HTTP Status Code Flashcards: Meanings, Classes & Use Cases

Learn registered HTTP response status codes by number, reason phrase, class, and practical use case, with current IANA and RFC references.

Об этой колоде

Learn the current IANA-registered HTTP response status codes as a practical recall system, not a loose cheat sheet.

What this deck practices

  • Code → meaning: all 61 response codes assigned in the IANA registry snapshot used on 25 August 2026, starting with the registered reason phrase and a concise RFC-based explanation.
  • Meaning → code: 27 selective reverse cards for common, atomic retrieval targets. These are not mechanical reversals of every entry.
  • Class purpose: exactly five cards for 1xx Informational, 2xx Successful, 3xx Redirection, 4xx Client Error, and 5xx Server Error.
  • Confusion sets: 401 vs 403; 301/302/307/308; 409 vs 422; 404 vs 410; 202 vs 204; and 502 vs 504.

The order introduces the five classes and common responses first, broadens through the registered set, and finishes with comparison and reference material. Forward and reverse variants are separated so one card does not immediately reveal another.

Special registry status

Temporary 104 Upload Resumption Supported is clearly marked with IANA’s recorded expiry of 13 November 2026. HTTP 402 is taught as registered but reserved by RFC 9110 for future use. Unused 306 and 418, plus obsoleted 510, live in a separate reference section rather than the ordinary recall sequence. Unassigned codes and ranges are excluded because they have no registered reason phrase or stable meaning to recall. Deprecated 305 is labeled accurately.

Explanations follow the IANA HTTP Status Code Registry and its linked RFC references. Reason phrases are labels, not complete normative semantics. Examples and comparisons are original paraphrases and do not prescribe one universal REST API design.

This is an independent, unofficial educational deck by Flashcards Open Source App. It is not affiliated with, endorsed by, or produced by IANA, the IETF, or the RFC Editor. No competitor deck, RFC prose, copyrighted table, or exam question was copied. The CC0 label applies to the original prompts, explanations, organization, metadata, and generated cover to the extent applicable rights exist; it does not claim ownership of facts or standards text.

Карточки в этой колоде

  1. Карточка 1

    Вопрос

    What is the purpose of the 1xx HTTP status-code class?

    Ответ

    Informational. A 1xx response is interim: it communicates connection status or request progress before the final response.

  2. Карточка 2

    Вопрос

    What is the purpose of the 2xx HTTP status-code class?

    Ответ

    Successful. A 2xx response means the request was successfully received, understood, and accepted.

  3. Карточка 3

    Вопрос

    What is the purpose of the 3xx HTTP status-code class?

    Ответ

    Redirection. A 3xx response means the user agent needs to take further action to fulfill the request, such as following another URI or using a cached representation.

  4. Карточка 4

    Вопрос

    What is the purpose of the 4xx HTTP status-code class?

    Ответ

    Client Error. A 4xx response means the client appears to have made an error; it does not prove that every fault lies in client code.

  5. Карточка 5

    Вопрос

    What is the purpose of the 5xx HTTP status-code class?

    Ответ

    Server Error. A 5xx response means the server knows it has erred or cannot perform the requested method.

  6. Карточка 6

    Вопрос

    What does HTTP status code 200 mean?

    Ответ

    OK. The request succeeded; the meaning of any response content depends on the request method.

  7. Карточка 7

    Вопрос

    What does HTTP status code 404 mean?

    Ответ

    Not Found. The origin server has no current representation for the target resource, or it is unwilling to disclose that one exists. The code does not say whether the condition is temporary or permanent.

  8. Карточка 8

    Вопрос

    What does HTTP status code 301 mean?

    Ответ

    Moved Permanently. The target resource has a new permanent URI. For historical reasons, a user agent may change POST to GET when following it; use 308 when method preservation matters.

  9. Карточка 9

    Вопрос

    What does HTTP status code 500 mean?

    Ответ

    Internal Server Error. The server hit an unexpected condition that prevented it from fulfilling the request.

