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.
About this deck
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.
Cards in this deck
Card 1
Question
What is the purpose of the 1xx HTTP status-code class?
Answer
Informational. A 1xx response is interim: it communicates connection status or request progress before the final response.
Card 2
Question
What is the purpose of the 2xx HTTP status-code class?
Answer
Successful. A 2xx response means the request was successfully received, understood, and accepted.
Card 3
Question
What is the purpose of the 3xx HTTP status-code class?
Answer
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.
Card 4
Question
What is the purpose of the 4xx HTTP status-code class?
Answer
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.
Card 5
Question
What is the purpose of the 5xx HTTP status-code class?
Answer
Server Error. A 5xx response means the server knows it has erred or cannot perform the requested method.
Card 6
Question
What does HTTP status code 200 mean?
Answer
OK. The request succeeded; the meaning of any response content depends on the request method.
Card 7
Question
What does HTTP status code 404 mean?
Answer
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.
Card 8
Question
What does HTTP status code 301 mean?
Answer
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.
Card 9
Question
What does HTTP status code 500 mean?
Answer
Internal Server Error. The server hit an unexpected condition that prevented it from fulfilling the request.
Card 10
Question
What does HTTP status code 201 mean?
Answer
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.Card 11
Question
What does HTTP status code 401 mean?
Answer
Unauthorized. The request was not applied because it lacks valid authentication credentials for the target resource. The response includes a
WWW-Authenticatechallenge.Card 12
Question
What does HTTP status code 503 mean?
Answer
Service Unavailable. The server is temporarily unable to handle the request, often because of overload or maintenance. It may send
Retry-After.Card 13
Question
What does HTTP status code 204 mean?
Answer
No Content. The server successfully fulfilled the request and has no additional response content to send.
Card 14
Question
What does HTTP status code 403 mean?
Answer
Forbidden. The server understood the request but refuses to fulfill it. Credentials may be insufficient, or the refusal may be unrelated to authentication.
Card 15
Question
What does HTTP status code 302 mean?
Answer
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.
Card 16
Question
What does HTTP status code 400 mean?
Answer
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.
Card 17
Question
What does HTTP status code 502 mean?
Answer
Bad Gateway. A server acting as a gateway or proxy received an invalid response from an inbound server while trying to fulfill the request.
Card 18
Question
Which HTTP status code has the registered reason phrase “OK”?
Answer
200 OK. It indicates that the request succeeded.
Card 19
Question
What does HTTP status code 202 mean?
Answer
Accepted. The request was accepted for processing, but processing is incomplete and might not ultimately happen.
Card 20
Question
Which HTTP status code has the registered reason phrase “Not Found”?
Answer
404 Not Found. It means there is no current representation for the target resource, or the server will not disclose one.
Card 21
Question
What does HTTP status code 304 mean?
Answer
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.
Card 22
Question
Which HTTP status code has the registered reason phrase “Created”?
Answer
201 Created. It means the fulfilled request created one or more resources.
Card 23
Question
Which HTTP status code means the request lacks valid authentication credentials?
Answer
401 Unauthorized. The response challenges the client to authenticate for the target resource.
Card 24
Question
Which HTTP status code has the registered reason phrase “Internal Server Error”?
Answer
500 Internal Server Error. It covers an unexpected server condition that prevented fulfillment.
Card 25
Question
Which HTTP status code means success with no additional response content?
Answer
204 No Content. The action succeeded, and there is no response content to send.
Card 26
Question
Which HTTP status code means the server understood the request but refuses to fulfill it?
Answer
403 Forbidden. Repeating the same request with the same credentials should not be automatic.
Card 27
Question
Which HTTP status code has the registered reason phrase “Moved Permanently”?
Answer
301 Moved Permanently. Future references should use the new permanent URI.
Card 28
Question
Which HTTP status code means the server is temporarily unable to handle the request?
Answer
503 Service Unavailable. Temporary overload or maintenance are typical reasons.
Card 29
Question
Which HTTP status code has the registered reason phrase “Bad Request”?
Answer
400 Bad Request. The server perceives a client-side problem that prevents or discourages processing.
Card 30
Question
Which HTTP status code means a gateway or proxy received an invalid inbound response?
Answer
502 Bad Gateway. The upstream response arrived, but it was invalid.
Card 31
Question
Which HTTP status code has the registered reason phrase “Accepted”?
Answer
202 Accepted. Processing has been accepted but is not complete.
Card 32
Question
Which HTTP status code tells a conditional GET or HEAD to use a stored representation?
Answer
304 Not Modified. The request condition evaluated false, so the stored representation remains valid for this response.
Card 33
Question
What does HTTP status code 100 mean?
Answer
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.Card 34
Question
What does HTTP status code 206 mean?
Answer
Partial Content. The server is successfully fulfilling a range request by transferring one or more parts of the selected representation.
Card 35
Question
What does HTTP status code 307 mean?
Answer
Temporary Redirect. The resource is temporarily at another URI, and an automatic redirect must preserve the request method.
