Tracking Preference Expression (DNT)

W3C Working Draft 02 October 2012

This version:
Latest published version:
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Roy T. Fielding, Adobe
David Singer, Apple


This specification defines the technical mechanisms for expressing a tracking preference via the DNT request header field in HTTP, via an HTML DOM property readable by embedded scripts, and via properties accessible to various user agent plug-in or extension APIs. It also defines mechanisms for sites to signal whether and how they honor this preference, both in the form of a machine-readable tracking status resource at a well-known location and via a Tk response header field, and a mechanism for allowing the user to approve site-specific exceptions to DNT as desired.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document is a snapshot of live discussions within the Tracking Protection Working Group. It does not yet capture all of our work. For example, we have issues that are [PENDING REVIEW] with complete text proposals that have not yet made it into this draft. Text in blue boxes presents multiple options the group is considering. Options included in this draft should not be read as limitations on the potential outcome, but rather simply as possible options that are currently under consideration by the working group. Readers may review changes from the previous Working Draft. An issue tracking system is available for recording raised, open, pending review, closed, and postponed issues regarding this document.

This document was published by the Tracking Protection Working Group as a Working Draft. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to public-tracking@w3.org (subscribe, archives). All feedback is welcome.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1. Introduction

The World Wide Web (WWW, or Web) consists of millions of sites interconnected through the use of hypertext. Hypertext provides a simple, page-oriented view of a wide variety of information that can be traversed by selecting links, manipulating controls, and supplying data via forms and search dialogs. A Web page is usually composed of many different information sources beyond the initial resource request, including embedded references to stylesheets, inline images, javascript, and other elements that might be automatically requested as part of the rendering or behavioral processing defined for that page.

Each of the hypertext actions and each of the embedded resource references might refer to any site on the Web, leading to a seamless interaction with the user even though the pages might be composed of information requested from many different and possibly independent Web sites. From the user's perspective, they are simply visiting and interacting with a single brand — the first-party Web property — and all of the technical details and protocol mechanisms that are used to compose a page representing that brand are hidden behind the scenes.

It has become common for Web site owners to collect data regarding the usage of their sites for a variety of purposes, including what led the user to visit their site (referrals), how effective the user experience is within the site (web analytics), and the nature of who is using their site (audience segmentation). In some cases, the data collected is used to dynamically adapt the content (personalization) or the advertising presented to the user (targeted advertising). Data collection can occur both at the first-party site and via third-party providers through the insertion of tracking elements on each page. A survey of these techniques and their privacy implications can be found in [KnowPrivacy].

People have the right to know how data about them will be collected and how it will be used. Empowered with that knowledge, individuals can decide whether to allow their online activities to be tracked and data about them to be collected. Many Internet companies use data gathered about people's online activities to personalize content and target advertising based on their perceived interests. While some people appreciate this personalization of content and ads in certain contexts, others are troubled by what they perceive as an invasion of their privacy. For them, the benefit of personalization is not worth their concerns about allowing entities with whom they have no direct relationship to amass detailed profiles about their activities.

Therefore, users need a mechanism to express their own preference regarding tracking that is both simple to configure and efficient when implemented. In turn, Web sites that are unwilling or unable to offer content without such targeted advertising or data collection need a mechanism to indicate those requirements to the user and allow them (or their user agent) to make an individual choice regarding exceptions.

This specification defines the HTTP request header field DNT for expressing a tracking preference on the Web, a well-known location (URI) for providing a machine-readable tracking status resource that describes a service's DNT compliance, the HTTP response header field Tk for resources to communicate their compliance or non-compliance with the user's expressed preference, and JavaScript APIs for determining DNT status and requesting a user-granted exception.

A companion document, [TRACKING-COMPLIANCE], more precisely defines the terminology of tracking preferences, the scope of its applicability, and the requirements on compliant first-party and third-party participants when an indication of tracking preference is received.

Issue 136: Resolve dependencies of the TPE on the compliance specification

The WG has not come to consensus regarding the definition of tracking and the scope of DNT. As such, a site cannot actually say with any confidence whether or not it is tracking, let alone describe the finer details in a tracking status resource. This issue will be resolved by progress on the TCS document, though its resolution is a necessary prerequisite to understanding and correctly implementing the protocol defined by this document.

