IIS Server Variables

IIS Server Variables provide information about the server, the connection with the client, and the current request on the connection. Additionally, inbound URL rewrite rules can be used to set custom server variables.

Note

Not all server variables listed in this document are available in versions of IIS prior to IIS 8.5.

Server Variable	Description
ALL_HTTP	All HTTP headers sent by the client. The headers are prefixed by with HTTP_ and capitalized. For example, HTTP_ACCEPT_ENCODING:gzip, deflate, br
ALL_RAW	All HTTP headers sent by the client in raw form. For example, Accept-Encoding: gzip, deflate, br
APPL_MD_PATH	The metabase path of the application.
APPL_PHYSICAL_PATH	The physical path of the application.
APP_POOL_CONFIG	The physical path of the temporary IIS application pool configuration.
APP_POOL_ID	The name of the application pool that is running the IIS worker process handling the request.
AUTH_PASSWORD	The password provided by the client to authenticate using Basic Authentication.
AUTH_TYPE	The authentication method that the server uses to validate users. It does not mean that the user was authenticated if AUTH_TYPE contains a value and the authentication scheme is not Basic or integrated Windows authentication. The server allows authentication schemes it does not natively support because an ISAPI filter may be able to handle that particular scheme.
AUTH_USER	The name of the user as it is derived from the authorization header sent by the client, before the user name is mapped to a Windows account. This variable is no different from REMOTE_USER. If you have an authentication filter installed on your Web server that maps incoming users to accounts, use LOGON_USER to view the mapped user name.
CACHE_URL	For use in ISAPI applications only. Returns the unambiguous name for the current URL. It is necessary to use the Unicode version of this variable in conjunction with the kernel mode cache invalidation function to evict entries placed in the cache by HSE_REQ_VECTOR_SEND.
CERT_COOKIE	Unique ID for the client certificate, returned as a string. This can be used as a signature for the whole client certificate.
CERT_FLAGS	bit0 is set to 1 if the client certificate is present. bit0 is set to 1 if the certification authority of the client certificate is invalid (that is, it is not in the list of recognized certification authorities on the server). If bit 1 of CERT_FLAGS is set to 1, indicating that the certificate is invalid, IIS version 4.0 and later will reject the certificate. Earlier versions of IIS will not reject the certificate.
CERT_ISSUER	The issuer field of the client certificate.
CERT_KEYSIZE	The number of bits in the SSL/TLS connection key size.
CERT_SECRETKEYSIZE	The number of bits in the SSL/TLS server private key.
CERT_SERIALNUMBER	Serial number of the client certificate.
CERT_SERVER_ISSUER	The issuer field of the server certificate.
CERT_SERVER_SUBJECT	The subject field of the server certificate.
CERT_SUBJECT	The subject field of the client certificate.
CONTENT_LENGTH	The length of the request body.
CONTENT_TYPE	The MIME type of the request body. Used with queries that have attached information, such as GET, POST, and PUT.
CRYPT_CIPHER_ALG_ID	The cryptographic cipher algorithm used to establish the connection. The hex value of the algorithm is established in the ALG_ID data type. For example, 256-bit AES(CALG_AES_256) will be 6610.
CRYPT_HASH_ALG_ID	The hashing algorithm used for generating Message Authentication Codes (MACs). The hex value of the algorithm is established in the ALG_ID data type. For example, MD5(CALG_MD5) will be 8003.
CRYPT_KEYEXCHANGE_ALG_ID	The key-exchange algorithm used to establish the connection. The hex value of the algorithm is established in the ALG_ID data type. For example, Elliptic curve Diffie-Hellman key exchange algorithm(CALG_ECDH) will be aa05.
CRYPT_PROTOCOL	The cryptographic protocol used to establish the connection. The hex value of the protocol is established in the SecPkgContext_ConnectionInfo structure. For example, TLS 1.2 will be 400.
DOCUMENT_ROOT	The physical path of the directory the IIS Website.
FORWARDED_URL	The forwarded URL.
GATEWAY_INTERFACE	The revision of the CGI specification used by the server. The format is CGI/revision.
HTTPS	Returns ON if the request came in through a secure channel (for example, SSL); or it returns OFF, if the request is for an insecure channel.