Card 36
Question
What does HTTP status code 409 mean?
Answer
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.
Card 37
Question
What does HTTP status code 504 mean?
Answer
Gateway Timeout. A gateway or proxy did not receive a timely response from an upstream server needed to complete the request.
Card 38
Question
What does HTTP status code 101 mean?
Answer
Switching Protocols. The server accepts the client’s
Upgraderequest and names the protocol that will be used after this response.Card 39
Question
Which HTTP status code means a range request succeeded with only part of the representation?
Answer
206 Partial Content. The response carries one or more requested ranges.
Card 40
Question
Which temporary redirect status code requires method preservation?
Answer
307 Temporary Redirect. An automatic redirect must not change the request method.
Card 41
Question
Which HTTP status code means a request conflicts with the target resource’s current state?
Answer
409 Conflict. The client may be able to resolve the state conflict and try again.
Card 42
Question
Which HTTP status code means a gateway timed out waiting for an upstream server?
Answer
504 Gateway Timeout. The upstream response did not arrive in time.
Card 43
Question
What does HTTP status code 102 mean?
Answer
Processing. This registered interim response says the server accepted the complete request but has not finished processing it; a final response still follows.
Card 44
Question
What does HTTP status code 203 mean?
Answer
Non-Authoritative Information. The request succeeded, but a transforming proxy modified the enclosed content from the origin server’s 200 response.
Card 45
Question
What does HTTP status code 308 mean?
Answer
Permanent Redirect. The resource has a new permanent URI, and an automatic redirect must preserve the request method.
Card 46
Question
What does HTTP status code 410 mean?
Answer
Gone. Access to the target resource is no longer available at the origin server, and the condition is likely permanent.
Card 47
Question
What does HTTP status code 501 mean?
Answer
Not Implemented. The server does not support functionality required to fulfill the request, such as an unrecognized method it cannot support for any resource.
Card 48
Question
What does HTTP status code 103 mean?
Answer
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.
Card 49
Question
What does HTTP status code 205 mean?
Answer
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.
Card 50
Question
Which permanent redirect status code requires method preservation?
Answer
308 Permanent Redirect. Future requests should use the new URI without changing the method during automatic redirection.
Card 51
Question
Which HTTP status code says a resource is no longer available and is likely gone permanently?
Answer
410 Gone. Use 404 when the server does not know whether the absence is permanent.
102 cards
HTTP Status Code Flashcards: Meanings, Classes & Use Cases
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Card 52
Question
Which HTTP status code means the required server functionality is unsupported?
Answer
501 Not Implemented. It applies when the server cannot support the functionality needed to fulfill the request.
Card 53
Question
What does HTTP status code 207 mean?
Answer
Multi-Status. The response reports status for multiple independent operations, as defined for WebDAV.
Card 54
Question
What does HTTP status code 300 mean?
Answer
Multiple Choices. The target has more than one representation, and the response provides alternatives so the user or user agent can choose.
Card 55
Question
What does HTTP status code 405 mean?
Answer
Method Not Allowed. The origin server knows the request method, but the target resource does not support it. The response includes an
Allowfield.Card 56
Question
What does HTTP status code 505 mean?
Answer
HTTP Version Not Supported. The server does not support, or refuses to support, the major HTTP version used in the request.
Card 57
Question
What does HTTP status code 208 mean?
Answer
Already Reported. Inside a WebDAV multistatus response, it avoids repeatedly enumerating descendants of another binding to the same collection.
Card 58
Question
What does HTTP status code 303 mean?
Answer
See Other. The
LocationURI identifies a different resource that can provide an indirect response; the user agent retrieves it with GET or HEAD.Card 59
Question
What does HTTP status code 406 mean?
Answer
Not Acceptable. The target has no current representation acceptable under the request’s proactive negotiation fields, and the server will not send a default.
Card 60
Question
What does HTTP status code 506 mean?
Answer
Variant Also Negotiates. The server has a transparent content-negotiation configuration error: the chosen variant is itself configured to negotiate.
Card 61
Question
What does HTTP status code 226 mean?
Answer
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.Card 62
Question
What does HTTP status code 305 mean?
Answer
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.
Card 63
Question
What does HTTP status code 407 mean?
Answer
Proxy Authentication Required. The client must authenticate to a proxy for this request. The proxy sends a
Proxy-Authenticatechallenge.Card 64
Question
What does HTTP status code 507 mean?
Answer
Insufficient Storage. The server cannot store the representation needed to complete the method. WebDAV defines this as a temporary condition.
Card 65
Question
What does HTTP status code 408 mean?
Answer
Request Timeout. The server did not receive a complete request message within the time it was prepared to wait.
Card 66
Question
What does HTTP status code 508 mean?
Answer
Loop Detected. The server terminated a WebDAV operation after finding an infinite loop while processing a
Depth: infinityrequest.Card 67
Question
What does HTTP status code 412 mean?
