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.

Informazioni su questo mazzo

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.

Carte in questo mazzo

  1. Carta 1

    Domanda

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

    Risposta

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

  2. Carta 2

    Domanda

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

    Risposta

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

  3. Carta 3

    Domanda

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

    Risposta

    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. Carta 4

    Domanda

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

    Risposta

    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. Carta 5

    Domanda

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

    Risposta

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

  6. Carta 6

    Domanda

    What does HTTP status code 200 mean?

    Risposta

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

  7. Carta 7

    Domanda

    What does HTTP status code 404 mean?

    Risposta

    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. Carta 8

    Domanda

    What does HTTP status code 301 mean?

    Risposta

    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. Carta 9

    Domanda

    What does HTTP status code 500 mean?

    Risposta

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

  10. Carta 10

    Domanda

    What does HTTP status code 201 mean?

    Risposta

    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. Carta 11

    Domanda

    What does HTTP status code 401 mean?

    Risposta

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

  12. Carta 12

    Domanda

    What does HTTP status code 503 mean?

    Risposta

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

  13. Carta 13

    Domanda

    What does HTTP status code 204 mean?

    Risposta

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

  14. Carta 14

    Domanda

    What does HTTP status code 403 mean?

    Risposta

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

  15. Carta 15

    Domanda

    What does HTTP status code 302 mean?

    Risposta

    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. Carta 16

    Domanda

    What does HTTP status code 400 mean?

    Risposta

    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. Carta 17

    Domanda

    What does HTTP status code 502 mean?

    Risposta

    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. Carta 18

    Domanda

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

    Risposta

    200 OK. It indicates that the request succeeded.

  19. Carta 19

    Domanda

    What does HTTP status code 202 mean?

    Risposta

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

  20. Carta 20

    Domanda

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

    Risposta

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

  21. Carta 21

    Domanda

    What does HTTP status code 304 mean?

    Risposta

    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. Carta 22

    Domanda

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

    Risposta

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

  23. Carta 23

    Domanda

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

    Risposta

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

  24. Carta 24

    Domanda

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

    Risposta

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

  25. Carta 25

    Domanda

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

    Risposta

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

  26. Carta 26

    Domanda

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

    Risposta

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

  27. Carta 27

    Domanda

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

    Risposta

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

  28. Carta 28

    Domanda

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

    Risposta

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

  29. Carta 29

    Domanda

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

    Risposta

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

  30. Carta 30

    Domanda

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

    Risposta

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

  31. Carta 31

    Domanda

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

    Risposta

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

  32. Carta 32

    Domanda

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

    Risposta

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

  33. Carta 33

    Domanda

    What does HTTP status code 100 mean?

    Risposta

    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. Carta 34

    Domanda

    What does HTTP status code 206 mean?

    Risposta

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

  35. Carta 35

    Domanda

    What does HTTP status code 307 mean?

    Risposta

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

  36. Carta 36

    Domanda

    What does HTTP status code 409 mean?

    Risposta

    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. Carta 37

    Domanda

    What does HTTP status code 504 mean?

    Risposta

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

  38. Carta 38

    Domanda

    What does HTTP status code 101 mean?

    Risposta

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

  39. Carta 39

    Domanda

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

    Risposta

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

  40. Carta 40

    Domanda

    Which temporary redirect status code requires method preservation?

    Risposta

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

  41. Carta 41

    Domanda

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

    Risposta

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

  42. Carta 42

    Domanda

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

    Risposta

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

  43. Carta 43

    Domanda

    What does HTTP status code 102 mean?

    Risposta

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

  44. Carta 44

    Domanda

    What does HTTP status code 203 mean?

    Risposta

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

  45. Carta 45

    Domanda

    What does HTTP status code 308 mean?

    Risposta

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

  46. Carta 46

    Domanda

    What does HTTP status code 410 mean?

    Risposta

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

  47. Carta 47

    Domanda

    What does HTTP status code 501 mean?

    Risposta

    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. Carta 48

    Domanda

    What does HTTP status code 103 mean?

    Risposta

    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. Carta 49

    Domanda

    What does HTTP status code 205 mean?

    Risposta

    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. Carta 50

    Domanda

    Which permanent redirect status code requires method preservation?

    Risposta

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

  51. Carta 51

    Domanda

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

    Risposta

    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. Carta 52

    Domanda

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

    Risposta

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

  53. Carta 53

    Domanda

    What does HTTP status code 207 mean?

    Risposta

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

  54. Carta 54

    Domanda

    What does HTTP status code 300 mean?