HTTPS_KEYSIZE	Number of bits in the SSL/TLS connection key size.
HTTPS_SECRETKEYSIZE	Number of bits in the server certificate private key.
HTTPS_SERVER_ISSUER	Issuer field of the server certificate.
HTTPS_SERVER_SUBJECT	Subject field of the server certificate.
HTTP_METHOD	The method used to make the request.
HTTP_URL	The raw encoded URL. For example, /vdir/default.aspx?querystring
HTTP_VERSION	The name and version of the request protocol (the raw form of SERVER_PROTOCOL).
INSTANCE_ID	The IIS site ID.
INSTANCE_META_PATH	The metabase path for the instance of IIS that responds to the request.
INSTANCE_NAME	The IIS site name.
LOCAL_ADDR	The server address on which the request came in. This is important on computers where there can be multiple IP addresses bound to the computer, and you want to find out which address the request used.
LOGON_USER	The Windows account that the user is impersonating while connected to your Web server. Use REMOTE_USER, UNMAPPED_REMOTE_USER, or AUTH_USER to view the raw user name that is contained in the request header. The only time LOGON_USER holds a different value than these other variables is if you have an authentication filter installed.
MANAGED_PIPELINE_MODE	The managed pipeline mode of the application pool that is running the IIS worker process handling the request.
PATH_INFO	Path information, as given by the client, for example, /vdir/myisapi.dll/zip. If this information comes from a URL, it is decoded by the server before it is passed to the CGI script or ISAPI filter. If the AllowPathInfoForScriptMappings metabase property is set to true (to support exclusive CGI functionality), PATH_INFO will only contain /zip and ISAPI applications such as ASP will break.
PATH_TRANSLATED	The physical path that maps to the virtual path in PATH_INFO, for example, c:\inetpub\wwwroot\vdir\myisapi.dll. This variable is used by IIS during the processing of ISAPI applications. If the AllowPathInfoForScriptMappings metabase property is set to true (to support exclusive CGI functionality), PATH_INFO will only contain /zip and ISAPI applications such as ASP will break.
QUERY_STRING	Query information stored in the string following the question mark (?) in the HTTP request.
REMOTE_ADDR	The IP address of the remote host that is making the request.
REMOTE_HOST	The name of the host that is making the request. If the server does not have this information, it will set REMOTE_ADDR and leave this empty.
REMOTE_PORT	The client port number of the TCP connection.
REMOTE_USER	The name of the user as it is derived from the authorization header sent by the client, before the user name is mapped to a Windows account. If you have an authentication filter installed on your Web server that maps incoming users to accounts, use LOGON_USER to view the mapped user name.
REQUEST_FILENAME	The physical path for the current request.
REQUEST_FLAGS	The Flags of HTTP_REQUEST. For example, the HTTP_REQUEST_FLAG_HTTP2 flag will be set for HTTP/2 requests.
REQUEST_METHOD	The method used to make the request.
REQUEST_URI	The path-absolute part of the URI. For example https://contoso.com:8042/over/there?name=ferret would return /over/there
SCRIPT_FILENAME	The physical path of the current request.
SCRIPT_NAME	A virtual path to the script being executed.
SCRIPT_TRANSLATED	The extended-length path to the requested file (prefixed with \\?\).
SERVER_ADDR	The IP address that the site is bound to.
SERVER_NAME	The server's host name, DNS alias, or IP address as it would appear in self-referencing URLs.
SERVER_PORT	The server port number to which the request was sent.
SERVER_PORT_SECURE	A string that contains either 0 or 1. If the request is being handled on the secure port, then this is 1. Otherwise, it is 0.
SERVER_PROTOCOL	The name and revision of the request information protocol. The format is protocol/revision. (The canonicalized form of HTTP_VERSION.)
SERVER_SOFTWARE	The name and version of the server software that answers the request and runs the gateway. The format is name/version.
UNENCODED_URL	The raw unencoded URL.
UNMAPPED_REMOTE_USER	The name of the user as it is derived from the authorization header sent by the client, before the user name is mapped to a Windows account (same as REMOTE_USER). If you have an authentication filter installed on your Web server that maps incoming users to accounts, use LOGON_USER to view the mapped user name.
URL	The base portion of the URL without any querystring information.