Answer
Precondition Failed. One or more conditions in the request fields evaluated to false against the current resource state.
Card 68
Question
What does HTTP status code 511 mean?
Answer
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.
Card 69
Question
What does HTTP status code 413 mean?
Answer
Content Too Large. The server refuses to process the request because its content is larger than the server is willing or able to process.
Card 70
Question
What does HTTP status code 411 mean?
Answer
Length Required. The server refuses the request without a defined
Content-Length; the client can retry with a valid value.Card 71
Question
Which HTTP status code means a request precondition evaluated to false?
Answer
412 Precondition Failed. The method is not applied when the stated condition does not match the resource’s current state.
Card 72
Question
Which HTTP status code asks the client to authenticate for network access rather than to the origin server?
Answer
511 Network Authentication Required. It is designed for intercepting network proxies such as captive portals.
Card 73
Question
What does HTTP status code 414 mean?
Answer
URI Too Long. The server refuses the request because the target URI is longer than it is willing to interpret.
Card 74
Question
Which HTTP status code means the request content is too large to process?
Answer
413 Content Too Large. The refusal is about the size of the request content, not the URI or request headers.
Card 75
Question
What does HTTP status code 415 mean?
Answer
Unsupported Media Type. The origin server refuses the request because its content format is unsupported for this method on the target resource.
Card 76
Question
What does HTTP status code 416 mean?
Answer
Range Not Satisfiable. The requested ranges were rejected because none can be satisfied or because the request contains too many small or overlapping ranges.
Card 77
Question
What does HTTP status code 422 mean?
Answer
Unprocessable Content. The server understands the content type and the syntax is correct, but it cannot process the contained instructions.
Card 78
Question
What does HTTP status code 417 mean?
Answer
Expectation Failed. At least one inbound server could not meet the expectation stated in the request’s
Expectfield.Card 79
Question
Which HTTP status code means the request content format is unsupported for the target method?
Answer
415 Unsupported Media Type. The issue can come from
Content-Type,Content-Encoding, or inspecting the data itself.Card 80
Question
What does HTTP status code 421 mean?
Answer
Misdirected Request. The request reached a server that cannot or will not produce an authoritative response for that target URI on the received connection.
Card 81
Question
What does HTTP status code 423 mean?
Answer
Locked. In WebDAV, the source or destination resource for the method is locked.
Card 82
Question
Which HTTP status code means syntactically correct content cannot be processed?
Answer
422 Unprocessable Content. The content type is understood and the syntax is valid, but the contained instructions cannot be processed.
Card 83
Question
What does HTTP status code 424 mean?
Answer
Failed Dependency. The requested action depended on another action, and that other action failed.
Card 84
Question
What does HTTP status code 425 mean?
Answer
Too Early. The server is unwilling to risk processing a request that might be replayed, such as a request sent in TLS early data.
Card 85
Question
What does HTTP status code 429 mean?
Answer
Too Many Requests. The user sent too many requests in a given time. The response may include
Retry-After.Card 86
Question
What does HTTP status code 426 mean?
Answer
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.Card 87
Question
What does HTTP status code 428 mean?
Answer
Precondition Required. The origin server requires a conditional request, commonly to prevent a lost update when resource state changes between reading and writing.
Card 88
Question
What does HTTP status code 431 mean?
Answer
Request Header Fields Too Large. The server refuses to process the request because all request headers together, or one particular header, are too large.
Card 89
Question
Which HTTP status code is registered for rate limiting?
Answer
429 Too Many Requests. It indicates too many requests in a given amount of time.
Card 90
Question
What does HTTP status code 451 mean?
Answer
Unavailable For Legal Reasons. Access is denied because of a legal demand. The code does not establish whether the resource exists.
Card 91
Question
How do HTTP 401 and 403 differ?
Answer
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.
Card 92
Question
How do HTTP 301, 302, 307, and 308 differ?
Answer
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.
Card 93
Question
How do HTTP 409 and 422 differ?
Answer
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.
Card 94
Question
Which HTTP status code means access is denied because of a legal demand?
Answer
451 Unavailable For Legal Reasons. The response can explain the legal demand and who it affects.
Card 95
Question
How do HTTP 404 and 410 differ?
Answer
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.
Card 96
Question
How do HTTP 202 and 204 differ?
Answer
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.
Card 97
Question
How do HTTP 502 and 504 differ?
Answer
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.
Card 98
Question
What does HTTP status code 104 mean, and what is its registry status?
Answer
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.
Card 99
Question
What does HTTP status code 402 mean?
Answer
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.
Card 100
Question
What is the current registry status of HTTP 306?
Answer
Unused and reserved. RFC 9110 says 306 was defined previously, is no longer used, and remains reserved. It is not an ordinary redirect code.
Card 101
Question
What is the current registry status of HTTP 418?
Answer
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.
Card 102
Question
What is the current registry status of HTTP 510?
Answer
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 cards
HTTP Status Code Flashcards: Meanings, Classes & Use Cases
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