
The server does not support the HTTP version used in the request.
506 Variant Also Negotiates (RFC 2295)
Transparent content negotiation for the request results in a circular reference.[31]
507 Insufficient Storage (WebDAV; RFC 4918)
The server is unable to store the representation needed to complete the request.[8]
508 Loop Detected (WebDAV; RFC 5842)
The server detected an infinite loop while processing the request (sent instead of 208 Already Reported).
510 Not Extended (RFC 2774)
Further extensions to the request are required for the server to fulfill it.[32]
511 Network Authentication Required (RFC 6585)
The client needs to authenticate to gain network access. Intended for use by intercepting proxies used to control access to the network (e.g., «captive portals» used to require agreement to Terms of Service before granting full Internet access via a Wi-Fi hotspot).[28]

Unofficial codes

The following codes are not specified by any standard.

419 Page Expired (Laravel Framework)
Used by the Laravel Framework when a CSRF Token is missing or expired.
420 Method Failure (Spring Framework)
A deprecated response used by the Spring Framework when a method has failed.[33]
420 Enhance Your Calm (Twitter)
Returned by version 1 of the Twitter Search and Trends API when the client is being rate limited; versions 1.1 and later use the 429 Too Many Requests response code instead.[34] The phrase «Enhance your calm» comes from the 1993 movie Demolition Man, and its association with this number is likely a reference to cannabis.[citation needed]
430 Request Header Fields Too Large (Shopify)
Used by Shopify, instead of the 429 Too Many Requests response code, when too many URLs are requested within a certain time frame.[35]
450 Blocked by Windows Parental Controls (Microsoft)
The Microsoft extension code indicated when Windows Parental Controls are turned on and are blocking access to the requested webpage.[36]
498 Invalid Token (Esri)
Returned by ArcGIS for Server. Code 498 indicates an expired or otherwise invalid token.[37]
499 Token Required (Esri)
Returned by ArcGIS for Server. Code 499 indicates that a token is required but was not submitted.[37]
509 Bandwidth Limit Exceeded (Apache Web Server/cPanel)
The server has exceeded the bandwidth specified by the server administrator; this is often used by shared hosting providers to limit the bandwidth of customers.[38]
529 Site is overloaded
Used by Qualys in the SSLLabs server testing API to signal that the site can’t process the request.[39]
530 Site is frozen
Used by the Pantheon Systems web platform to indicate a site that has been frozen due to inactivity.[40]
598 (Informal convention) Network read timeout error
Used by some HTTP proxies to signal a network read timeout behind the proxy to a client in front of the proxy.[41]
599 Network Connect Timeout Error
An error used by some HTTP proxies to signal a network connect timeout behind the proxy to a client in front of the proxy.

Internet Information Services

Microsoft’s Internet Information Services (IIS) web server expands the 4xx error space to signal errors with the client’s request.

440 Login Time-out
The client’s session has expired and must log in again.[42]
449 Retry With
The server cannot honour the request because the user has not provided the required information.[43]
451 Redirect
Used in Exchange ActiveSync when either a more efficient server is available or the server cannot access the users’ mailbox.[44] The client is expected to re-run the HTTP AutoDiscover operation to find a more appropriate server.[45]

IIS sometimes uses additional decimal sub-codes for more specific information,[46] 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.[47][48]

444 No Response
Used internally[49] to instruct the server to return no information to the client and close the connection immediately.
494 Request header too large
Client sent too large request or too long header line.
495 SSL Certificate Error
An expansion of the 400 Bad Request response code, used when the client has provided an invalid client certificate.
496 SSL Certificate Required
An expansion of the 400 Bad Request response code, used when a client certificate is required but not provided.
497 HTTP Request Sent to HTTPS Port
An expansion of the 400 Bad Request response code, used when the client has made a HTTP request to a port listening for HTTPS requests.
499 Client Closed Request
Used when the client has closed the request before the server could send a response.

Cloudflare

Cloudflare’s reverse proxy service expands the 5xx series of errors space to signal issues with the origin server.[50]

520 Web Server Returned an Unknown Error
The origin server returned an empty, unknown, or unexpected response to Cloudflare.[51]
521 Web Server Is Down
The origin server refused connections from Cloudflare. Security solutions at the origin may be blocking legitimate connections from certain Cloudflare IP addresses.
522 Connection Timed Out
Cloudflare timed out contacting the origin server.
523 Origin Is Unreachable
Cloudflare could not reach the origin server; for example, if the DNS records for the origin server are incorrect or missing.
524 A Timeout Occurred
Cloudflare was able to complete a TCP connection to the origin server, but did not receive a timely HTTP response.
525 SSL Handshake Failed
Cloudflare could not negotiate a SSL/TLS handshake with the origin server.
526 Invalid SSL Certificate
Cloudflare could not validate the SSL certificate on the origin web server. Also used by Cloud Foundry’s gorouter.
527 Railgun Error
Error 527 indicates an interrupted connection between Cloudflare and the origin server’s Railgun server.[52]
530
Error 530 is returned along with a 1xxx error.[53]

AWS Elastic Load Balancer

Amazon’s Elastic Load Balancing adds a few custom return codes

460
Client closed the connection with the load balancer before the idle timeout period elapsed. Typically when client timeout is sooner than the Elastic Load Balancer’s timeout.[54]
463
The load balancer received an X-Forwarded-For request header with more than 30 IP addresses.[54]
561 Unauthorized
An error around authentication returned by a server registered with a load balancer. You configured a listener rule to authenticate users, but the identity provider (IdP) returned an error code when authenticating the user.[55]

Caching warning codes (obsoleted)

The following caching related warning codes were specified under RFC 7234. 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.[56][57]

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 RFC 9111.[58]

110 Response is Stale
The response provided by a cache is stale (the content’s age exceeds a maximum age set by a Cache-Control header or heuristically chosen lifetime).
111 Revalidation Failed
The cache was unable to validate the response, due to an inability to reach the origin server.
112 Disconnected Operation
The cache is intentionally disconnected from the rest of the network.
113 Heuristic Expiration
The cache heuristically chose a freshness lifetime greater than 24 hours and the response’s age is greater than 24 hours.
199 Miscellaneous Warning
Arbitrary, non-specific warning. The warning text may be logged or presented to the user.
214 Transformation Applied
Added by a proxy if it applies any transformation to the representation, such as changing the content encoding, media type or the like.
299 Miscellaneous Persistent Warning
Same as 199, but indicating a persistent warning.

See also

  • Custom error pages
  • List of FTP server return codes
  • List of HTTP header fields
  • List of SMTP server return codes
  • Common Log Format

Explanatory notes

  1. ^ Emphasised words and phrases such as must and should represent interpretation guidelines as given by RFC 2119