    Risposta

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

  55. Carta 55

    Domanda

    What does HTTP status code 405 mean?

    Risposta

    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. Carta 56

    Domanda

    What does HTTP status code 505 mean?

    Risposta

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

  57. Carta 57

    Domanda

    What does HTTP status code 208 mean?

    Risposta

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

  58. Carta 58

    Domanda

    What does HTTP status code 303 mean?

    Risposta

    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. Carta 59

    Domanda

    What does HTTP status code 406 mean?

    Risposta

    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. Carta 60

    Domanda

    What does HTTP status code 506 mean?

    Risposta

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

  61. Carta 61

    Domanda

    What does HTTP status code 226 mean?

    Risposta

    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. Carta 62

    Domanda

    What does HTTP status code 305 mean?

    Risposta

    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. Carta 63

    Domanda

    What does HTTP status code 407 mean?

    Risposta

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

  64. Carta 64

    Domanda

    What does HTTP status code 507 mean?

    Risposta

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

  65. Carta 65

    Domanda

    What does HTTP status code 408 mean?

    Risposta

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

  66. Carta 66

    Domanda

    What does HTTP status code 508 mean?

    Risposta

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

  67. Carta 67

    Domanda

    What does HTTP status code 412 mean?

    Risposta

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

  68. Carta 68

    Domanda

    What does HTTP status code 511 mean?

    Risposta

    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. Carta 69

    Domanda

    What does HTTP status code 413 mean?

    Risposta

    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. Carta 70

    Domanda

    What does HTTP status code 411 mean?

    Risposta

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

  71. Carta 71

    Domanda

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

    Risposta

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

  72. Carta 72

    Domanda

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

    Risposta

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

  73. Carta 73

    Domanda

    What does HTTP status code 414 mean?

    Risposta

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

  74. Carta 74

    Domanda

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

    Risposta

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

  75. Carta 75

    Domanda

    What does HTTP status code 415 mean?

    Risposta

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

  76. Carta 76

    Domanda

    What does HTTP status code 416 mean?

    Risposta

    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. Carta 77

    Domanda

    What does HTTP status code 422 mean?

    Risposta

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

  78. Carta 78

    Domanda

    What does HTTP status code 417 mean?

    Risposta

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

  79. Carta 79

    Domanda

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

    Risposta

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

  80. Carta 80

    Domanda

    What does HTTP status code 421 mean?

    Risposta

    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. Carta 81

    Domanda

    What does HTTP status code 423 mean?

    Risposta

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

  82. Carta 82

    Domanda

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

    Risposta

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

  83. Carta 83

    Domanda

    What does HTTP status code 424 mean?

    Risposta

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

  84. Carta 84

    Domanda

    What does HTTP status code 425 mean?

    Risposta

    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. Carta 85

    Domanda

    What does HTTP status code 429 mean?

    Risposta

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

  86. Carta 86

    Domanda

    What does HTTP status code 426 mean?

    Risposta

    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. Carta 87

    Domanda

    What does HTTP status code 428 mean?

    Risposta

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

  88. Carta 88

    Domanda

    What does HTTP status code 431 mean?

    Risposta

    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. Carta 89

    Domanda

    Which HTTP status code is registered for rate limiting?

    Risposta

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

  90. Carta 90

    Domanda

    What does HTTP status code 451 mean?

    Risposta

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

  91. Carta 91

    Domanda

    How do HTTP 401 and 403 differ?

    Risposta

    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. Carta 92

    Domanda

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

    Risposta

    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. Carta 93

    Domanda

    How do HTTP 409 and 422 differ?

    Risposta

    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. Carta 94

    Domanda

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

    Risposta

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

  95. Carta 95

    Domanda

    How do HTTP 404 and 410 differ?

    Risposta

    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. Carta 96

    Domanda

    How do HTTP 202 and 204 differ?

    Risposta

    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. Carta 97

    Domanda

    How do HTTP 502 and 504 differ?

    Risposta

    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. Carta 98

    Domanda

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

    Risposta

    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. Carta 99

    Domanda

    What does HTTP status code 402 mean?

    Risposta

    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. Carta 100

    Domanda

    What is the current registry status of HTTP 306?

    Risposta

    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. Carta 101

    Domanda

    What is the current registry status of HTTP 418?

    Risposta

    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. Carta 102

    Domanda

    What is the current registry status of HTTP 510?

    Risposta

    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.

102 carte

HTTP Status Code Flashcards: Meanings, Classes & Use Cases

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