  10. Карточка 10

    Вопрос

    What does HTTP status code 201 mean?

    Ответ

    Created. The request was fulfilled and created one or more resources. The primary resource is identified by Location, or by the target URI when Location is absent.

  11. Карточка 11

    Вопрос

    What does HTTP status code 401 mean?

    Ответ

    Unauthorized. The request was not applied because it lacks valid authentication credentials for the target resource. The response includes a WWW-Authenticate challenge.

  12. Карточка 12

    Вопрос

    What does HTTP status code 503 mean?

    Ответ

    Service Unavailable. The server is temporarily unable to handle the request, often because of overload or maintenance. It may send Retry-After.

  13. Карточка 13

    Вопрос

    What does HTTP status code 204 mean?

    Ответ

    No Content. The server successfully fulfilled the request and has no additional response content to send.

  14. Карточка 14

    Вопрос

    What does HTTP status code 403 mean?

    Ответ

    Forbidden. The server understood the request but refuses to fulfill it. Credentials may be insufficient, or the refusal may be unrelated to authentication.

  15. Карточка 15

    Вопрос

    What does HTTP status code 302 mean?

    Ответ

    Found. The target resource is temporarily available at another URI, so future requests should still use the original URI. A user agent may change POST to GET when following it.

  16. Карточка 16

    Вопрос

    What does HTTP status code 400 mean?

    Ответ

    Bad Request. The server cannot or will not process the request because of a perceived client error, such as malformed syntax, invalid framing, or deceptive routing.

  17. Карточка 17

    Вопрос

    What does HTTP status code 502 mean?

    Ответ

    Bad Gateway. A server acting as a gateway or proxy received an invalid response from an inbound server while trying to fulfill the request.

  18. Карточка 18

    Вопрос

    Which HTTP status code has the registered reason phrase “OK”?

    Ответ

    200 OK. It indicates that the request succeeded.

  19. Карточка 19

    Вопрос

    What does HTTP status code 202 mean?

    Ответ

    Accepted. The request was accepted for processing, but processing is incomplete and might not ultimately happen.

  20. Карточка 20

    Вопрос

    Which HTTP status code has the registered reason phrase “Not Found”?

    Ответ

    404 Not Found. It means there is no current representation for the target resource, or the server will not disclose one.

  21. Карточка 21

    Вопрос

    What does HTTP status code 304 mean?

    Ответ

    Not Modified. A conditional GET or HEAD would otherwise have returned 200, but the condition was false, so the client can use its stored representation. A 304 response has no content.

  22. Карточка 22

    Вопрос

    Which HTTP status code has the registered reason phrase “Created”?

    Ответ

    201 Created. It means the fulfilled request created one or more resources.

  23. Карточка 23

    Вопрос

    Which HTTP status code means the request lacks valid authentication credentials?

    Ответ

    401 Unauthorized. The response challenges the client to authenticate for the target resource.

  24. Карточка 24

    Вопрос

    Which HTTP status code has the registered reason phrase “Internal Server Error”?

    Ответ

    500 Internal Server Error. It covers an unexpected server condition that prevented fulfillment.

  25. Карточка 25

    Вопрос

    Which HTTP status code means success with no additional response content?

    Ответ

    204 No Content. The action succeeded, and there is no response content to send.

  26. Карточка 26

    Вопрос

    Which HTTP status code means the server understood the request but refuses to fulfill it?

    Ответ

    403 Forbidden. Repeating the same request with the same credentials should not be automatic.

  27. Карточка 27

    Вопрос

    Which HTTP status code has the registered reason phrase “Moved Permanently”?

    Ответ

    301 Moved Permanently. Future references should use the new permanent URI.

  28. Карточка 28

    Вопрос

    Which HTTP status code means the server is temporarily unable to handle the request?

    Ответ

    503 Service Unavailable. Temporary overload or maintenance are typical reasons.

  29. Карточка 29

    Вопрос

    Which HTTP status code has the registered reason phrase “Bad Request”?