References

  1. ^ a b c «Hypertext Transfer Protocol (HTTP) Status Code Registry». Iana.org. Archived from the original on December 11, 2011. Retrieved January 8, 2015.
  2. ^ «RFC 9110: HTTP Semantics and Content, Section 10.1.1 «Expect»«.
  3. ^ Goland, Yaronn; Whitehead, Jim; Faizi, Asad; Carter, Steve R.; Jensen, Del (February 1999). HTTP Extensions for Distributed Authoring – WEBDAV. IETF. doi:10.17487/RFC2518. RFC 2518. Retrieved October 24, 2009.
  4. ^ Oku, Kazuho (December 2017). An HTTP Status Code for Indicating Hints. IETF. doi:10.17487/RFC8297. RFC 8297. Retrieved December 20, 2017.
  5. ^ Stewart, Mark; djna. «Create request with POST, which response codes 200 or 201 and content». Stack Overflow. Archived from the original on October 11, 2016. Retrieved October 16, 2015.
  6. ^ «RFC 9110: HTTP Semantics and Content, Section 15.3.4».
  7. ^ «RFC 9110: HTTP Semantics and Content, Section 7.7».
  8. ^ a b c d e Dusseault, Lisa, ed. (June 2007). HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV). IETF. doi:10.17487/RFC4918. RFC 4918. Retrieved October 24, 2009.
  9. ^ Delta encoding in HTTP. IETF. January 2002. doi:10.17487/RFC3229. RFC 3229. Retrieved February 25, 2011.
  10. ^ a b «RFC 9110: HTTP Semantics and Content, Section 15.4 «Redirection 3xx»«.
  11. ^ Berners-Lee, Tim; Fielding, Roy T.; Nielsen, Henrik Frystyk (May 1996). Hypertext Transfer Protocol – HTTP/1.0. IETF. doi:10.17487/RFC1945. RFC 1945. Retrieved October 24, 2009.
  12. ^ «The GNU Taler tutorial for PHP Web shop developers 0.4.0». docs.taler.net. Archived from the original on November 8, 2017. Retrieved October 29, 2017.
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  15. ^ «Shopify Documentation». Archived from the original on July 25, 2018. Retrieved July 25, 2018.
  16. ^ «Stripe API Reference – Errors». stripe.com. Retrieved October 28, 2019.
  17. ^ «RFC2616 on status 413». Tools.ietf.org. Archived from the original on March 7, 2011. Retrieved November 11, 2015.
  18. ^ «RFC2616 on status 414». Tools.ietf.org. Archived from the original on March 7, 2011. Retrieved November 11, 2015.
  19. ^ «RFC2616 on status 416». Tools.ietf.org. Archived from the original on March 7, 2011. Retrieved November 11, 2015.
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  21. ^ Larry Masinter (April 1, 1998). Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0). doi:10.17487/RFC2324. RFC 2324. Any attempt to brew coffee with a teapot should result in the error code «418 I’m a teapot». The resulting entity body MAY be short and stout.
  22. ^ I’m a teapot
  23. ^ Barry Schwartz (August 26, 2014). «New Google Easter Egg For SEO Geeks: Server Status 418, I’m A Teapot». Search Engine Land. Archived from the original on November 15, 2015. Retrieved November 4, 2015.
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  26. ^ «I Went to a Russian Website and All I Got Was This Lousy Teapot». PCMag. Retrieved December 18, 2022.
  27. ^ a b c d Nottingham, M.; Fielding, R. (April 2012). «RFC 6585 – Additional HTTP Status Codes». Request for Comments. Internet Engineering Task Force. Archived from the original on May 4, 2012. Retrieved May 1, 2012.
  28. ^ Bray, T. (February 2016). «An HTTP Status Code to Report Legal Obstacles». ietf.org. Archived from the original on March 4, 2016. Retrieved March 7, 2015.
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  31. ^ Nielsen, Henrik Frystyk; Leach, Paul; Lawrence, Scott (February 2000). An HTTP Extension Framework. IETF. doi:10.17487/RFC2774. RFC 2774. Retrieved October 24, 2009.
  32. ^ «Enum HttpStatus». Spring Framework. org.springframework.http. Archived from the original on October 25, 2015. Retrieved October 16, 2015.
  33. ^ «Twitter Error Codes & Responses». Twitter. 2014. Archived from the original on September 27, 2017. Retrieved January 20, 2014.
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  38. ^ «SSL Labs API v3 Documentation». github.com.
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  40. ^ «HTTP status codes — ascii-code.com». www.ascii-code.com. Archived from the original on January 7, 2017. Retrieved December 23, 2016.
  41. ^
    «Error message when you try to log on to Exchange 2007 by using Outlook Web Access: «440 Login Time-out»«. Microsoft. 2010. Retrieved November 13, 2013.
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  43. ^ «MS-ASCMD, Section 3.1.5.2.2». Msdn.microsoft.com. Archived from the original on March 26, 2015. Retrieved January 8, 2015.
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  47. ^ «ngx_http_special_response.c». nginx 1.9.5 source code. nginx inc. Archived from the original on May 8, 2018. Retrieved January 9, 2016.
  48. ^ «return» directive Archived March 1, 2018, at the Wayback Machine (http_rewrite module) documentation.
  49. ^ «Troubleshooting: Error Pages». Cloudflare. Archived from the original on March 4, 2016. Retrieved January 9, 2016.
  50. ^ «Error 520: web server returns an unknown error». Cloudflare. Retrieved November 1, 2019.
  51. ^ «527 Error: Railgun Listener to origin error». Cloudflare. Archived from the original on October 13, 2016. Retrieved October 12, 2016.
  52. ^ «Error 530». Cloudflare. Retrieved November 1, 2019.
  53. ^ a b «Troubleshoot Your Application Load Balancers – Elastic Load Balancing». docs.aws.amazon.com. Retrieved August 27, 2019.
  54. ^ «Troubleshoot your Application Load Balancers — Elastic Load Balancing». docs.aws.amazon.com. Retrieved January 24, 2021.
  55. ^ «Hypertext Transfer Protocol (HTTP/1.1): Caching». datatracker.ietf.org. Retrieved September 25, 2021.
  56. ^ «Warning — HTTP | MDN». developer.mozilla.org. Retrieved August 15, 2021. CC BY-SA icon.svg Some text was copied from this source, which is available under a Creative Commons Attribution-ShareAlike 2.5 Generic (CC BY-SA 2.5) license.
  57. ^ «RFC 9111: HTTP Caching, Section 5.5 «Warning»«. June 2022.

External links

  • «RFC 9110: HTTP Semantics and Content, Section 15 «Status Codes»«.
  • Hypertext Transfer Protocol (HTTP) Status Code Registry
Источник

HTTP response status codes indicate whether a specific HTTP request has been successfully completed.
Responses are grouped in five classes:

  1. Informational responses (100 – 199)
  2. Successful responses (200 – 299)
  3. Redirection messages (300 – 399)
  4. Client error responses (400 – 499)
  5. Server error responses (500 – 599)

The status codes listed below are defined by RFC 9110.

Note: If you receive a response that is not in this list, it is a non-standard response, possibly custom to the server’s software.

Information responses

100 Continue

This interim response indicates that the client should continue the request or ignore the response if the request is already finished.

101 Switching Protocols

This code is sent in response to an Upgrade request header from the client and indicates the protocol the server is switching to.

102 Processing (WebDAV)

This code indicates that the server has received and is processing the request, but no response is available yet.

103 Early Hints

This status code is primarily intended to be used with the Link header, letting the user agent start preloading resources while the server prepares a response.

Successful responses

200 OK

The request succeeded. The result meaning of «success» depends on the HTTP method:

  • GET: The resource has been fetched and transmitted in the message body.
  • HEAD: The representation headers are included in the response without any message body.
  • PUT or POST: The resource describing the result of the action is transmitted in the message body.
  • TRACE: The message body contains the request message as received by the server.
201 Created

The request succeeded, and a new resource was created as a result. This is typically the response sent after POST requests, or some PUT requests.

202 Accepted

The request has been received but not yet acted upon.
It is noncommittal, since there is no way in HTTP to later send an asynchronous response indicating the outcome of the request.
It is intended for cases where another process or server handles the request, or for batch processing.

This response code means the returned metadata is not exactly the same as is available from the origin server, but is collected from a local or a third-party copy.
This is mostly used for mirrors or backups of another resource.
Except for that specific case, the 200 OK response is preferred to this status.

204 No Content

There is no content to send for this request, but the headers may be useful.
The user agent may update its cached headers for this resource with the new ones.

205 Reset Content

Tells the user agent to reset the document which sent this request.

206 Partial Content

This response code is used when the Range header is sent from the client to request only part of a resource.

207 Multi-Status (WebDAV)

Conveys information about multiple resources, for situations where multiple status codes might be appropriate.

208 Already Reported (WebDAV)

Used inside a <dav:propstat> response element to avoid repeatedly enumerating the internal members of multiple bindings to the same collection.

226 IM Used (HTTP Delta encoding)

The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.

Redirection messages

300 Multiple Choices

The request has more than one possible response. The user agent or user should choose one of them. (There is no standardized way of choosing one of the responses, but HTML links to the possibilities are recommended so the user can pick.)

301 Moved Permanently

The URL of the requested resource has been changed permanently. The new URL is given in the response.

302 Found

This response code means that the URI of requested resource has been changed temporarily.
Further changes in the URI might be made in the future. Therefore, this same URI should be used by the client in future requests.

303 See Other

The server sent this response to direct the client to get the requested resource at another URI with a GET request.

304 Not Modified

This is used for caching purposes.
It tells the client that the response has not been modified, so the client can continue to use the same cached version of the response.