2. Notational Conventions

2.1 Requirements

The key words MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this specification are to be interpreted as described in [RFC2119].

2.2 Formal Syntax

This specification uses Augmented Backus-Naur Form [ABNF] to define network protocol syntax and WebIDL [WEBIDL] for defining scripting APIs.

2.3 Terminology

This specification uses the term user agent to refer to any of the various client programs capable of initiating HTTP requests, including, but not limited to, browsers, spiders (web-based robots), command-line tools, native applications, and mobile apps [HTTP11].

The term permitted use is used to indicate a restricted set of conditions under which tracking is allowed in spite of the user's DNT preference.

The term user-granted exception is used when the user has permitted tracking by a given third party, usually in the form of a site-specific exception.

A companion document, [TRACKING-COMPLIANCE], defines many of the terms used here, notably 'party', 'first party', and 'third party'.

3. Determining User Preference

The goal of this protocol is to allow a user to express their personal preference regarding tracking to each server and web application that they communicate with via HTTP, thereby allowing each service to either adjust their behavior to meet the user's expectations or reach a separate agreement with the user to satisfy all parties.

Key to that notion of expression is that it MUST reflect the user's preference, not the choice of some vendor, institution, or network-imposed mechanism outside the user's control. The basic principle is that a tracking preference expression is only transmitted when it reflects a deliberate choice by the user. In the absence of user choice, there is no tracking preference expressed.

A user agent MUST offer users a minimum of two alternative choices for a Do Not Track preference: unset or DNT:1. A user agent MAY offer a third alternative choice: DNT:0.

If the user's choice is DNT:1 or DNT:0, the tracking preference is enabled; otherwise, the tracking preference is not enabled.

A user agent MUST have a default tracking preference of unset (not enabled) unless a specific tracking preference is implied by the decision to use that agent. For example, use of a general-purpose browser would not imply a tracking preference when invoked normally as SuperFred, but might imply a preference if invoked as SuperDoNotTrack or UltraPrivacyFred. Likewise, a user agent extension or add-on MUST NOT alter the tracking preference unless the act of installing and enabling that extension or add-on is an explicit choice by the user for that tracking preference.

We do not specify how tracking preference choices are offered to the user or how the preference is enabled: each implementation is responsible for determining the user experience by which a tracking preference is enabled. For example, a user might select a check-box in their user agent's configuration, install an extension or add-on that is specifically designed to add a tracking preference expression, or make a choice for privacy that then implicitly includes a tracking preference (e.g., Privacy settings: high). The user-agent might ask the user for their preference during startup, perhaps on first use or after an update adds the tracking protection feature. Likewise, a user might install or configure a proxy to add the expression to their own outgoing requests.

Although some controlled network environments, such as public access terminals or managed corporate intranets, might impose restrictions on the use or configuration of installed user agents, such that a user might only have access to user agents with a predetermined preference enabled, the user is at least able to choose whether to make use of those user agents. In contrast, if a user brings their own Web-enabled device to a library or cafe with wireless Internet access, the expectation will be that their chosen user agent and personal preferences regarding Web site behavior will not be altered by the network environment, aside from blanket limitations on what resources can or cannot be accessed through that network. Implementations of HTTP that are not under control of the user MUST NOT generate or modify a tracking preference.

4. Expressing a Tracking Preference

4.1 Expression Format

When a user has enabled a tracking preference, that preference needs to be expressed to all mechanisms that might perform or initiate tracking by third parties, including sites that the user agent communicates with via HTTP, scripts that can extend behavior on pages, and plug-ins or extensions that might be installed and activated for various media types.

When enabled, a tracking preference is expressed as either:

DNT meaning
1 This user prefers not to be tracked on the target site.
0 This user prefers to allow tracking on the target site.

