List of HTTP status codes in PHP

http-status-codes.php

<?php

/**
 * Content from http://en.wikipedia.org/wiki/List_of_HTTP_status_codes
 *
 * You may also want a list of unofficial codes:
 *
 *  103 => 'Checkpoint',
 *  218 => 'This is fine', // Apache Web Server
 *  419 => 'Page Expired', // Laravel Framework
 *  420 => 'Method Failure', // Spring Framework
 *  420 => 'Enhance Your Calm', // Twitter
 *  430 => 'Request Header Fields Too Large', // Shopify
 *  450 => 'Blocked by Windows Parental Controls', // Microsoft
 *  498 => 'Invalid Token', // Esri
 *  499 => 'Token Required', // Esri
 *  509 => 'Bandwidth Limit Exceeded', // Apache Web Server/cPanel
 *  526 => 'Invalid SSL Certificate', // Cloudflare and Cloud Foundry's gorouter
 *  529 => 'Site is overloaded', // Qualys in the SSLLabs
 *  530 => 'Site is frozen', // Pantheon web platform
 *  598 => 'Network read timeout error', // Informal convention
 *  440 => 'Login Time-out', // IIS
 *  449 => 'Retry With', // IIS
 *  451 => 'Redirect', // IIS
 *  444 => 'No Response', // nginx
 *  494 => 'Request header too large', // nginx
 *  495 => 'SSL Certificate Error', // nginx
 *  496 => 'SSL Certificate Required', // nginx
 *  497 => 'HTTP Request Sent to HTTPS Port', // nginx
 *  499 => 'Client Closed Request', // nginx
 *  520 => 'Web Server Returned an Unknown Error', // Cloudflare
 *  521 => 'Web Server Is Down', // Cloudflare
 *  522 => 'Connection Timed Out', // Cloudflare
 *  523 => 'Origin Is Unreachable', // Cloudflare
 *  524 => 'A Timeout Occurred', // Cloudflare
 *  525 => 'SSL Handshake Failed', // Cloudflare
 *  526 => 'Invalid SSL Certificate', // Cloudflare
 *  527 => 'Railgun Error', // Cloudflare
 */
return [
    100 => 'Continue',
    101 => 'Switching Protocols',
    102 => 'Processing', // WebDAV; RFC 2518
    103 => 'Early Hints', // RFC 8297
    200 => 'OK',
    201 => 'Created',
    202 => 'Accepted',
    203 => 'Non-Authoritative Information', // since HTTP/1.1
    204 => 'No Content',
    205 => 'Reset Content',
    206 => 'Partial Content', // RFC 7233
    207 => 'Multi-Status', // WebDAV; RFC 4918
    208 => 'Already Reported', // WebDAV; RFC 5842
    226 => 'IM Used', // RFC 3229
    300 => 'Multiple Choices',
    301 => 'Moved Permanently',
    302 => 'Found', // Previously "Moved temporarily"
    303 => 'See Other', // since HTTP/1.1
    304 => 'Not Modified', // RFC 7232
    305 => 'Use Proxy', // since HTTP/1.1
    306 => 'Switch Proxy',
    307 => 'Temporary Redirect', // since HTTP/1.1
    308 => 'Permanent Redirect', // RFC 7538
    400 => 'Bad Request',
    401 => 'Unauthorized', // RFC 7235
    402 => 'Payment Required',
    403 => 'Forbidden',
    404 => 'Not Found',
    405 => 'Method Not Allowed',
    406 => 'Not Acceptable',
    407 => 'Proxy Authentication Required', // RFC 7235
    408 => 'Request Timeout',
    409 => 'Conflict',
    410 => 'Gone',
    411 => 'Length Required',
    412 => 'Precondition Failed', // RFC 7232
    413 => 'Payload Too Large', // RFC 7231
    414 => 'URI Too Long', // RFC 7231
    415 => 'Unsupported Media Type', // RFC 7231
    416 => 'Range Not Satisfiable', // RFC 7233
    417 => 'Expectation Failed',
    418 => 'I\'m a teapot', // RFC 2324, RFC 7168
    421 => 'Misdirected Request', // RFC 7540
    422 => 'Unprocessable Entity', // WebDAV; RFC 4918
    423 => 'Locked', // WebDAV; RFC 4918
    424 => 'Failed Dependency', // WebDAV; RFC 4918
    425 => 'Too Early', // RFC 8470
    426 => 'Upgrade Required',
    428 => 'Precondition Required', // RFC 6585
    429 => 'Too Many Requests', // RFC 6585
    431 => 'Request Header Fields Too Large', // RFC 6585
    451 => 'Unavailable For Legal Reasons', // RFC 7725
    500 => 'Internal Server Error',
    501 => 'Not Implemented',
    502 => 'Bad Gateway',
    503 => 'Service Unavailable',
    504 => 'Gateway Timeout',
    505 => 'HTTP Version Not Supported',
    506 => 'Variant Also Negotiates', // RFC 2295
    507 => 'Insufficient Storage', // WebDAV; RFC 4918
    508 => 'Loop Detected', // WebDAV; RFC 5842
    510 => 'Not Extended', // RFC 2774
    511 => 'Network Authentication Required', // RFC 6585
];

@GabrieleMartini the Backslash was dropped by GitHub, but maybe a developer should be able to fix that ;-)

just a complete codes list