    Ответ

    400 Bad Request. The server perceives a client-side problem that prevents or discourages processing.

  30. Карточка 30

    Вопрос

    Which HTTP status code means a gateway or proxy received an invalid inbound response?

    Ответ

    502 Bad Gateway. The upstream response arrived, but it was invalid.

  31. Карточка 31

    Вопрос

    Which HTTP status code has the registered reason phrase “Accepted”?

    Ответ

    202 Accepted. Processing has been accepted but is not complete.

  32. Карточка 32

    Вопрос

    Which HTTP status code tells a conditional GET or HEAD to use a stored representation?

    Ответ

    304 Not Modified. The request condition evaluated false, so the stored representation remains valid for this response.

  33. Карточка 33

    Вопрос

    What does HTTP status code 100 mean?

    Ответ

    Continue. The server received the initial part of the request and has not rejected it. With Expect: 100-continue, the client should continue sending the request content.

  34. Карточка 34

    Вопрос

    What does HTTP status code 206 mean?

    Ответ

    Partial Content. The server is successfully fulfilling a range request by transferring one or more parts of the selected representation.

  35. Карточка 35

    Вопрос

    What does HTTP status code 307 mean?

    Ответ

    Temporary Redirect. The resource is temporarily at another URI, and an automatic redirect must preserve the request method.

  36. Карточка 36

    Вопрос

    What does HTTP status code 409 mean?

    Ответ

    Conflict. The request cannot be completed because it conflicts with the target resource’s current state. The client may be able to resolve the conflict and resubmit.

  37. Карточка 37

    Вопрос

    What does HTTP status code 504 mean?

    Ответ

    Gateway Timeout. A gateway or proxy did not receive a timely response from an upstream server needed to complete the request.

  38. Карточка 38

    Вопрос

    What does HTTP status code 101 mean?

    Ответ

    Switching Protocols. The server accepts the client’s Upgrade request and names the protocol that will be used after this response.

  39. Карточка 39

    Вопрос

    Which HTTP status code means a range request succeeded with only part of the representation?

    Ответ

    206 Partial Content. The response carries one or more requested ranges.

  40. Карточка 40

    Вопрос

    Which temporary redirect status code requires method preservation?

    Ответ

    307 Temporary Redirect. An automatic redirect must not change the request method.

  41. Карточка 41

    Вопрос

    Which HTTP status code means a request conflicts with the target resource’s current state?

    Ответ

    409 Conflict. The client may be able to resolve the state conflict and try again.

  42. Карточка 42

    Вопрос

    Which HTTP status code means a gateway timed out waiting for an upstream server?

    Ответ

    504 Gateway Timeout. The upstream response did not arrive in time.

  43. Карточка 43

    Вопрос

    What does HTTP status code 102 mean?

    Ответ

    Processing. This registered interim response says the server accepted the complete request but has not finished processing it; a final response still follows.

  44. Карточка 44

    Вопрос

    What does HTTP status code 203 mean?

    Ответ

    Non-Authoritative Information. The request succeeded, but a transforming proxy modified the enclosed content from the origin server’s 200 response.

  45. Карточка 45

    Вопрос

    What does HTTP status code 308 mean?

    Ответ

    Permanent Redirect. The resource has a new permanent URI, and an automatic redirect must preserve the request method.

  46. Карточка 46

    Вопрос

    What does HTTP status code 410 mean?

    Ответ

    Gone. Access to the target resource is no longer available at the origin server, and the condition is likely permanent.

  47. Карточка 47

    Вопрос

    What does HTTP status code 501 mean?

    Ответ

    Not Implemented. The server does not support functionality required to fulfill the request, such as an unrecognized method it cannot support for any resource.

  48. Карточка 48

    Вопрос

    What does HTTP status code 103 mean?

    Ответ

    Early Hints. This interim response carries header fields the server is likely to include in the final response, letting the client make safe performance optimizations while it waits.

  49. Карточка 49

    Вопрос

    What does HTTP status code 205 mean?

