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.

Sobre aquesta baralla

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.

Targetes d'aquesta baralla

  1. Targeta 1

    Pregunta

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

    Resposta

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

  2. Targeta 2

    Pregunta

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

    Resposta

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

  3. Targeta 3

    Pregunta

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

    Resposta

    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. Targeta 4

    Pregunta

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

    Resposta

    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. Targeta 5

    Pregunta

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

    Resposta

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

  6. Targeta 6

    Pregunta

    What does HTTP status code 200 mean?

    Resposta

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

  7. Targeta 7

    Pregunta

    What does HTTP status code 404 mean?

    Resposta

    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. Targeta 8

    Pregunta

    What does HTTP status code 301 mean?

    Resposta

    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. Targeta 9

    Pregunta

    What does HTTP status code 500 mean?

    Resposta

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

  10. Targeta 10

    Pregunta

    What does HTTP status code 201 mean?

    Resposta

    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. Targeta 11

    Pregunta

    What does HTTP status code 401 mean?

    Resposta

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

  12. Targeta 12

    Pregunta

    What does HTTP status code 503 mean?

    Resposta

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

  13. Targeta 13

    Pregunta

    What does HTTP status code 204 mean?

    Resposta

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

  14. Targeta 14

    Pregunta

    What does HTTP status code 403 mean?

    Resposta

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

  15. Targeta 15

    Pregunta

    What does HTTP status code 302 mean?

    Resposta

    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. Targeta 16

    Pregunta

    What does HTTP status code 400 mean?

    Resposta

    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. Targeta 17

    Pregunta

    What does HTTP status code 502 mean?

    Resposta

    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. Targeta 18

    Pregunta

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

    Resposta

    200 OK. It indicates that the request succeeded.

  19. Targeta 19

    Pregunta

    What does HTTP status code 202 mean?

    Resposta

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

  20. Targeta 20

    Pregunta

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

    Resposta

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

  21. Targeta 21

    Pregunta

    What does HTTP status code 304 mean?

    Resposta

    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. Targeta 22

    Pregunta

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

    Resposta

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

  23. Targeta 23

    Pregunta

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

    Resposta

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

  24. Targeta 24

    Pregunta

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

    Resposta

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

  25. Targeta 25

    Pregunta

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

    Resposta

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

  26. Targeta 26

    Pregunta

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

    Resposta

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

  27. Targeta 27

    Pregunta

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

    Resposta

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

  28. Targeta 28

    Pregunta

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

    Resposta

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

  29. Targeta 29

    Pregunta

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

    Resposta

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

  30. Targeta 30

    Pregunta

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

    Resposta

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

  31. Targeta 31

    Pregunta

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

    Resposta

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

  32. Targeta 32

    Pregunta

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

    Resposta

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

  33. Targeta 33

    Pregunta

    What does HTTP status code 100 mean?

    Resposta

    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. Targeta 34

    Pregunta

    What does HTTP status code 206 mean?

    Resposta

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

  35. Targeta 35

    Pregunta

    What does HTTP status code 307 mean?

    Resposta

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

  36. Targeta 36

    Pregunta

    What does HTTP status code 409 mean?

    Resposta

    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. Targeta 37

    Pregunta

    What does HTTP status code 504 mean?

    Resposta

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

  38. Targeta 38

    Pregunta

    What does HTTP status code 101 mean?

    Resposta

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

  39. Targeta 39

    Pregunta

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

    Resposta

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

  40. Targeta 40

    Pregunta

    Which temporary redirect status code requires method preservation?

    Resposta

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

  41. Targeta 41

    Pregunta

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

    Resposta

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

  42. Targeta 42

    Pregunta

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

    Resposta

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

  43. Targeta 43

    Pregunta

    What does HTTP status code 102 mean?

    Resposta

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

  44. Targeta 44

    Pregunta

    What does HTTP status code 203 mean?

    Resposta

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

  45. Targeta 45

    Pregunta

    What does HTTP status code 308 mean?

    Resposta

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

  46. Targeta 46

    Pregunta

    What does HTTP status code 410 mean?

    Resposta

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

  47. Targeta 47

    Pregunta

    What does HTTP status code 501 mean?

    Resposta

    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. Targeta 48

    Pregunta

    What does HTTP status code 103 mean?

    Resposta

    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. Targeta 49

    Pregunta

    What does HTTP status code 205 mean?

    Resposta

    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. Targeta 50

    Pregunta

    Which permanent redirect status code requires method preservation?

    Resposta

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

  51. Targeta 51

    Pregunta

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

    Resposta

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

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    102 targetes

    HTTP Status Code Flashcards: Meanings, Classes & Use Cases

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  52. Targeta 52

    Pregunta

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

    Resposta

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

  53. Targeta 53

    Pregunta

    What does HTTP status code 207 mean?