305 Use Proxy
Deprecated

Defined in a previous version of the HTTP specification to indicate that a requested response must be accessed by a proxy.
It has been deprecated due to security concerns regarding in-band configuration of a proxy.

306 unused

This response code is no longer used; it is just reserved. It was used in a previous version of the HTTP/1.1 specification.

307 Temporary Redirect

The server sends this response to direct the client to get the requested resource at another URI with same method that was used in the prior request.
This has the same semantics as the 302 Found HTTP response code, with the exception that the user agent must not change the HTTP method used: if a POST was used in the first request, a POST must be used in the second request.

308 Permanent Redirect

This means that the resource is now permanently located at another URI, specified by the Location: HTTP Response header.
This has the same semantics as the 301 Moved Permanently HTTP response code, with the exception that the user agent must not change the HTTP method used: if a POST was used in the first request, a POST must be used in the second request.

Client error responses

400 Bad Request

The server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

401 Unauthorized

Although the HTTP standard specifies «unauthorized», semantically this response means «unauthenticated».
That is, the client must authenticate itself to get the requested response.

402 Payment Required
Experimental

This response code is reserved for future use.
The initial aim for creating this code was using it for digital payment systems, however this status code is used very rarely and no standard convention exists.

403 Forbidden

The client does not have access rights to the content; that is, it is unauthorized, so the server is refusing to give the requested resource.
Unlike 401 Unauthorized, the client’s identity is known to the server.

404 Not Found

The server cannot find the requested resource.
In the browser, this means the URL is not recognized.
In an API, this can also mean that the endpoint is valid but the resource itself does not exist.
Servers may also send this response instead of 403 Forbidden to hide the existence of a resource from an unauthorized client.
This response code is probably the most well known due to its frequent occurrence on the web.

405 Method Not Allowed

The request method is known by the server but is not supported by the target resource.
For example, an API may not allow calling DELETE to remove a resource.

406 Not Acceptable

This response is sent when the web server, after performing server-driven content negotiation, doesn’t find any content that conforms to the criteria given by the user agent.

407 Proxy Authentication Required

This is similar to 401 Unauthorized but authentication is needed to be done by a proxy.

408 Request Timeout

This response is sent on an idle connection by some servers, even without any previous request by the client.
It means that the server would like to shut down this unused connection.
This response is used much more since some browsers, like Chrome, Firefox 27+, or IE9, use HTTP pre-connection mechanisms to speed up surfing.
Also note that some servers merely shut down the connection without sending this message.

409 Conflict

This response is sent when a request conflicts with the current state of the server.

410 Gone

This response is sent when the requested content has been permanently deleted from server, with no forwarding address.
Clients are expected to remove their caches and links to the resource.
The HTTP specification intends this status code to be used for «limited-time, promotional services».
APIs should not feel compelled to indicate resources that have been deleted with this status code.

411 Length Required

Server rejected the request because the Content-Length header field is not defined and the server requires it.

412 Precondition Failed

The client has indicated preconditions in its headers which the server does not meet.

413 Payload Too Large

Request entity is larger than limits defined by server.
The server might close the connection or return an Retry-After header field.

414 URI Too Long

The URI requested by the client is longer than the server is willing to interpret.

415 Unsupported Media Type

The media format of the requested data is not supported by the server, so the server is rejecting the request.

416 Range Not Satisfiable

The range specified by the Range header field in the request cannot be fulfilled.
It’s possible that the range is outside the size of the target URI’s data.

417 Expectation Failed

This response code means the expectation indicated by the Expect request header field cannot be met by the server.

418 I'm a teapot

The server refuses the attempt to brew coffee with a teapot.

421 Misdirected Request

The request was directed at a server that is not able to produce a response.
This can be sent by a server that is not configured to produce responses for the combination of scheme and authority that are included in the request URI.

422 Unprocessable Entity (WebDAV)

The request was well-formed but was unable to be followed due to semantic errors.

423 Locked (WebDAV)

The resource that is being accessed is locked.

424 Failed Dependency (WebDAV)

The request failed due to failure of a previous request.

425 Too Early
Experimental

Indicates that the server is unwilling to risk processing a request that might be replayed.

426 Upgrade Required

The server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades to a different protocol.
The server sends an Upgrade header in a 426 response to indicate the required protocol(s).

428 Precondition Required

The origin server requires the request to be conditional.
This response is intended to prevent the ‘lost update’ problem, where a client GETs a resource’s state, modifies it and PUTs it back to the server, when meanwhile a third party has modified the state on the server, leading to a conflict.

429 Too Many Requests

The user has sent too many requests in a given amount of time («rate limiting»).

The server is unwilling to process the request because its header fields are too large.
The request may be resubmitted after reducing the size of the request header fields.

451 Unavailable For Legal Reasons

The user agent requested a resource that cannot legally be provided, such as a web page censored by a government.

Server error responses

500 Internal Server Error

The server has encountered a situation it does not know how to handle.

501 Not Implemented

The request method is not supported by the server and cannot be handled. The only methods that servers are required to support (and therefore that must not return this code) are GET and HEAD.

502 Bad Gateway

This error response means that the server, while working as a gateway to get a response needed to handle the request, got an invalid response.

503 Service Unavailable

The server is not ready to handle the request.
Common causes are a server that is down for maintenance or that is overloaded.
Note that together with this response, a user-friendly page explaining the problem should be sent.
This response should be used for temporary conditions and the Retry-After HTTP header should, if possible, contain the estimated time before the recovery of the service.
The webmaster must also take care about the caching-related headers that are sent along with this response, as these temporary condition responses should usually not be cached.

504 Gateway Timeout

This error response is given when the server is acting as a gateway and cannot get a response in time.

505 HTTP Version Not Supported

The HTTP version used in the request is not supported by the server.

506 Variant Also Negotiates

The server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself, and is therefore not a proper end point in the negotiation process.

507 Insufficient Storage (WebDAV)

The method could not be performed on the resource because the server is unable to store the representation needed to successfully complete the request.

508 Loop Detected (WebDAV)

The server detected an infinite loop while processing the request.

510 Not Extended

Further extensions to the request are required for the server to fulfill it.

511 Network Authentication Required

Indicates that the client needs to authenticate to gain network access.

Browser compatibility

BCD tables only load in the browser

See also

Источник

HTTP status codes are three-digit responses from the server to the browser-side request. Everyone has probably gotten the classic 404 page-not-found error. That is an HTTP client error status code and there are a lot more of them.

These status codes (also called response status codes) serve as a means of communication between the server and the internet browser and there are multiple code classes based on the type of information they are communicating. The differences in classes are indicated through the first digit of the error code, for example: just like a 404, any other 4xx will mean that in some way the page or website could not be reached, while a 2xx means that your request was successfully completed.

Table of content

  • What are HTTP status codes?
  • How are HTTP status codes categorized?
  • Complete list of HTTP Status Codes
  • What does this HTTP status code mean?
  • HTTP Status codes to know for SEO
  • How to check the HTTP status code
  • How to fix 404 errors
  • How to fix 503 errors

How are HTTP status codes categorized?

HTTP status codes are split into 5 different categories. Each category will give you hints as to what the response was, even if you don’t know the specific response code.

For an explanation of each category — and each individual status code — click on the corresponding link below or go to our complete list of HTTP status codes.

