Tk header

{{non-standard_header}}
[!NOTE]
The DNT (Do Not Track) specification has been discontinued. See {{domxref("Navigator.doNotTrack")}} for more information.
An alternative is Global Privacy Control, which is communicated to servers using the {{HTTPHeader("Sec-GPC")}} header, and accessible to clients from {{domxref("navigator.globalPrivacyControl")}}.
The HTTP 
Tk {{Glossary("response header")}} indicates the tracking status that applied to the corresponding request.
  
    
      
Header type
      
{{Glossary("Response header")}}
    
  
Syntax
Tk: !  (under construction)
Tk: ?  (dynamic)
Tk: G  (gateway or multiple parties)
Tk: N  (not tracking)
Tk: T  (tracking)
Tk: C  (tracking with consent)
Tk: P  (potential consent)
Tk: D  (disregarding DNT)
Tk: U  (updated)
Directives
!
: Under construction. The origin server is currently testing its communication of
tracking status.
?
: Dynamic. The origin server needs more information to determine tracking status.
G
: Gateway or multiple parties. The server is acting as a gateway to an exchange
involving multiple parties.
N
: Not tracking.
T
: Tracking.
C
: Tracking with consent. The origin server believes it has received prior consent for
tracking this user, user agent, or device.
P
: Potential consent. The origin server does not know, in real-time, whether it has
received prior consent for tracking this user, user agent, or device, but promises not
to use or share any 
DNT:1 data until such consent has been determined,
and further promises to delete or permanently de-identify within 48 hours any
DNT:1 data received for which such consent has not been received.
D
: Disregarding DNT. The origin server is unable or unwilling to respect a tracking
preference received from the requesting user agent.
U
: Updated. The request resulted in a potential change to the tracking status
applicable to this user, user agent, or device.
Examples
A 
Tk header for a resource that claims not to be tracking would look like:
Tk: N
Specifications
{{specifications}}
Browser compatibility
This response header doesn't trigger any browser behavior, so browser compatibility is irrelevant.
See also
{{HTTPHeader("DNT")}} header
{{domxref("Navigator.doNotTrack")}}
Do Not Track on Wikipedia
What Does the "Track" in "Do Not Track" Mean? – EFF
DNT on Electronic Frontier Foundation
GPC - Global Privacy Control
Enabling GPC in Firefox