响应码 431 Request Header Fields Too Large 表示由于请求中的首部字段的值过大，服务器拒绝接受客户端的请求。客户端可以在缩减首部字段的体积后再次发送请求。
该响应码可以用于首部总体体积过大的情况，也可以用于单个首部体积过大的情况。
这种错误不应该出现于经过良好测试的投入使用的系统当中，而是更多出现于测试新系统的时候
431 Request Header Fields Too Large
| Specification | Title |
|---|---|
| RFC 6585, section 5: 431 Request Header Fields Too Large | Additional HTTP Status Codes |
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AcceptAccept-CharsetAccept-EncodingAccept-LanguageAccept-RangesAccess-Control-Allow-CredentialsAccess-Control-Allow-HeadersAccess-Control-Allow-MethodsAccess-Control-Allow-OriginAccess-Control-Expose-HeadersAccess-Control-Max-AgeAccess-Control-Request-HeadersAccess-Control-Request-MethodAgeAllowAuthorizationCache-ControlConnectionContent-DispositionContent-EncodingContent-LanguageContent-LengthContent-LocationContent-RangeContent-Security-PolicyContent-Security-Policy-Report-Only [我来译!]Content-TypeCookieCookie2DNTDateETagExpectExpiresForwardedFromHostIf-MatchIf-Modified-SinceIf-None-MatchIf-RangeIf-Unmodified-SinceKeep-AliveLarge-Allocation [我来译!]Last-ModifiedLocationOriginPragmaProxy-AuthenticateProxy-AuthorizationPublic-Key-PinsPublic-Key-Pins-Report-Only [我来译!]RangeRefererReferrer-PolicyRetry-AfterServerSet-CookieSet-Cookie2SourceMap [我来译!]HTTP Strict Transport SecurityTETk [我来译!]TrailerTransfer-EncodingUpgrade-Insecure-RequestsUser-AgentVaryViaWWW-AuthenticateWarningX-Content-Type-OptionsDNS 预读取X-Forwarded-ForX-Forwarded-HostX-Forwarded-ProtoX-Frame-Options 响应头X-XSS-Protection100 Continue101 Switching Protocol200 OK201 Created202 Accepted203 Non-Authoritative Information204 No Content205 Reset Content206 Partial Content300 Multiple Choices301 Moved Permanently302 Found303 See Other304 Not Modified307 Temporary Redirect308 Permanent Redirect400 Bad Request401 Unauthorized403 Forbidden404 Not Found405 Method Not Allowed406 Not Acceptable407 Proxy Authentication Required408 Request Timeout409 Conflict410 Gone411 Length Required412 Precondition Failed（先决条件失败）413 Payload Too Large414 URI Too Long [我来译!]415 Unsupported Media Type [我来译!]416 Range Not Satisfiable417 Expectation Failed426 Upgrade Required [我来译!]428 Precondition Required429 Too Many Requests431 Request Header Fields Too Large [我来译!]451 Unavailable For Legal Reasons [我来译!]500 内部服务器错误501 Not Implemented502 Bad Gateway [我来译!]503 Service Unavailable [我来译!]504 Gateway Timeout [我来译!]505 HTTP Version Not Supported [我来译!]511 Network Authentication Required [我来译!]CSP: base-uri [我来译!]CSP: block-all-mixed-content [我来译!]CSP: child-src [我来译!]CSP: connect-src [我来译!]CSP: default-src [我来译!]CSP: font-src [我来译!]CSP: form-action [我来译!]CSP: frame-ancestors [我来译!]CSP: frame-src [我来译!]CSP: img-src [我来译!]CSP: manifest-src [我来译!]CSP: media-src [我来译!]CSP: object-src [我来译!]CSP: plugin-types [我来译!]CSP: referrer [我来译!]CSP: report-uri [我来译!]CSP: require-sri-for [我来译!]CSP: sandbox [我来译!]CSP: script-src [我来译!]CSP: style-src [我来译!]CSP: upgrade-insecure-requests [我来译!]CSP: worker-src [我来译!]