  • 1xx — Informational: The server has received the request and is continuing the process 
  • 2xx — Successful: The request was successful and the browser has received the expected information 
  • 3xx (Redirection): You have been redirected and the completion of the request requires further action
  • 4xx (Client Error): The website or the page could not be reached, either the page is unavailable or the request contains bad syntax 
  • 5xx (Server Error): While the request appears to be valid, the server could not complete the request

Woman with a thought bubble

Complete list of HTTP Status Codes

Status code Meaning
1xx Informational  
100 Continue
101 Switching protocols
102 Processing
103 Early Hints
   
2xx Succesful  
200 OK
201 Created
202 Accepted
203  Non-Authoritative Information
204 No Content
205 Reset Content
206 Partial Content
207 Multi-Status
208 Already Reported
226 IM Used
   
3xx Redirection  
300 Multiple Choices
301 Moved Permanently
302 Found (Previously «Moved Temporarily»)
303 See Other
304 Not Modified
305 Use Proxy
306 Switch Proxy
307 Temporary Redirect
308 Permanent Redirect
   
4xx Client Error  
400 Bad Request
401 Unauthorized
402 Payment Required
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
408 Request Timeout
409 Conflict
410 Gone
411 Length Required
412 Precondition Failed
413 Payload Too Large
414 URI Too Long
415 Unsupported Media Type
416 Range Not Satisfiable
417 Expectation Failed
418 I’m a Teapot
421 Misdirected Request
422 Unprocessable Entity
423 Locked
424 Failed Dependency
425 Too Early
426 Upgrade Required
428 Precondition Required
429 Too Many Requests
431 Request Header Fields Too Large
451 Unavailable For Legal Reasons
   
5xx Server Error  
500 Internal Server Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
505 HTTP Version Not Supported
506 Variant Also Negotiates
507 Insufficient Storage
508 Loop Detected
510 Not Extended
511 Network Authentication Required

HTTP Status Codes explained individually

In some cases a HTTP response code might be descriptive enough to understand its meaning. 200 OK probably means that everything went okay. But what about a 103 Early Hints, 205 Reset Content and 305 Use Proxy?

Below is an explanation for all 63 status codes, sorted in the 5 overall categories.

What does a 1xx Informational status code mean?

A 1xx Informational status code means that the server has received the request and is continuing the process. A 1xx status code is purely temporary and is given while the request processing continues. For most tasks you won’t encounter these much, as it’s not the final response to the request.

  • 100 Continue
  • 101 Switching protocols
  • 102 Processing
  • 103 Early Hints

What does 100 Continue mean?

The 100 Continue status code means that the initial part of the request has been received by the server and that the client should proceed with the request or ignore the response if the request has already finished.

What does 101 Switching protocols mean?

The 101 Switching protocols status code means that the server understands the Upgrade header field request and indicates which protocol it is switching to.

What does 102 Processing mean?

The 102 Processing status code means that the server has accepted the full request but has not yet completed it and no response is available as of yet.

What does 103 Early Hints mean?

The 103 Early hints status code is intended to be used to allow the user agent to preload resources, while the server prepares a response. It is intended to be primarily used with the Link Header.

What does a 2xx Succesful status code mean?

A 2xx Succesful status code means that the request was successful and the browser has received the expected information. This is generally the one you want to see, as it means that the request was a success and has been received, understood and accepted it. As a website owner you should make sure that all pages and resources (images, videos, etc.) all return a 2xx status code. This means that browsers can reach it successfully and that your website visitors can see and use your website.

  • 200 OK
  • 201 Created
  • 202 Accepted
  • 203 Non-Authoritative Information
  • 204 No Content
  • 205 Reset Content
  • 206 Partial Content
  • 207 Multi-Status
  • 208 Already Reported
  • 226 IM Used

What does 200 OK mean?

The 200 OK status code means that the request was successful, but the meaning of success depends on the request method used:

  • GET: The requested resource has been fetched and transmitted to the message body.
  • HEAD: The header fields from the requested resource are sent in without the message body. 
  • POST or PUT: A description of the result of the action is transmitted to the message body.
  • TRACE: The request messages, as received by the server, will be included in the message body

When looking at things SEO-wise the 200 OK response code is the perfect status code for a functioning page, all the linked pages are working as they should. A 200 will mean that search engine crawlers can successfully crawl the page and it will be put into their search index.

What does 201 Created mean?

The 201 Created status code means that the request was successfully fulfilled and resulted in one or possibly multiple new resources being created.

What does 202 Accepted mean?

The 202 Accepted status code means that the request has been accepted for processing, but the processing has not been finished yet. The request may or may not be completed when the processing eventually takes place.

The 203 Non-Authoritative Information status code means that the request was successful. However, the meta-information that has been received is different from the one on the origin server and has instead been collected from a 3rd party or local copy. When not used for backups or mirrors of another resource a 200 OK response is preferable.

What does 204 No Content mean?

The 204 No Content status code means that while the server has successfully fulfilled the request, there is no available content for this request. But the user agent might want to update its currently cached headers for this resource, for the new one. 

What does 205 Reset Content mean?

The 205 Reset Content status code means that the user should reset the document that sent this request.

What does 206 Partial Content mean?

The 206 Partial Content response code is a response to a Range header sent from the client when requesting only a part of the resource.

What does 207 Multi-Status mean?

The 207 Multi-Status status code conveys information about multiple resources, in situation when multiple status codes are appropriate.

What does 208 Already Reported mean?

The 208 Already Reported status code is used inside the response element DAV: propstat, in order to avoid enumerating the internal members of multiple bindings to the same collection repeatedly.

What does 226 IM Used mean?

The 226 IM response code means that the server has successfully fulfilled a GET request for the resource, and the response is a representation of the result of one or multiple instance-manipulations applied to the current instance.

What does a 3xx Redirection code mean?

A 3xx Redirection status code means that you have been redirected and the completion of the request requires further action. Redirects are a natural part of the internet and you shouldn’t be scared to have 3xx redirect status codes on your website. A redirect means that the request was received successfully, but that the resource was found elsewhere. If a webpage has changed path and you try to access it through the old path, your CMS will often redirect the user to the new path. Ultimately the request will end in a 2xx success, but first it must go through the 3xx redirection.

  • 300 Multiple Choices
  • 301 Moved Permanently
  • 302 Found (Previously «Moved temporarily»)
  • 303 See Other
  • 304 Not Modified
  • 305 Use Proxy
  • 306 Switch Proxy
  • 307 Temporary Redirect
  • 308 Permanent Redirect

What does 300 Multiple Choices mean?

The 300 Multiple Choices status code means that the request has multiple possible responses and the user/user agent should choose one.

What does 301 Moved Permanently mean?

The 301 Moved Permanently response code means that the target resource has been assigned a new permanent URL and any references to this resources in the future should use one of the URLs included in the response.

When looking at things SEO-wise the 301 Permanent Redirect should be used every time a URL is moved permanently. This redirect passes your current link equity from your content to the new URL. Links that result in a status code 301 does give slightly less link equity than 200. So if you have a lot of links going through a 301 Permanent Redirect it is advised to fix these, if possible.

What does 302 Found (Previously “Moved temporarily”) mean?

The 302 Found status code, previously known as “Moved temporarily”, means that the URI of the request has been changed temporarily, and since changes can be made to the URI in the future, the effective request URI should be used for future requests.

When looking at things SEO-wise the 302 Found should only be used when making temporary changes as it does not pass the link equity the same way as a 301. If the page is not going to come back you should always use 301.

What does 303 See Other mean?

The 303 See Other response code is sent by the server in order to direct the client to get the requested resource at another URI with a GET request.

What does 304 Not Modified mean?

The 304 Not Modified response code informs the client that the response has not been modified. This means that the client can continue to use the already present, cached version of the response.

What does 305 Use Proxy mean?

The 305 Use Proxy status code instructs a client that it should connect to a proxy and then repeat the same request there. This response code is deprecated due to security concerns.

What does 306 Switch Proxy mean?

The 306 Switch proxy status code is no longer in use. It was used to inform the client that the subsequent requests should use the specified proxy.

What does 307 Temporary Redirect mean?

The 307 Temporary Redirect status code gets sent by the server in order to direct the client to the requested resource at another URI. The request method, however, must not be changed.

What does 308 Permanent Redirect mean?

The 308 Permanent Redirect status code means that the requested resource has been permanently assigned a new URI and future references to the resource should be made by using one of the enclosed URIs.

What does a 4xx Client Error mean?

A 4xx Client Error status code means that the website or the page could not be reached and either the page is unavailable or the request contains bad syntax. As a website owner you should do your best to avoid these, as it means your users will not find what they’re looking for. This can be either pages that are no longer found and are either temporarily or permanently gone. Besides giving a bad user experience, it can also hurt your SEO efforts.