A user agent MUST NOT send a tracking preference expression if a tracking preference is not enabled. This means that no expression is sent for each of the following cases:

In the absence of regulatory, legal, or other requirements, servers MAY interpret the lack of an expressed tracking preference as they find most appropriate for the given user, particularly when considered in light of the user's privacy expectations and cultural circumstances. Likewise, servers might make use of other preference information outside the scope of this protocol, such as site-specific user preferences or third-party registration services, to inform or adjust their behavior when no explicit preference is expressed via this protocol.

4.2 DNT Header Field for HTTP Requests

The DNT header field is hereby defined as the means for expressing a user's tracking preference via HTTP [HTTP11].

DNT-field-name  = "DNT"                          ; case-insensitive
DNT-field-value = ( "0" / "1" ) *DNT-extension   ; case-sensitive
DNT-extension   = %x21 / %x23-2B / %x2D-5B / %x5D-7E
                ; excludes CTL, SP, DQUOTE, comma, backslash

A user agent MUST send the DNT header field on all HTTP requests if (and only if) a tracking preference is enabled. A user agent MUST NOT send the DNT header field if a tracking preference is not enabled.

The DNT field-value sent by a user agent MUST begin with the numeric character "1" (%x31) if a tracking preference is enabled, the preference is for no tracking, and there is not a site-specific exception for the origin server targeted by this request.

The DNT field-value sent by a user agent MUST begin with the numeric character "0" (%x30) if a tracking preference is enabled and the preference is to allow tracking in general or by specific exception for the origin server targeted by this request.

Example 1
GET /something/here HTTP/1.1
Host: example.com
DNT: 1

An HTTP intermediary MUST NOT add, delete, or modify the DNT header field in requests forwarded through that intermediary unless that intermediary has been specifically installed or configured to do so by the user making the requests. For example, an Internet Service Provider MUST NOT inject DNT: 1 on behalf of all of their users who have not expressed a preference.

The remainder of the DNT field-value after the initial character is reserved for future extensions. User agents that do not implement such extensions MUST NOT send DNT-extension characters in the DNT field-value. Servers that do not implement such extensions SHOULD ignore anything beyond the first character.

DNT extensions are to be interpreted as modifiers to the main preference expressed by the first digit, such that the main preference will be obeyed if the recipient does not understand the extension. Hence, a DNT-field-value of "1xyz" can be thought of as do not track, but if you understand the refinements defined by x, y, or z, then adjust my preferences according to those refinements. DNT extensions can only be transmitted when a tracking preference is enabled.

The extension syntax is restricted to visible ASCII characters that can be parsed as a single word in HTTP and safely embedded in a JSON string without further encoding (section 5.5.3 Representation). Since the DNT header field is intended to be sent on every request, when enabled, designers of future extensions ought to use as few extension characters as possible.


This document does not have any implied or specified behavior for the user-agent treatment of cookies when DNT is enabled.

4.3 JavaScript API to Detect Preference

A doNotTrack attribute on the Navigator interface [NAVIGATOR] (e.g., the window.navigator object) is hereby defined as the means for expressing the user's general tracking preference to scripts running within a top-level page. A user agent MUST provide a doNotTrack attribute on the Navigator interface for each top-level page.

partial interface Navigator {
    readonly attribute DOMString doNotTrack;
doNotTrack of type DOMString, readonly
When a tracking preference is enabled, the doNotTrack attribute for each top-level page MUST have the same string value that would be sent in a DNT-field-value (section 4.2 DNT Header Field for HTTP Requests) to an origin server that does not have any corresponding user-granted exceptions. When a tracking preference is not enabled, the doNotTrack attribute for each top-level page MUST have a value of null.

The doNotTrack attribute only provides the user's general tracking preference, independent of any user-granted exceptions or out-of-band consent. A script wishing to determine the specific tracking preference for a given document origin is expected to use the API in section 6.6 Querying a host's exception status.

A user agent MUST provide a doNotTrack attribute value that is consistent with the user's current tracking preference that would be expressed via the DNT header field. However, changes to the user's preference might occur between the time when the APIs are checked and an actual request is made. A server MUST treat the user's most recently received preference as authoritative.

Issue 116: How can we build a JS DOM property which doesn't allow inline JS to receive mixed signals?

