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 este mazo

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.

Tarjetas de este mazo

  1. Tarjeta 1

    Pregunta

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

    Respuesta

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

  2. Tarjeta 2

    Pregunta

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

    Respuesta

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

  3. Tarjeta 3

    Pregunta

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

    Respuesta

    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. Tarjeta 4

    Pregunta

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

    Respuesta

    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. Tarjeta 5

    Pregunta

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

    Respuesta

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

  6. Tarjeta 6

    Pregunta

    What does HTTP status code 200 mean?

    Respuesta

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

  7. Tarjeta 7

    Pregunta

    What does HTTP status code 404 mean?

    Respuesta

    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. Tarjeta 8

    Pregunta

    What does HTTP status code 301 mean?

    Respuesta

    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. Tarjeta 9

    Pregunta

    What does HTTP status code 500 mean?

    Respuesta

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

  10. Tarjeta 10

    Pregunta

    What does HTTP status code 201 mean?

    Respuesta

    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. Tarjeta 11

    Pregunta

    What does HTTP status code 401 mean?

    Respuesta

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

  12. Tarjeta 12

    Pregunta

    What does HTTP status code 503 mean?

    Respuesta

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

  13. Tarjeta 13

    Pregunta

    What does HTTP status code 204 mean?

    Respuesta

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

  14. Tarjeta 14

    Pregunta

    What does HTTP status code 403 mean?

    Respuesta

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

  15. Tarjeta 15

    Pregunta

    What does HTTP status code 302 mean?

    Respuesta

    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. Tarjeta 16

    Pregunta

    What does HTTP status code 400 mean?

    Respuesta

    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. Tarjeta 17

    Pregunta

    What does HTTP status code 502 mean?

    Respuesta

    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. Tarjeta 18

    Pregunta

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

    Respuesta

    200 OK. It indicates that the request succeeded.

  19. Tarjeta 19

    Pregunta

    What does HTTP status code 202 mean?

    Respuesta

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

  20. Tarjeta 20

    Pregunta

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

    Respuesta

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

  21. Tarjeta 21

    Pregunta

    What does HTTP status code 304 mean?

    Respuesta

    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. Tarjeta 22

    Pregunta

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

    Respuesta

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

  23. Tarjeta 23

    Pregunta

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

    Respuesta

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

  24. Tarjeta 24

    Pregunta

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

    Respuesta

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

  25. Tarjeta 25

    Pregunta

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

    Respuesta

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

  26. Tarjeta 26

    Pregunta

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

    Respuesta

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

  27. Tarjeta 27

    Pregunta

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

    Respuesta

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

  28. Tarjeta 28

    Pregunta

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

    Respuesta

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

  29. Tarjeta 29

    Pregunta

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

    Respuesta

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

  30. Tarjeta 30

    Pregunta

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

    Respuesta

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

  31. Tarjeta 31

    Pregunta

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

    Respuesta

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

  32. Tarjeta 32

    Pregunta

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

    Respuesta

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

  33. Tarjeta 33

    Pregunta

    What does HTTP status code 100 mean?

    Respuesta

    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. Tarjeta 34

    Pregunta

    What does HTTP status code 206 mean?

    Respuesta

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

  35. Tarjeta 35

    Pregunta

    What does HTTP status code 307 mean?

    Respuesta

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

  36. Tarjeta 36

    Pregunta

    What does HTTP status code 409 mean?

    Respuesta

    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. Tarjeta 37

    Pregunta

    What does HTTP status code 504 mean?

    Respuesta

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

  38. Tarjeta 38

    Pregunta

    What does HTTP status code 101 mean?

    Respuesta

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

  39. Tarjeta 39

    Pregunta

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

    Respuesta

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

  40. Tarjeta 40

    Pregunta

    Which temporary redirect status code requires method preservation?

    Respuesta

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

  41. Tarjeta 41

    Pregunta

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

    Respuesta

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

  42. Tarjeta 42

    Pregunta

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

    Respuesta

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

  43. Tarjeta 43

    Pregunta

    What does HTTP status code 102 mean?

    Respuesta

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

  44. Tarjeta 44

    Pregunta

    What does HTTP status code 203 mean?

    Respuesta

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

  45. Tarjeta 45

    Pregunta

    What does HTTP status code 308 mean?

    Respuesta

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

  46. Tarjeta 46

    Pregunta

    What does HTTP status code 410 mean?

    Respuesta

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

  47. Tarjeta 47

    Pregunta

    What does HTTP status code 501 mean?

    Respuesta

    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. Tarjeta 48

    Pregunta

    What does HTTP status code 103 mean?

    Respuesta

    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. Tarjeta 49

    Pregunta

    What does HTTP status code 205 mean?

    Respuesta

    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. Tarjeta 50

    Pregunta

    Which permanent redirect status code requires method preservation?

    Respuesta

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

  51. Tarjeta 51

    Pregunta

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

    Respuesta

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

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  52. Tarjeta 52

    Pregunta

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

    Respuesta

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

  53. Tarjeta 53

    Pregunta

    What does HTTP status code 207 mean?