    Ответ

    Reset Content. The request succeeded, and the server wants the user agent to reset the document view that caused the request. The response has no content.

  50. Карточка 50

    Вопрос

    Which permanent redirect status code requires method preservation?

    Ответ

    308 Permanent Redirect. Future requests should use the new URI without changing the method during automatic redirection.

  51. Карточка 51

    Вопрос

    Which HTTP status code says a resource is no longer available and is likely gone permanently?

    Ответ

    410 Gone. Use 404 when the server does not know whether the absence is permanent.

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    HTTP Status Code Flashcards: Meanings, Classes & Use Cases

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  52. Карточка 52

    Вопрос

    Which HTTP status code means the required server functionality is unsupported?

    Ответ

    501 Not Implemented. It applies when the server cannot support the functionality needed to fulfill the request.

  53. Карточка 53

    Вопрос

    What does HTTP status code 207 mean?

    Ответ

    Multi-Status. The response reports status for multiple independent operations, as defined for WebDAV.

  54. Карточка 54

    Вопрос

    What does HTTP status code 300 mean?

    Ответ

    Multiple Choices. The target has more than one representation, and the response provides alternatives so the user or user agent can choose.

  55. Карточка 55

    Вопрос

    What does HTTP status code 405 mean?

    Ответ

    Method Not Allowed. The origin server knows the request method, but the target resource does not support it. The response includes an Allow field.

  56. Карточка 56

    Вопрос

    What does HTTP status code 505 mean?

    Ответ

    HTTP Version Not Supported. The server does not support, or refuses to support, the major HTTP version used in the request.

  57. Карточка 57

    Вопрос

    What does HTTP status code 208 mean?

    Ответ

    Already Reported. Inside a WebDAV multistatus response, it avoids repeatedly enumerating descendants of another binding to the same collection.

  58. Карточка 58

    Вопрос

    What does HTTP status code 303 mean?

    Ответ

    See Other. The Location URI identifies a different resource that can provide an indirect response; the user agent retrieves it with GET or HEAD.

  59. Карточка 59

    Вопрос

    What does HTTP status code 406 mean?

    Ответ

    Not Acceptable. The target has no current representation acceptable under the request’s proactive negotiation fields, and the server will not send a default.

  60. Карточка 60

    Вопрос

    What does HTTP status code 506 mean?

    Ответ

    Variant Also Negotiates. The server has a transparent content-negotiation configuration error: the chosen variant is itself configured to negotiate.

  61. Карточка 61

    Вопрос

    What does HTTP status code 226 mean?

    Ответ

    IM Used. The server fulfilled a GET by returning the result of one or more instance manipulations applied to the current representation, identified in the IM response field.

  62. Карточка 62

    Вопрос

    What does HTTP status code 305 mean?

    Ответ

    Use Proxy — deprecated. It was defined to direct access through a proxy, but RFC 9110 marks the status code deprecated. New implementations should not rely on it.

  63. Карточка 63

    Вопрос

    What does HTTP status code 407 mean?

    Ответ

    Proxy Authentication Required. The client must authenticate to a proxy for this request. The proxy sends a Proxy-Authenticate challenge.

  64. Карточка 64

    Вопрос

    What does HTTP status code 507 mean?

    Ответ

    Insufficient Storage. The server cannot store the representation needed to complete the method. WebDAV defines this as a temporary condition.

  65. Карточка 65

    Вопрос

    What does HTTP status code 408 mean?

    Ответ

    Request Timeout. The server did not receive a complete request message within the time it was prepared to wait.

  66. Карточка 66

    Вопрос

    What does HTTP status code 508 mean?

    Ответ

    Loop Detected. The server terminated a WebDAV operation after finding an infinite loop while processing a Depth: infinity request.

  67. Карточка 67

    Вопрос

    What does HTTP status code 412 mean?

    Ответ

    Precondition Failed. One or more conditions in the request fields evaluated to false against the current resource state.

