ler general field value indicates that the given set of header fields is present in the trailer of a message encoded with [ chunked transfer coding ](/wiki/Chunked_transfer_coding "Chunked transfer coding") .  |  ` Trailer: Max-Forwards ` |  Permanent  |  [ RFC ](/wiki/RFC_\(identifier\) "RFC \(identifier\)") [ 9110 ](https://datatracker.ietf.org/doc/html/rfc9110)  
Transfer-Encoding  |  The form of encoding used to safely transfer the entity to the user. [ Currently defined methods ](https://www.iana.org/assignments/http-parameters) are: [ chunked ](/wiki/Chunked_transfer_encoding "Chunked transfer encoding") , compress, deflate, gzip, identity.  Must not be used with HTTP/2.  [14]  |  ` Transfer-Encoding: chunked ` |  Permanent  |  [ RFC ](/wiki/RFC_\(identifier\) "RFC \(identifier\)") [ 9110 ](https://datatracker.ietf.org/doc/html/rfc9110)  
[ User-Agent ](/wiki/User-Agent "User-Agent") |  The [ user agent string ](/wiki/User_agent_string "User agent string") of the user agent.  |  ` User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20100101 Firefox/12.0 ` |  Permanent  |  [ RFC ](/wiki/RFC_\(identifier\) "RFC \(identifier\)") [ 9110 ](https://datatracker.ietf.org/doc/html/rfc9110)  
[ Upgrade ](/wiki/Upgrade_header "Upgrade header") |  Ask the server to upgrade to another protocol.  Must not be used in HTTP/2.  [14]  |  ` Upgrade: h2c, HTTPS/1.3, IRC/6.9, RTA/x11, websocket ` |  Permanent  |  [ RFC ](/wiki/RFC_\(identifier\) "RFC \(identifier\)") [ 9110 ](https://datatracker.ietf.org/doc/html/rfc9110)  
Via  |  Informs the server of proxies through which the request was sent.  |  ` Via: 1.0 fred, 1.1 example.com (Apache/1.1) ` |  Permanent  |  [ RFC ](/wiki/RFC_\(identifier\) "RFC \(identifier\)") [ 9110 ](https://datatracker.ietf.org/doc/html/rfc9110)  
Warning  |  A general warning about possible problems with the entity body.  |  ` Warning: 199 Miscellaneous warning ` |  Obsolete  [21]  |  [ RFC ](/wiki/RFC_\(identifier\) "RFC \(identifier\)") [ 7234 ](https://datatracker.ietf.org/doc/html/rfc7234) , [ 9111 ](https://datatracker.ietf.org/doc/html/rfc9111)  
  
###  Common non-standard request fields  [  [ edit
](/w/index.php?title=List_of_HTTP_header_fields&action=edit&section=7 "Edit
section: Common non-standard request fields") ]

Field name  |  Description  |  Example   
---|---|---  
Upgrade-Insecure-Requests  [22]  |  Tells a server which (presumably in the middle of a HTTP -> HTTPS migration) hosts mixed content that the client would prefer redirection to HTTPS and can handle ` Content-Security-Policy: upgrade-insecure-requests ` Must not be used with HTTP/2  [14]  |  ` Upgrade-Insecure-Requests: 1 `  
X-Requested-With  |  Mainly used to identify [ Ajax ](/wiki/Ajax_\(programming\) "Ajax \(programming\)") requests (most [ JavaScript frameworks ](/wiki/JavaScript_framework "JavaScript framework") send this field with value of ` XMLHttpRequest ` ); also identifies Android apps using WebView  [23]  |  ` X-Requested-With: XMLHttpRequest `  
[ DNT ](/wiki/Do_Not_Track "Do Not Track") [24]  |  Requests a web application to disable their tracking of a user. This is Mozilla's version of the X-Do-Not-Track header field (since [ Firefox 4.0 ](/wiki/Mozilla_Firefox_4 "Mozilla Firefox 4") Beta 11). [ Safari ](/wiki/Safari_\(web_browser\) "Safari \(web browser\)") and [ IE9 ](/wiki/Internet_Explorer_9 "Internet Explorer 9") also have support for this field.  [25]  On March 7, 2011, a draft proposal was submitted to IETF.  [26]  The [ W3C ](/wiki/World_Wide_Web_Consortium "World Wide Web Consortium") Tracking Protection Working Group is producing a specification.  [27]  |  ` DNT: 1 ` (Do Not Track Enabled)  ` DNT: 0 ` (Do Not Track Disabled)   
[ X-Forwarded-For ](/wiki/X-Forwarded-For "X-Forwarded-For") [28]  |  A [ _de facto_ standard ](/wiki/De_facto_standard "De facto standard") for identifying the originating IP address of a client connecting to a web server through an HTTP proxy or load balancer. Superseded by _F