    Respuesta

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

  54. Tarjeta 54

    Pregunta

    What does HTTP status code 300 mean?

    Respuesta

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

  55. Tarjeta 55

    Pregunta

    What does HTTP status code 405 mean?

    Respuesta

    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. Tarjeta 56

    Pregunta

    What does HTTP status code 505 mean?

    Respuesta

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

  57. Tarjeta 57

    Pregunta

    What does HTTP status code 208 mean?

    Respuesta

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

  58. Tarjeta 58

    Pregunta

    What does HTTP status code 303 mean?

    Respuesta

    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. Tarjeta 59

    Pregunta

    What does HTTP status code 406 mean?

    Respuesta

    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. Tarjeta 60

    Pregunta

    What does HTTP status code 506 mean?

    Respuesta

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

  61. Tarjeta 61

    Pregunta

    What does HTTP status code 226 mean?

    Respuesta

    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. Tarjeta 62

    Pregunta

    What does HTTP status code 305 mean?

    Respuesta

    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. Tarjeta 63

    Pregunta

    What does HTTP status code 407 mean?

    Respuesta

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

  64. Tarjeta 64

    Pregunta

    What does HTTP status code 507 mean?

    Respuesta

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

  65. Tarjeta 65

    Pregunta

    What does HTTP status code 408 mean?

    Respuesta

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

  66. Tarjeta 66

    Pregunta

    What does HTTP status code 508 mean?

    Respuesta

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

  67. Tarjeta 67

    Pregunta

    What does HTTP status code 412 mean?

    Respuesta

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

  68. Tarjeta 68

    Pregunta

    What does HTTP status code 511 mean?

    Respuesta

    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. Tarjeta 69

    Pregunta

    What does HTTP status code 413 mean?

    Respuesta

    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. Tarjeta 70

    Pregunta

    What does HTTP status code 411 mean?

    Respuesta

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

  71. Tarjeta 71

    Pregunta

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

    Respuesta

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

  72. Tarjeta 72

    Pregunta

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

    Respuesta

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

  73. Tarjeta 73

    Pregunta

    What does HTTP status code 414 mean?

    Respuesta

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

  74. Tarjeta 74

    Pregunta

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

    Respuesta

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

  75. Tarjeta 75

    Pregunta

    What does HTTP status code 415 mean?

    Respuesta

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

  76. Tarjeta 76

    Pregunta

    What does HTTP status code 416 mean?

    Respuesta

    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. Tarjeta 77

    Pregunta

    What does HTTP status code 422 mean?

    Respuesta

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

  78. Tarjeta 78

    Pregunta

    What does HTTP status code 417 mean?

    Respuesta

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

  79. Tarjeta 79

    Pregunta

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

    Respuesta

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

  80. Tarjeta 80

    Pregunta

    What does HTTP status code 421 mean?

    Respuesta

    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. Tarjeta 81

    Pregunta

    What does HTTP status code 423 mean?

    Respuesta

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

  82. Tarjeta 82

    Pregunta

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

    Respuesta

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

  83. Tarjeta 83

    Pregunta

    What does HTTP status code 424 mean?

    Respuesta

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

  84. Tarjeta 84

    Pregunta

    What does HTTP status code 425 mean?

    Respuesta

    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. Tarjeta 85

    Pregunta

    What does HTTP status code 429 mean?

    Respuesta

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

  86. Tarjeta 86

    Pregunta

    What does HTTP status code 426 mean?

    Respuesta

    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. Tarjeta 87

    Pregunta

    What does HTTP status code 428 mean?

    Respuesta

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

  88. Tarjeta 88

    Pregunta

    What does HTTP status code 431 mean?

    Respuesta

    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. Tarjeta 89

    Pregunta

    Which HTTP status code is registered for rate limiting?

    Respuesta

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

  90. Tarjeta 90

    Pregunta

    What does HTTP status code 451 mean?

    Respuesta

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

  91. Tarjeta 91

    Pregunta

    How do HTTP 401 and 403 differ?

    Respuesta

    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. Tarjeta 92

    Pregunta

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

    Respuesta

    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. Tarjeta 93

    Pregunta

    How do HTTP 409 and 422 differ?

    Respuesta

    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. Tarjeta 94

    Pregunta

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

    Respuesta

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

  95. Tarjeta 95

    Pregunta

    How do HTTP 404 and 410 differ?

    Respuesta

    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. Tarjeta 96

    Pregunta

    How do HTTP 202 and 204 differ?

    Respuesta

    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. Tarjeta 97

    Pregunta

    How do HTTP 502 and 504 differ?

    Respuesta

    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. Tarjeta 98

    Pregunta

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

    Respuesta

    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. Tarjeta 99

    Pregunta

    What does HTTP status code 402 mean?

    Respuesta

    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. Tarjeta 100

    Pregunta

    What is the current registry status of HTTP 306?

    Respuesta

    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. Tarjeta 101

    Pregunta

    What is the current registry status of HTTP 418?

    Respuesta

    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. Tarjeta 102

    Pregunta

    What is the current registry status of HTTP 510?

    Respuesta

    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.

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HTTP Status Code Flashcards: Meanings, Classes & Use Cases

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