  • 400 Bad Request
  • 401 Unauthorized
  • 402 Payment Required
  • 403 Forbidden
  • 404 Not Found
  • 405 Method Not Allowed
  • 406 Not Acceptable
  • 407 Proxy Authentication Required
  • 408 Request Timeout
  • 409 Conflict
  • 410 Gone
  • 411 Length Required
  • 412 Precondition Failed
  • 413 Payload Too Large
  • 414 URI Too Long
  • 415 Unsupported Media Type
  • 416 Range Not Satisfiable
  • 417 Expectation Failed
  • 418 I’m a Teapot
  • 421 Misdirected Request
  • 422 Unprocessable Entity
  • 423 Locked
  • 424 Failed Dependency
  • 425 Too Early
  • 426 Upgrade Required
  • 428 Precondition Required
  • 429 Too Many Requests
  • 431 Request Header Fields Too Large
  • 451 Unavailable For Legal Reasons

What does 400 Bad Request mean?

The 400 Bad Request status code means that the server could not understand the request because of invalid syntax.

What does 401 Unauthorized mean?

The 401 Unauthorized status code means that the request has not been applied because the server requires user authentication.

What does 402 Payment Required mean?

The 402 Payment Required status code is a response reserved for future use. It was originally created to be implemented in digital payment systems, however, it is rarely used and a standard convention of using it does not exist.

What does 403 Forbidden mean?

The 403 Forbidden status code means that the client request has been rejected because the client does not have rights to access the content. Unlike a 401 error, the client’s identity is known to the server, but since they are not authorized to view the content, giving the proper response is rejected by the server.

What does error 404 mean?

The 404 Not Found status code means that the server either did not find a current representation for the requested resource or is trying to hide its existence from an unauthorized client.

When looking at things SEO-wise the 404 Not Found status code pages with a high volume of traffic should be redirected using a 301 to the most relevant page possible. For some pages, however, a 404 might be necessary, for example, if the product is out of stock for an extended period of time. If you have external links pointing to a page that returns 404, you will lose the link equity those links would otherwise give.

If you need to fix 404 errors, jump to this section.

What does 405 Method Not Allowed mean?

The 405 Method Not Allowed status code means that while the server knows the request method, the method has been disabled and can not be used.

What does 406 Not Acceptable mean?

The 406 Not Acceptable status code is sent by the server when it does not find any content following the criteria given by the user agent.

What does 407 Proxy Authentication Required mean?

The 407 Proxy Authentication Required status code means that the client must first be authenticated by a proxy (similar to a 401).

What does 408 Request Timeout mean?

The 408 Request Timeout status code means that the server did not receive a complete request in the time that it prepared to wait.

What does 409 Conflict mean?

The 409 Conflict status code means that the request could not be fulfilled due to a conflict with the current state of the target resource and is used in situations where the user might be able to resubmit the request after resolving the conflict.

What does 410 Gone mean?

The 410 Gone status code means that the target resource has been deleted and the condition seems to be permanent. 

When looking at things SEO-wise the 410 Gone status code is a more permanent version a 404. The page will no longer be available from the server and has no forwarding address available. If you want to completely remove a page from Googles search index, then using 410 on a page is the proper way of doing it (instead of simply 404). 

What does 411 Length Required mean?

The 411 Length Required status code means that the server has rejected the request because it requires the Content-Length header field to be defined.

What does 412 Precondition Failed mean?

The 412 Precondition Failed status code means the server does not meet one or multiple preconditions that were indicated in the request header fields.

What does 413 Payload Too Large mean?

The 413 Payload Too Large status code means the server refuses to process the request because the request payload is larger than the server is able or willing to process. While the server may close the connection to prevent the client from continuing the request, it should generate a Retry-After header field and after how long can the client retry.

What does 414 URI Too Long mean?

The 414 URI Too Long status code means that the server is refusing to service the request because the request-target was longer than the server was willing to interpret.

What does 415 Unsupported Media Type mean?

The 415 Unsupported Media Type status code means that the server is rejecting the request because it does not support the media format of the requested data.

What does 416 Range Not Satisfiable mean?

The 416 Range Not Satisfiable status code means that the range specified in the Range header field of the request can’t be fulfilled. The reason might be that the given range is outside the size of the target URI’s data.

What does 417 Expectation Failed mean?

The 417 Expectation Failed status code means that the Expectation indicated by the Expect request-header field could not be met by the server.

What does 418 I’m a Teapot mean?

The 418 I’m a Teapot status code means that the server refuses to brew coffee because it is, in fact, a teapot. (It is a reference to a 1998 April Fools’ joke called »Hyper Text Coffee Pot Control Protocol»).

What does 421 Misdirected Request mean?

The 421 Misdirected Request status code means that the client request was directed at a server that is not configured to produce a response.

What does 422 Unprocessable Entity mean?

The 422 Unprocessable Entity status code means that while the request was well-formed, the server was unable to follow it, due to semantic errors.

What does 423 Locked mean?

The 423 Locked status code means that the resource that is being accessed is locked.

What does 424 Failed Dependency mean?

The 424 Failed Dependency status code means that the request failed due to the failure of a previous request.

What does 425 Too Early mean?

The 425 Too Early status code means that the server is not willing to risk processing a request that might be replayed.

What does 426 Upgrade Required mean?

The 426 Upgrade Required status code means that while the server refuses to perform the given request using the current protocol, it might be willing to do so after the client has been upgraded to a different protocol.

What does 428 Precondition Required mean?

The 428 Precondition Required status code means that the origin server requires the request to be conditional.

What does 429 Too Many Requests mean?

The 429 Too Many Requests response code means that in the given time, the user has sent too many requests.

The 431 Request Header Fields Too Large means that the server is not willing to process the request because its header fields are indeed too large, however, the request may be submitted again once the size of the request header fields is reduced.

What does 451 Unavailable For Legal Reasons mean?

The 451 Unavailable For Legal Reasons response code means that the user has requested an illegal resource (such as pages and sites blocked by the government).

What does a 5xx Server error mean?

A 5xx Server error status code means that while the request appears to be valid, the server could not complete the request. If you’re experiencing 5xx server errors for your website, you should immediately look at your server. If you’re hosting your own server you’ll need to start debugging to figure out why it is not responding properly. If you’re using an external hosting provider you’ll need to reach out to them, so they can look at it.

  • 500 Internal Server Error
  • 501 Not Implemented
  • 502 Bad Gateway
  • 503 Service Unavailable
  • 504 Gateway Timeout
  • 505 HTTP Version Not Supported
  • 506 Variant Also Negotiates
  • 507 Insufficient Storage
  • 508 Loop Detected
  • 510 Not Extended
  • 511 Network Authentication Required

What does 500 Internal Server Error mean?

The 500 Internal Server Error status code means that the server has encountered a situation that it does not know how to handle.

When looking at things SEO-wise the 500 Internal Server Error indicates a problem with the server, not the actual availability of the content. Since bots and users will both be lost, the link equity will go down fast.

What does 501 Not Implemented mean?

The 501 Not Implemented response code means that the request can not be handled because it is not supported by the server.

What does 502 Bad Gateway mean?

The 502 Bad Gateway response code means that the server received an invalid response while working as a gateway to handle the response.

What does 503 Service Unavailable mean?

The 503 Service Unavailable response code means that the server is currently not ready to handle the request. This is a common occurrence when the server is down for maintenance or is overloaded.

When looking at things SEO-wise the 503 Service Unavailable status code means that the server is unavailable and the visitor, bot or human, is asked to return again at a later time. This could be because of either server maintenance or server overload and search engines know to come back and check the availability later.

If you want to fix 503 errors, jump to this section.

What does 504 Gateway Timeout mean?

The 504 Gateway Timeout response code means that the server acting as a gateway could not get a response time.

What does 505 HTTP Version Not Supported mean?

The 505 HTTP Version Not Supported response code means that the version of HTTP used in the request is not supported by the server.

What does 506 Variant Also Negotiates mean?

The 506 Variant Also Negotiates response code means that the server has the following internal configuration error: The chosen variant resource is configured to engage in transparent negotiation itself, therefore it cannot be a proper endpoint in the negotiation process.

What does 507 Insufficient Storage mean?

The 507 Insufficient Storage status code means that the method could not be performed on the resource because the server is not able to store the representation that would be needed to complete the request successfully.

What does 508 Loop Detected mean?

The 508 Loop Detected response code means that the server has detected an infinite loop while processing the request.

What does 510 Not Extended mean?

The 510 Not Extended response code means that further extensions are required for the server to be able to fulfil the request.