    Resposta

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

  54. Targeta 54

    Pregunta

    What does HTTP status code 300 mean?

    Resposta

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

  55. Targeta 55

    Pregunta

    What does HTTP status code 405 mean?

    Resposta

    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. Targeta 56

    Pregunta

    What does HTTP status code 505 mean?

    Resposta

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

  57. Targeta 57

    Pregunta

    What does HTTP status code 208 mean?

    Resposta

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

  58. Targeta 58

    Pregunta

    What does HTTP status code 303 mean?

    Resposta

    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. Targeta 59

    Pregunta

    What does HTTP status code 406 mean?

    Resposta

    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. Targeta 60

    Pregunta

    What does HTTP status code 506 mean?

    Resposta

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

  61. Targeta 61

    Pregunta

    What does HTTP status code 226 mean?

    Resposta

    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. Targeta 62

    Pregunta

    What does HTTP status code 305 mean?

    Resposta

    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. Targeta 63

    Pregunta

    What does HTTP status code 407 mean?

    Resposta

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

  64. Targeta 64

    Pregunta

    What does HTTP status code 507 mean?

    Resposta

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

  65. Targeta 65

    Pregunta

    What does HTTP status code 408 mean?

    Resposta

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

  66. Targeta 66

    Pregunta

    What does HTTP status code 508 mean?

    Resposta

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

  67. Targeta 67

    Pregunta

    What does HTTP status code 412 mean?

    Resposta

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

  68. Targeta 68

    Pregunta

    What does HTTP status code 511 mean?

    Resposta

    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. Targeta 69

    Pregunta

    What does HTTP status code 413 mean?

    Resposta

    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. Targeta 70

    Pregunta

    What does HTTP status code 411 mean?

    Resposta

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

  71. Targeta 71

    Pregunta

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

    Resposta

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

  72. Targeta 72

    Pregunta

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

    Resposta

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

  73. Targeta 73

    Pregunta

    What does HTTP status code 414 mean?

    Resposta

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

  74. Targeta 74

    Pregunta

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

    Resposta

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

  75. Targeta 75

    Pregunta

    What does HTTP status code 415 mean?

    Resposta

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

  76. Targeta 76

    Pregunta

    What does HTTP status code 416 mean?

    Resposta

    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. Targeta 77

    Pregunta

    What does HTTP status code 422 mean?

    Resposta

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

  78. Targeta 78

    Pregunta

    What does HTTP status code 417 mean?

    Resposta

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

  79. Targeta 79

    Pregunta

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

    Resposta

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

  80. Targeta 80

    Pregunta

    What does HTTP status code 421 mean?

    Resposta

    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. Targeta 81

    Pregunta

    What does HTTP status code 423 mean?

    Resposta

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

  82. Targeta 82

    Pregunta

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

    Resposta

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

  83. Targeta 83

    Pregunta

    What does HTTP status code 424 mean?

    Resposta

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

  84. Targeta 84

    Pregunta

    What does HTTP status code 425 mean?

    Resposta

    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. Targeta 85

    Pregunta

    What does HTTP status code 429 mean?

    Resposta

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

  86. Targeta 86

    Pregunta

    What does HTTP status code 426 mean?

    Resposta

    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. Targeta 87

    Pregunta

    What does HTTP status code 428 mean?

    Resposta

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

  88. Targeta 88

    Pregunta

    What does HTTP status code 431 mean?

    Resposta

    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. Targeta 89

    Pregunta

    Which HTTP status code is registered for rate limiting?

    Resposta

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

  90. Targeta 90

    Pregunta

    What does HTTP status code 451 mean?

    Resposta

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

  91. Targeta 91

    Pregunta

    How do HTTP 401 and 403 differ?

    Resposta

    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. Targeta 92

    Pregunta

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

    Resposta

    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. Targeta 93

    Pregunta

    How do HTTP 409 and 422 differ?

    Resposta

    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. Targeta 94

    Pregunta

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

    Resposta

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

  95. Targeta 95

    Pregunta

    How do HTTP 404 and 410 differ?

    Resposta

    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. Targeta 96

    Pregunta

    How do HTTP 202 and 204 differ?

    Resposta

    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. Targeta 97

    Pregunta

    How do HTTP 502 and 504 differ?

    Resposta

    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. Targeta 98

    Pregunta

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

    Resposta

    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. Targeta 99

    Pregunta

    What does HTTP status code 402 mean?

    Resposta

    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. Targeta 100

    Pregunta

    What is the current registry status of HTTP 306?

    Resposta

    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. Targeta 101

    Pregunta

    What is the current registry status of HTTP 418?

    Resposta

    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. Targeta 102

    Pregunta

    What is the current registry status of HTTP 510?

    Resposta

    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 targetes

HTTP Status Code Flashcards: Meanings, Classes & Use Cases

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