  68. Карточка 68

    Вопрос

    What does HTTP status code 511 mean?

    Ответ

    Network Authentication Required. The client must authenticate to gain network access. It is intended for an intercepting proxy, such as a captive portal, not an origin server.

  69. Карточка 69

    Вопрос

    What does HTTP status code 413 mean?

    Ответ

    Content Too Large. The server refuses to process the request because its content is larger than the server is willing or able to process.

  70. Карточка 70

    Вопрос

    What does HTTP status code 411 mean?

    Ответ

    Length Required. The server refuses the request without a defined Content-Length; the client can retry with a valid value.

  71. Карточка 71

    Вопрос

    Which HTTP status code means a request precondition evaluated to false?

    Ответ

    412 Precondition Failed. The method is not applied when the stated condition does not match the resource’s current state.

  72. Карточка 72

    Вопрос

    Which HTTP status code asks the client to authenticate for network access rather than to the origin server?

    Ответ

    511 Network Authentication Required. It is designed for intercepting network proxies such as captive portals.

  73. Карточка 73

    Вопрос

    What does HTTP status code 414 mean?

    Ответ

    URI Too Long. The server refuses the request because the target URI is longer than it is willing to interpret.

  74. Карточка 74

    Вопрос

    Which HTTP status code means the request content is too large to process?

    Ответ

    413 Content Too Large. The refusal is about the size of the request content, not the URI or request headers.

  75. Карточка 75

    Вопрос

    What does HTTP status code 415 mean?

    Ответ

    Unsupported Media Type. The origin server refuses the request because its content format is unsupported for this method on the target resource.

  76. Карточка 76

    Вопрос

    What does HTTP status code 416 mean?

    Ответ

    Range Not Satisfiable. The requested ranges were rejected because none can be satisfied or because the request contains too many small or overlapping ranges.

  77. Карточка 77

    Вопрос

    What does HTTP status code 422 mean?

    Ответ

    Unprocessable Content. The server understands the content type and the syntax is correct, but it cannot process the contained instructions.

  78. Карточка 78

    Вопрос

    What does HTTP status code 417 mean?

    Ответ

    Expectation Failed. At least one inbound server could not meet the expectation stated in the request’s Expect field.

  79. Карточка 79

    Вопрос

    Which HTTP status code means the request content format is unsupported for the target method?

    Ответ

    415 Unsupported Media Type. The issue can come from Content-Type, Content-Encoding, or inspecting the data itself.

  80. Карточка 80

    Вопрос

    What does HTTP status code 421 mean?

    Ответ

    Misdirected Request. The request reached a server that cannot or will not produce an authoritative response for that target URI on the received connection.

  81. Карточка 81

    Вопрос

    What does HTTP status code 423 mean?

    Ответ

    Locked. In WebDAV, the source or destination resource for the method is locked.

  82. Карточка 82

    Вопрос

    Which HTTP status code means syntactically correct content cannot be processed?

    Ответ

    422 Unprocessable Content. The content type is understood and the syntax is valid, but the contained instructions cannot be processed.

  83. Карточка 83

    Вопрос

    What does HTTP status code 424 mean?

    Ответ

    Failed Dependency. The requested action depended on another action, and that other action failed.

  84. Карточка 84

    Вопрос

    What does HTTP status code 425 mean?

    Ответ

    Too Early. The server is unwilling to risk processing a request that might be replayed, such as a request sent in TLS early data.

  85. Карточка 85

    Вопрос

    What does HTTP status code 429 mean?

    Ответ

    Too Many Requests. The user sent too many requests in a given time. The response may include Retry-After.

  86. Карточка 86

    Вопрос

    What does HTTP status code 426 mean?

    Ответ

    Upgrade Required. The server refuses the current protocol but might perform the request after the client upgrades. The response states the required protocol in Upgrade.

  87. Карточка 87

    Вопрос

    What does HTTP status code 428 mean?

    Ответ

    Precondition Required. The origin server requires a conditional request, commonly to prevent a lost update when resource state changes between reading and writing.