What does 511 Network Authentication Required mean?

The 511 Network Authentication Required response code indicates that the client needs to authenticate to gain network access. 

HTTP Status Codes & SEO: Here are the ones you need to know

If you want great results with your SEO it’s important to work with technical SEO. A big part of that is handling response codes on your website to ensure that the website is properly crawled by Googlebot and that your content returns the proper response code when it is requested.

Below are the 5 status codes that you need to know as an SEO.

Browser with Umbraco logo icon

200 OK & SEO

This is the goal for 99 % of your content (pages, media, etc.): a successful status code that means everything works like it should. This is critical to a well-functioning website and for a great user experience.

It also gives you the reassurance that all external pointing to your website will give you link value. If all of your content returns a 200 OK status code you can rest assured that your website is working and is properly accessible for crawlers and visitors alike.

301 Moved Permanently & SEO

In a perfect world all of your content will stay on the same URL and always respond with a 200 OK. But that’s rarely how it works in the real world when managing a website.

If a page has changed its URL you will need to set up a redirect to send users and bots from the old URL to the new URL. Otherwise they will be met by a 404 page (see explanation below). In some content management systems, automatic redirect is a built-in SEO feature, while in others you’ll have to manually set it up.

You should use 301 redirects if the page is permanently gone and will not come back. This is the case for pages that have changed their URL or content that has been deleted.

If something is gone, instead of simply moved, you can either let it become a 404 or choose to redirect it to something similar on your website. This could be a product that you’re no longer going to sell, where it can make sense to redirect that page to the category page instead.

302 Found & SEO

What if the page is only gone temporarily, but will come back again later? To give a good user experience you don’t want it to become a 404 page and you also don’t want to make a permanent 301 redirect.

The solution is to use 302 Found instead of a 301. To the user it will be the same, but to search engine crawlers and bots, it will tell them to check back later on, as this redirect is only temporary. That means the old URL will keep its value while it’s gone.

This is perfect for pages that will only be unavailable temporarily. An example could be a sold-out product which is removed from the website until it is back in stock. In that case you want to make use of a 302 Found temporary redirect. Once the product is back online, you remove the redirect and the page will have kept its value (and good rankings in search engines).

Note that if the 302 redirect is there for too long, Google will consider it a 301 permanent redirect instead.

404 Not Found & SEO

If a page is no longer found it will result in a 404 page (psst, here’s some tips on how to make a great 404 page). This means, that the server tells users, crawlers and bots that the page they were looking for is not found. 

These are important to keep an eye on, as they can hurt your SEO a lot if not monitored and fixed.

Firstly, if a page returns a 404 it won’t be shown in Google’s search results. While it won’t get removed instantly, it will be after a short period of time, if not fixed. So if any of the pages that give you organic traffic end up returning a 404 error, you need to fix it quickly. See some tips on how to fix 404 errors here.

Secondly, if the page had any external links pointing to it, they will no longer give any value to your website. So even if the page does not receive any organic traffic, it can hurt your SEO performance.

The easiest way to fix this problem is to set up a 301 redirect. This will give a better user experience and will pass most of the link value from external links to the new page you’re redirecting to.

410 Gone & SEO

What if you actually want a page to completely disappear from Google’s search engine index? It might be intuitive to simply let it return a 404 error, but there’s one caveat with that:

404 does not tell crawlers and bots why the page was not found. For that reason, Google still might keep thinking that the page is there, even if it encounters a 404 error. In most cases this is fine, but there’s one case where you want to make it crystal clear that the content is gone. And that’s if you have been hacked and malicious content has been added to your website.

After doing cleanup it’s not enough to let the URLs return 404. Instead you should make sure that they return the 410 Gone status code. This clearly tells crawlers and bots that the page is gone for good and that they should remove it from their index.

5xx Server errors & SEO

The last one is not directly SEO-related, but more of a good tip for troubleshooting your website.

If you see any response code that start with 5xx, you should instantly know that it is a server error. This will help you greatly when it comes to troubleshooting and fixing it. 

Instead of wasting time trying to fix the problem through your CMS backend or elsewhere, you can go straight to fixing the server. No matter if you do your own hosting or if you use a hosting provider, it is helpful to know that it’s related to the server, not your website.

How to check the HTTP status code of a page

Finding the server response code for a page can be done manually in your browser or by using various tools and website crawlers.

Depending on the browser you’re using it is slightly different. Below is how to do it in Chrome (most steps will be similar in other browsers).

Checking HTTP status code in Chrome

  1. Open the URL your want to check with your browser
  2. Open the Developer tab (F12) and go to the «Network» tab
  3. Refresh the page
  4. Scroll to the top of the list of requests and find the first of type «document»
  5. In «Status» you can now find the HTTP response code

Find HTTP status code in Chrome

How to fix 404 errors

If you have seen the status code 404 Page Not found you might have been thinking «What does error 404 mean?»

HTTP status code 404 means «Page Not Found». This means that the request you sent was received by the server, but it could not find the page you were looking for.

So to fix the 404 error you first need to find the cause for it, which can be due to many things. But since you know that the server is reachable (otherwise it would have returned a 5xx error), you know that the error is client-side. Basically that means it’s your fault (not as harsh as it sounds).

Luckily it means that you can also fix the error on your end without having to debugging your server or reaching out to your hosting provider.

Fix 404 errors

Run through this checklist to fix the 404 error:

  1. Refresh the page. It might seem simple, but a 404 error could have just been a temporary issue that is fixed simply by trying again.
  2. Check the URL you typed in. Did you make a mistake somewhere? If the URL you typed is not exactly right a 404 is to be expected (unless a 3xx redirect is set up)
  3. If no mistake was made, try again from a different device like your mobile phone or tablet. If it works from a different device it’s most likely due to browser cache and cookies. Clear the browser cache and delete cookies, then try to access the page again.

If none of the above tricks worked, it’s likely that the piece of content was deleted or some other way moved. If the content was moved, which caused it to change URL, then you should make sure to set up a redirect that points from the old URL to the new one. That way you’re sure that anyone looking for the page can still find it.

If it was deleted, then a 404 error is the right response as the page truly was not found on your website and everything is working as it should.

If you see a lot of your visitors ending up on this page, then it’s most likely due to one of 3 things:

  1. You have an internal link on your website pointing to the page. If that’s the case, you should remove (or change) this link so it no longer points to a page that is not found.
  2. External websites link to the page. This is trickier as you can’t simply change it (although you can reach out to the websites and ask them to change it). A more simple thing for you to do would be to add a 301 redirect and point from the page to a different page on your website. That way you lead people to a page that is working, while also being a SEO-friendly option.
  3. The page is still showing up in Google’s search results and sending traffic to your website. While this is usually short-lived, it is possible that a 404 page can stay in the search results for a while, as a 404 does not tell Googlebot whether the page is temporarily or permanently missing. If this is happening, you’ll need to get the page back quickly or redirect it to a different page, so you won’t lose your rankings in Google.

Find 404 pages in Google Analytics

Have you ever wondered if there’s a way to find 404 pages in Google Analytics?

Well, the good news is, there are ways to find them within your analytics setup. Now this can sometimes come down to how your website is configured. One way to find them is to check by page title — Your 404 page will very likely have “404” or “Page not found” in the title. It’s very easy to find the 404 page this way:

  • Within your analytics tool, go to behavior → Site Content → All Pages.
  • Now you can set your primary dimension to Page title and search for  “404” or “Page not Found”.
  • And now — you should hopefully have your 404 report.

Now this is not the only way to set it up, but there is a very good chance that you can find the pages this way. 

Fix 503 errors

How to fix 503 errors

The 503 response code means «Service Unavailable» and happens when a server is currently not ready to handle the request. This can be either due to the server being down for maintenance or if it is overloaded.

If this error occurs on your own website, you need to have a look at your server, as something is making it unable to process the requests made.

Unfortunately it’s not always easy and simple to fix. A 503 response code can be due to many things, but at least you know it’s server-related and not client-side like with a 404 error.

