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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 whenLocationis absent.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-Authenticatechallenge.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.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.
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.
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.
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.
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.
Carta 18
Domanda
Which HTTP status code has the registered reason phrase “OK”?
Risposta
200 OK. It indicates that the request succeeded.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Carta 31
Domanda
Which HTTP status code has the registered reason phrase “Accepted”?
Risposta
202 Accepted. Processing has been accepted but is not complete.
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.
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.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.
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.
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.
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.
Carta 38
Domanda
What does HTTP status code 101 mean?
Risposta
Switching Protocols. The server accepts the client’s
Upgraderequest and names the protocol that will be used after this response.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.
Carta 40
Domanda
Which temporary redirect status code requires method preservation?
Risposta
307 Temporary Redirect. An automatic redirect must not change the request method.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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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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.
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.
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.
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
Allowfield.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.
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.
Carta 58
Domanda
What does HTTP status code 303 mean?
Risposta
See Other. The
LocationURI identifies a different resource that can provide an indirect response; the user agent retrieves it with GET or HEAD.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.
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.
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
IMresponse field.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.
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-Authenticatechallenge.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.
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.
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: infinityrequest.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.
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.
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.
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.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.
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.
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.
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.
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.
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.
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.
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
Expectfield.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.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.
Carta 81
Domanda
What does HTTP status code 423 mean?
Risposta
Locked. In WebDAV, the source or destination resource for the method is locked.
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.
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.
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.
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.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.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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
102 carte
HTTP Status Code Flashcards: Meanings, Classes & Use Cases
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