HTTP status codes:

Here is the list of all the valid HTTP - status codes, and the corresponding phrases, that PHP scripting language can generate when using the $http_response_code parameter in the header() function.
The invalid codes (for example: 199) generate a 500 Internal Server Error response.

To send a specific HTTP status code, the prototype of the header() function is:
void header(string $string, bool $replace, int $http_response_code)

The 3 parameters are:

string $string:
Several cases:

an empty string: ''

we have to AVOID this case, as then the function does NOT work!

a NOT empty string, which does NOT contain any colon ':' character:

the more usual case, to send the desired status code and phrase

a NOT empty string, which contains a colon ':' character inside:

a useful case, to send the desired status code and phrase AND a response header
(see examples below)
bool $replace: always TRUE
int $http_response_code: an integer, the desired status code, in the range: from 100 to 510

Examples of use:

The string parameter does not contain any colon character: /* The server will ouput: * the response status "HTTP/1.1 204 No Content" */ header('x', TRUE, 204);
The string parameter contains a response header, of which the syntax is: <string header-name><char colon><char space><string header-value>: /* The server will ouput: * the response status "HTTP/1.1 405 Method Not Allowed" * and the response header "Allow: GET, HEAD" */ header('Allow: GET, HEAD', TRUE, 405);

List of status codes and phrases generated by PHP:

›100 Continue
›101 Switching Protocols
›102 Processing
›103 Early Hints

›200 OK
›201 Created
›202 Accepted
›203 Non-Authoritative Information
›204 No Content
›205 Reset Content
›206 Partial Content
›207 Multi-Status
›208 Already Reported

›226 IM Used

›300 Multiple Choices
›301 Moved Permanently
›302 Found
›303 See Other
›304 Not Modified
›305 Use Proxy

›307 Temporary Redirect
›308 Permanent Redirect

›400 Bad Request
›401 Unauthorized
›402 Payment Required
›403 Forbidden
›404 Not Found
›405 Method Not Allowed
›406 Not Acceptable
›407 Proxy Authentication Required
›408 Request Timeout
›409 Conflict
›410 Gone
›411 Length Required
›412 Precondition Failed
›413 Request Entity Too Large
›414 Request-URI Too Long
›415 Unsupported Media Type
›416 Requested Range Not Satisfiable
›417 Expectation Failed

›421 Misdirected Request
›422 Unprocessable Entity
›423 Locked
›424 Failed Dependency

›426 Upgrade Required

›428 Precondition Required
›429 Too Many Requests

›431 Request Header Fields Too Large

›451 Unavailable For Legal Reasons

›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
›507 Insufficient Storage
›508 Loop Detected

›510 Not Extended
›511 Network Authentication Required

Get the list in these other formats:

Format	Description
Text	code[HT]phrase[LF] ...
CSV	code,"phrase"[LF] ...
XML	<?xml version="1.0" encoding="UTF-8"?> <http-status-codes> <status> <code>code</code> <phrase>phrase</phrase> </status> ... </http-status-codes>
PHP	$a_http_status_codes = array( code => 'phrase', ... );
Javascript	var oHttpStatusCodes = { code: 'phrase', ... };
JSON	{"oHttpStatusCodes": { "code": "phrase", ... }}
MySQL	INSERT INTO `http_status_codes` (`code`, `phrase`) VALUES (code, 'phrase'), ...;

Hypertext Transfer Protocol:

Resource	Description
RFC 2616 (HTML)	HTTP/1.1
RFC 2616 (Text)	HTTP/1.1
RFC 4918 (HTML)	HTTP Extensions for Web Distributed Authoring and Versioning
RFC 4918 (Text)