Here’s a list of steps you can go through to identify and fix a 503 error:

  1. Is your website still running and receiving traffic? Check your Analytics tools or server logs to see if other visitors are getting through to your website.
  2. If it’s no longer receiving traffic your server might be under maintenance or have crashed. If it’s under maintenance then a 503 is to be expected and everything will work fine once it’s done. If it crashed you should try restarting it.
  3. If you’re receiving huge amounts of website traffic, the server is most likely overloaded and returning 503 errors because it doesn’t have the resources to keep up. Before fixing such an issue you need to identify it the traffic is from real visitors or if you’re the victim of a DoS or DDoS attack.
  4. Identifying a DoS or DDoS attack can be hard, but the most effective ways are:
    1. Checking if one or more IP addresses make a lot of requests
    2. The TTL (time to live) on a ping request times out
    3. Analyzing the server logs and seeing huge spikes in traffic
  5. If it looks to be a DoS or DDoS attack, you’ll need to apply one or more defense techniques to stop the attack. 
  6. If it is not a DoS or DDoS attack, then your website has most likely become more popular than your server can handle. The best way to fix such an issue is to look at connection limits, bandwidth throttling, system resources, fail-safes that might have triggered or anything that might be limiting server performance. Essentially you’ll need to upgrade your server so it has the proper resources to handle the traffic.

The above list is great for troubleshooting one-off 503 errors. But if it happens on a regular basis, then it might be a more permanent problem with your server that you should dive deeper into fixing. This can be inefficient processes using up all of your resources or your server simply not having enough allocated resources to handle the traffic your website is receiving.

What status code is returned by a website when the browser request is successful?

With all these HTTP status codes — It can be a bit daunting to figure if any of them are good. But some of them are.
A browser will return a 2xx status code if the browser request was successful. So a 2xx code is the one you want to see. The 200 status code means that the browser’s request was successful and received, understood, and accepted.

Источник

REST APIs use the Status-Line part of an HTTP response message to inform clients of their request’s overarching result. RFC 2616 defines the Status-Line syntax as shown below:

Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF

HTTP defines these standard status codes that can be used to convey the results of a client’s request. The status codes are divided into five categories.

  • 1xx: Informational – Communicates transfer protocol-level information.
  • 2xx: Success – Indicates that the client’s request was accepted successfully.
  • 3xx: Redirection – Indicates that the client must take some additional action in order to complete their request.
  • 4xx: Client Error – This category of error status codes points the finger at clients.
  • 5xx: Server Error – The server takes responsibility for these error status codes.

1xx Status Codes [Informational]

Status Code

Description

100 Continue

An interim response. Indicates to the client that the initial part of the request has been received and has not yet been rejected by the server. The client SHOULD continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The server MUST send a final response after the request has been completed.

101 Switching Protocol

Sent in response to an Upgrade request header from the client, and indicates the protocol the server is switching to.

102 Processing (WebDAV)

Indicates that the server has received and is processing the request, but no response is available yet.

103 Early Hints

Primarily intended to be used with the Link header. It suggests the user agent start preloading the resources while the server prepares a final response.

2xx Status Codes [Success]

Status Code

Description

200 OK

Indicates that the request has succeeded.

201 Created

Indicates that the request has succeeded and a new resource has been created as a result.

202 Accepted

Indicates that the request has been received but not completed yet. It is typically used in log running requests and batch processing.

203 Non-Authoritative Information

Indicates that the returned metainformation in the entity-header is not the definitive set as available from the origin server, but is gathered from a local or a third-party copy. The set presented MAY be a subset or superset of the original version.

204 No Content

The server has fulfilled the request but does not need to return a response body. The server may return the updated meta information.

205 Reset Content

Indicates the client to reset the document which sent this request.

206 Partial Content

It is used when the Range header is sent from the client to request only part of a resource.

207 Multi-Status (WebDAV)

An indicator to a client that multiple operations happened, and that the status for each operation can be found in the body of the response.

208 Already Reported (WebDAV)

Allows a client to tell the server that the same resource (with the same binding) was mentioned earlier. It never appears as a true HTTP response code in the status line, and only appears in bodies.

226 IM Used

The server has fulfilled a GET request for the resource, and the response is a representation of the result of one or more instance-manipulations applied to the current instance.

3xx Status Codes [Redirection]

Status Code

Description

300 Multiple Choices

The request has more than one possible response. The user-agent or user should choose one of them.

301 Moved Permanently

The URL of the requested resource has been changed permanently. The new URL is given by the Location header field in the response. This response is cacheable unless indicated otherwise.

302 Found

The URL of the requested resource has been changed temporarily. The new URL is given by the Location field in the response. This response is only cacheable if indicated by a Cache-Control or Expires header field.

303 See Other

The response can be found under a different URI and SHOULD be retrieved using a GET method on that resource.

304 Not Modified

Indicates the client that the response has not been modified, so the client can continue to use the same cached version of the response.

305 Use Proxy (Deprecated)

Indicates that a requested response must be accessed by a proxy.

306 (Unused)

It is a reserved status code and is not used anymore.

307 Temporary Redirect

Indicates the client to get the requested resource at another URI with same method that was used in the prior request. It is similar to 302 Found with one exception that the same HTTP method will be used that was used in the prior request.

308 Permanent Redirect (experimental)

Indicates that the resource is now permanently located at another URI, specified by the Location header. It is similar to 301 Moved Permanently with one exception that the same HTTP method will be used that was used in the prior request.

4xx Status Codes (Client Error)

Status Code

Description

400 Bad Request

The request could not be understood by the server due to incorrect syntax. The client SHOULD NOT repeat the request without modifications.

401 Unauthorized

Indicates that the request requires user authentication information. The client MAY repeat the request with a suitable Authorization header field

402 Payment Required (Experimental)

Reserved for future use. It is aimed for using in the digital payment systems.

403 Forbidden

Unauthorized request. The client does not have access rights to the content. Unlike 401, the client’s identity is known to the server.

404 Not Found

The server can not find the requested resource.

405 Method Not Allowed

The request HTTP method is known by the server but has been disabled and cannot be used for that resource.

406 Not Acceptable

The server doesn’t find any content that conforms to the criteria given by the user agent in the Accept header sent in the request.

407 Proxy Authentication Required

Indicates that the client must first authenticate itself with the proxy.

408 Request Timeout

Indicates that the server did not receive a complete request from the client within the server’s allotted timeout period.

409 Conflict

The request could not be completed due to a conflict with the current state of the resource.

410 Gone

The requested resource is no longer available at the server.

411 Length Required

The server refuses to accept the request without a defined Content- Length. The client MAY repeat the request if it adds a valid Content-Length header field.

412 Precondition Failed

The client has indicated preconditions in its headers which the server does not meet.

413 Request Entity Too Large

Request entity is larger than limits defined by server.

414 Request-URI Too Long

The URI requested by the client is longer than the server can interpret.

415 Unsupported Media Type

The media-type in Content-type of the request is not supported by the server.

416 Requested Range Not Satisfiable

The range specified by the Range header field in the request can’t be fulfilled.

417 Expectation Failed

The expectation indicated by the Expect request header field can’t be met by the server.

418 I’m a teapot (RFC 2324)

It was defined as April’s lool joke and is not expected to be implemented by actual HTTP servers. (RFC 2324)

420 Enhance Your Calm (Twitter)

Returned by the Twitter Search and Trends API when the client is being rate limited.

422 Unprocessable Entity (WebDAV)

The server understands the content type and syntax of the request entity, but still server is unable to process the request for some reason.

423 Locked (WebDAV)

The resource that is being accessed is locked.

424 Failed Dependency (WebDAV)

The request failed due to failure of a previous request.

425 Too Early (WebDAV)

Indicates that the server is unwilling to risk processing a request that might be replayed.

426 Upgrade Required

The server refuses to perform the request. The server will process the request after the client upgrades to a different protocol.

428 Precondition Required

The origin server requires the request to be conditional.

429 Too Many Requests

The user has sent too many requests in a given amount of time (“rate limiting”).

431 Request Header Fields Too Large

The server is unwilling to process the request because its header fields are too large.

444 No Response (Nginx)

The Nginx server returns no information to the client and closes the connection.

449 Retry With (Microsoft)

The request should be retried after performing the appropriate action.

450 Blocked by Windows Parental Controls (Microsoft)

Windows Parental Controls are turned on and are blocking access to the given webpage.

451 Unavailable For Legal Reasons

The user-agent requested a resource that cannot legally be provided.