  88. Карточка 88

    Вопрос

    What does HTTP status code 431 mean?

    Ответ

    Request Header Fields Too Large. The server refuses to process the request because all request headers together, or one particular header, are too large.

  89. Карточка 89

    Вопрос

    Which HTTP status code is registered for rate limiting?

    Ответ

    429 Too Many Requests. It indicates too many requests in a given amount of time.

  90. Карточка 90

    Вопрос

    What does HTTP status code 451 mean?

    Ответ

    Unavailable For Legal Reasons. Access is denied because of a legal demand. The code does not establish whether the resource exists.

  91. Карточка 91

    Вопрос

    How do HTTP 401 and 403 differ?

    Ответ

    401 Unauthorized means the request lacks valid authentication credentials and includes an authentication challenge. 403 Forbidden means the server understood the request but refuses it; credentials may be insufficient or irrelevant to the refusal.

  92. Карточка 92

    Вопрос

    How do HTTP 301, 302, 307, and 308 differ?

    Ответ

    301 is permanent and may change POST to GET. 302 is temporary and may change POST to GET. 307 is temporary and preserves the method. 308 is permanent and preserves the method.

  93. Карточка 93

    Вопрос

    How do HTTP 409 and 422 differ?

    Ответ

    409 Conflict is about a conflict with the target resource’s current state. 422 Unprocessable Content is about understood, syntactically correct request content whose instructions cannot be processed. Neither code dictates one universal REST API policy.

  94. Карточка 94

    Вопрос

    Which HTTP status code means access is denied because of a legal demand?

    Ответ

    451 Unavailable For Legal Reasons. The response can explain the legal demand and who it affects.

  95. Карточка 95

    Вопрос

    How do HTTP 404 and 410 differ?

    Ответ

    404 Not Found does not say whether the missing representation is temporary or permanent and can also hide a resource’s existence. 410 Gone says the resource is no longer available and the condition is likely permanent.

  96. Карточка 96

    Вопрос

    How do HTTP 202 and 204 differ?

    Ответ

    202 Accepted means processing was accepted but is not complete and may never happen. 204 No Content means the request was successfully fulfilled and there is no additional response content.

  97. Карточка 97

    Вопрос

    How do HTTP 502 and 504 differ?

    Ответ

    502 Bad Gateway means the gateway or proxy received an invalid upstream response. 504 Gateway Timeout means it did not receive the needed upstream response in time.

  98. Карточка 98

    Вопрос

    What does HTTP status code 104 mean, and what is its registry status?

    Ответ

    Upload Resumption Supported — temporary. It is an informational response indicating resumable-upload support. IANA records registration on 13 November 2024, an extension on 15 September 2025, and expiry on 13 November 2026.

  99. Карточка 99

    Вопрос

    What does HTTP status code 402 mean?

    Ответ

    Payment Required — reserved for future use. IANA registers the reason phrase, but RFC 9110 does not define a general operational meaning. Treat application-specific payment uses as conventions, not universal HTTP semantics.

  100. Карточка 100

    Вопрос

    What is the current registry status of HTTP 306?

    Ответ

    Unused and reserved. RFC 9110 says 306 was defined previously, is no longer used, and remains reserved. It is not an ordinary redirect code.

  101. Карточка 101

    Вопрос

    What is the current registry status of HTTP 418?

    Ответ

    Unused and reserved. IANA does not register “I’m a Teapot” as the current reason phrase. RFC 9110 keeps 418 unavailable for other assignments because the joke code was widely deployed.

  102. Карточка 102

    Вопрос

    What is the current registry status of HTTP 510?

    Ответ

    Not Extended — obsoleted. The historical code said an extension policy was not met, but IANA marks it obsoleted after the HTTP extension experiments moved to Historic status.

Abstract glowing network paths connecting two endpoint forms around a central response pulse on a dark background.

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HTTP Status Code Flashcards: Meanings, Classes & Use Cases

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