Plan-execute-verify on Twelve HTTP status codes, by the book

All twelve answers come from RFC 9110 (HTTP Semantics, June 2022), which I opened at https://www.rfc-editor.org/rfc/rfc9110.html. Its header has no "Obsoleted by" line, and I didn't search for a newer RFC.

• Reason phrases and section numbers: I read each defining section directly. The phrases are the ones the current text gives. For example, 413 is "Content Too Large" and 422 is "Unprocessable Content", not the older RFC 7231 names.

• Heuristic cacheability, confirmed two ways:

  • Section 15.1 lists the heuristically cacheable codes as "200, 203, 204, 206, 300, 301, 308, 404, 405, 410, 414, and 501" and says "all other status codes are not heuristically cacheable".
  • The sections for 203, 206, 308, 405, 410, 414 and 501 each say "A NNN response is heuristically cacheable".
  • So 303, 307, 413, 421 and 422 are not heuristically cacheable. Their sections say nothing about it, and they aren't in the 15.1 list.
• One wording difference: the 206 section says "unless otherwise indicated by explicit cache controls", while the other sections also say "by the method definition". This doesn't change the answer.
• Sources: all twelve quotes come from the one page above. I found no disagreement between sources.

{"answers":[{"code":"203","reason":"Non-Authoritative Information","section":"15.3.4","heuristicallyCacheable":true,"quote":"A 203 response is heuristically cacheable; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of [CACHING]).","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"206","reason":"Partial Content","section":"15.3.7","heuristicallyCacheable":true,"quote":"The 206 (Partial Content) status code indicates that the server is successfully fulfilling a range request for the target resource by transferring one or more parts of the selected representation.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"303","reason":"See Other","section":"15.4.4","heuristicallyCacheable":false,"quote":"This status code is applicable to any HTTP method.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"307","reason":"Temporary Redirect","section":"15.4.8","heuristicallyCacheable":false,"quote":"Since the redirection can change over time, the client ought to continue using the original target URI for future requests.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"308","reason":"Permanent Redirect","section":"15.4.9","heuristicallyCacheable":true,"quote":"A 308 response is heuristically cacheable; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of [CACHING]).","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"405","reason":"Method Not Allowed","section":"15.5.6","heuristicallyCacheable":true,"quote":"The origin server MUST generate an Allow header field in a 405 response containing a list of the target resource's currently supported methods.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"410","reason":"Gone","section":"15.5.11","heuristicallyCacheable":true,"quote":"A 410 response is heuristically cacheable; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of [CACHING]).","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"413","reason":"Content Too Large","section":"15.5.14","heuristicallyCacheable":false,"quote":"If the condition is temporary, the server SHOULD generate a Retry-After header field to indicate that it is temporary and after what time the client MAY try again.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"414","reason":"URI Too Long","section":"15.5.15","heuristicallyCacheable":true,"quote":"A 414 response is heuristically cacheable; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of [CACHING]).","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"421","reason":"Misdirected Request","section":"15.5.20","heuristicallyCacheable":false,"quote":"A proxy MUST NOT generate a 421 response.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"422","reason":"Unprocessable Content","section":"15.5.21","heuristicallyCacheable":false,"quote":"For example, this status code can be sent if an XML request content contains well-formed (i.e., syntactically correct), but semantically erroneous XML instructions.","url":"https://www.rfc-editor.org/rfc/rfc9110.html"},{"code":"501","reason":"Not Implemented","section":"15.6.2","heuristicallyCacheable":true,"quote":"A 501 response is heuristically cacheable; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of [CACHING]).","url":"https://www.rfc-editor.org/rfc/rfc9110.html"}]}