499 Client Closed Request (Nginx)

The connection is closed by the client while HTTP server is processing its request, making the server unable to send the HTTP header back.

5xx Status Codes (Server Error)

Status Code

Description

500 Internal Server Error

The server encountered an unexpected condition that prevented it from fulfilling the request.

501 Not Implemented

The HTTP method is not supported by the server and cannot be handled.

502 Bad Gateway

The server got an invalid response while working as a gateway to get the response needed to handle the request.

503 Service Unavailable

The server is not ready to handle the request.

504 Gateway Timeout

The server is acting as a gateway and cannot get a response in time for a request.

505 HTTP Version Not Supported (Experimental)

The HTTP version used in the request is not supported by the server.

506 Variant Also Negotiates (Experimental)

Indicates that the server has an internal configuration error: the chosen variant resource is configured to engage in transparent content negotiation itself, and is therefore not a proper endpoint in the negotiation process.

507 Insufficient Storage (WebDAV)

The method could not be performed on the resource because the server is unable to store the representation needed to successfully complete the request.

508 Loop Detected (WebDAV)

The server detected an infinite loop while processing the request.

510 Not Extended

Further extensions to the request are required for the server to fulfill it.

511 Network Authentication Required

Indicates that the client needs to authenticate to gain network access.

6. REST Specific HTTP Status Codes

200 (OK)

It indicates that the REST API successfully carried out whatever action the client requested and that no more specific code in the 2xx series is appropriate.

Unlike the 204 status code, a 200 response should include a response body. The information returned with the response is dependent on the method used in the request, for example:

  • GET an entity corresponding to the requested resource is sent in the response;
  • HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
  • POST an entity describing or containing the result of the action;
  • TRACE an entity containing the request message as received by the end server.

201 (Created)

A REST API responds with the 201 status code whenever a resource is created inside a collection. There may also be times when a new resource is created as a result of some controller action, in which case 201 would also be an appropriate response.

The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header field.

The origin server MUST create the resource before returning the 201 status code. If the action cannot be carried out immediately, the server SHOULD respond with a 202 (Accepted) response instead.

202 (Accepted)

A 202 response is typically used for actions that take a long while to process. It indicates that the request has been accepted for processing, but the processing has not been completed. The request might or might not be eventually acted upon, or even maybe disallowed when processing occurs.

Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent’s connection to the server persist until the process is completed.

The entity returned with this response SHOULD include an indication of the request’s current status and either a pointer to a status monitor (job queue location) or some estimate of when the user can expect the request to be fulfilled.

204 (No Content)

The 204 status code is usually sent out in response to a PUT, POST, or DELETE request when the REST API declines to send back any status message or representation in the response message’s body.

An API may also send 204 in conjunction with a GET request to indicate that the requested resource exists, but has no state representation to include in the body.

If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This response is primarily intended to allow input for actions to take place without causing a change to the user agent’s active document view. However, any new or updated metainformation SHOULD be applied to the document currently in the user agent’s dynamic view.

The 204 response MUST NOT include a message-body and thus is always terminated by the first empty line after the header fields.

301 (Moved Permanently)

The 301 status code indicates that the REST API’s resource model has been significantly redesigned, and a new permanent URI has been assigned to the client’s requested resource. The REST API should specify the new URI in the response’s Location header, and all future requests should be directed to the given URI.

You will hardly use this response code in your API as you can always use the API versioning for the new API while retaining the old one.

302 (Found)

The HTTP response status code 302 Found is a common way of performing URL redirection. An HTTP response with this status code will additionally provide a URL in the Location header field. The user agent (e.g., a web browser) is invited by a response with this code to make a second. Otherwise identical, request to the new URL specified in the location field.

Many web browsers implemented this code in a manner that violated this standard, changing the request type of the new request to GET, regardless of the type employed in the original request (e.g., POST). RFC 1945 and RFC 2068 specify that the client is not allowed to change the method on the redirected request. The status codes 303 and 307 have been added for servers that wish to make unambiguously clear which kind of reaction is expected of the client.

303 (See Other)

A 303 response indicates that a controller resource has finished its work, but instead of sending a potentially unwanted response body, it sends the client the URI of a response resource. The response can be the URI of the temporary status message, or the URI to some already existing, more permanent, resource.

Generally speaking, the 303 status code allows a REST API to send a reference to a resource without forcing the client to download its state. Instead, the client may send a GET request to the value of the Location header.

The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable.

304 (Not Modified)

This status code is similar to 204 (“No Content”) in that the response body must be empty. The critical distinction is that 204 is used when there is nothing to send in the body, whereas 304 is used when the resource has not been modified since the version specified by the request headers If-Modified-Since or If-None-Match.

In such a case, there is no need to retransmit the resource since the client still has a previously-downloaded copy.

Using this saves bandwidth and reprocessing on both the server and client, as only the header data must be sent and received in comparison to the entirety of the page being re-processed by the server, then sent again using more bandwidth of the server and client.

307 (Temporary Redirect)

A 307 response indicates that the REST API is not going to process the client’s request. Instead, the client should resubmit the request to the URI specified by the response message’s Location header. However, future requests should still use the original URI.

A REST API can use this status code to assign a temporary URI to the client’s requested resource. For example, a 307 response can be used to shift a client request over to another host.

The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s). If the 307 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.

400 (Bad Request)

400 is the generic client-side error status, used when no other 4xx error code is appropriate. Errors can be like malformed request syntax, invalid request message parameters, or deceptive request routing etc.

The client SHOULD NOT repeat the request without modifications.

401 (Unauthorized)

A 401 error response indicates that the client tried to operate on a protected resource without providing the proper authorization. It may have provided the wrong credentials or none at all. The response must include a WWW-Authenticate header field containing a challenge applicable to the requested resource.

The client MAY repeat the request with a suitable Authorization header field. If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information.

403 (Forbidden)

A 403 error response indicates that the client’s request is formed correctly, but the REST API refuses to honor it, i.e., the user does not have the necessary permissions for the resource. A 403 response is not a case of insufficient client credentials; that would be 401 (“Unauthorized”).

Authentication will not help, and the request SHOULD NOT be repeated. Unlike a 401 Unauthorized response, authenticating will make no difference.

404 (Not Found)

The 404 error status code indicates that the REST API can’t map the client’s URI to a resource but may be available in the future. Subsequent requests by the client are permissible.

No indication is given of whether the condition is temporary or permanent. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.

405 (Method Not Allowed)

The API responds with a 405 error to indicate that the client tried to use an HTTP method that the resource does not allow. For instance, a read-only resource could support only GET and HEAD, while a controller resource might allow GET and POST, but not PUT or DELETE.

A 405 response must include the Allow header, which lists the HTTP methods that the resource supports. For example:

Allow: GET, POST

406 (Not Acceptable)

The 406 error response indicates that the API is not able to generate any of the client’s preferred media types, as indicated by the Accept request header. For example, a client request for data formatted as application/xml will receive a 406 response if the API is only willing to format data as application/json.

If the response could be unacceptable, a user agent SHOULD temporarily stop receipt of more data and query the user for a decision on further actions.

412 (Precondition Failed)

The 412 error response indicates that the client specified one or more preconditions in its request headers, effectively telling the REST API to carry out its request only if certain conditions were met. A 412 response indicates that those conditions were not met, so instead of carrying out the request, the API sends this status code.

415 (Unsupported Media Type)

The 415 error response indicates that the API is not able to process the client’s supplied media type, as indicated by the Content-Type request header. For example, a client request including data formatted as application/xml will receive a 415 response if the API is only willing to process data formatted as application/json.

For example, the client uploads an image as image/svg+xml, but the server requires that images use a different format.

500 (Internal Server Error)

500 is the generic REST API error response. Most web frameworks automatically respond with this response status code whenever they execute some request handler code that raises an exception.

A 500 error is never the client’s fault, and therefore, it is reasonable for the client to retry the same request that triggered this response and hope to get a different response.

The API response is the generic error message, given when an unexpected condition was encountered and no more specific message is suitable.

501 (Not Implemented)

The server either does not recognize the request method, or it cannot fulfill the request. Usually, this implies future availability (e.g., a new feature of a web-service API).

References :

https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml

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