[PENDING REVIEW] Updated text in this section.

4.4 Plug-In APIs

User agents often include user-installable component parts, commonly known as plug-ins or browser extensions, that are capable of making their own network requests. From the user's perspective, these components are considered part of the user agent and thus ought to respect the user's configuration of a tracking preference. However, plug-ins do not normally have read access to the browser configuration.


It is unclear whether we need to standardize the plug-in APIs or if we should rely on it being defined per user agent based on general advice here. No plug-in APIs have been proposed yet.

4.5 Tracking Preference Expressed in Other Protocols

A user's tracking preference is intended to apply in general, regardless of the protocols being used for Internet communication. The protocol expressed here is specific to HTTP communication; however, the semantics are not restricted to use in HTTP; the same semantics may be carried by other protocols, either in future revisions of this specification, or in other specifications.

When it is known that the user's preference is for no tracking, compliant services are still required to honor that preference, even if other protocols are used. For example, redirecting to another protocol in order to avoid receipt of the header is not compliant.


The last paragraph may be more appropriate in the compliance document, as it discusses compliance.

5. Communicating a Tracking Status

5.1 Overview

The primary goals of this protocol—expressing the user's preference and adhering to that preference—can be accomplished without any response from the server. However, the protocol also seeks to improve the transparency of tracking behavior by providing a machine-readable means for discovering claims of compliance and determining the current tracking status.

Unfortunately, providing a dynamic indication of tracking compliance on every HTTP response is not feasible, since it would have the effect of disabling caching for the entire Web. Instead, this protocol defines a combination of response mechanisms that allow the information to be communicated without making every response dynamic.

This section explains how a user agent MAY discover an origin server's tracking status for a given resource. It defines a REQUIRED site-wide tracking status resource at a specific well-known location and an OPTIONAL space of request-specific tracking status resources for sites where the tracking status might vary based on data within the request. It also defines a Tk response header field that MAY be sent in any HTTP response, MUST be sent in responses to requests that modify the tracking status, and MAY direct the user to a request-specific tracking status resource applicable to the current request.

5.2 Tracking Status Value

A tracking status value is a short notation for communicating how a designated resource conforms to the tracking protection protocol, as defined by this document and [TRACKING-COMPLIANCE]. There is no form of negative response; i.e., an origin server that does not wish to claim conformance to this protocol would not supply a tracking status resource and would not send a Tk header field in responses.

For a site-wide tracking status resource, the designated resource to which the tracking status applies is any resource on the same origin server. For a Tk response header field, the corresponding request target is the designated resource and remains so for any subsequent request-specific tracking status resource referred to by that field.

All of the tracking status mechanisms use a common format for the tracking status value: a single character from a limited set. The meaning of each allowed character is defined in the following table.

status meaning
N None: The designated resource does not perform tracking of any kind, not even for a permitted use, and does not make use of any data collected from tracking.
1 First party: The designated resource is designed for use within a first-party context and conforms to the requirements on a first party. If the designated resource is operated by an outsourced service provider, the service provider claims that it conforms to the requirements on a third party acting as a first party.
3 Third party: The designated resource is designed for use within a third-party context and conforms to the requirements on a third party.
X Dynamic: The designated resource is designed for use in both first and third-party contexts and dynamically adjusts tracking status accordingly. If X is present in the site-wide tracking status, more information MUST be provided via the Tk response header field when accessing a designated resource. If X is present in the Tk header field, more information will be provided in a request-specific tracking status resource referred to by the status-id. An origin server MUST NOT send X as the tracking status value in the representation of a request-specific tracking status resource.
C Consent: The designated resource believes it has received prior consent for tracking this user, user agent, or device, perhaps via some mechanism not defined by this specification, and that prior consent overrides the tracking preference expressed by this protocol.
U Updated: The request resulted in a potential change to the tracking status applicable to this user, user agent, or device. A user agent that relies on a cached tracking status SHOULD update the cache entry with the current status by making a new request on the applicable tracking status resource. An origin server MUST NOT send U as a tracking status value anywhere other than a Tk header field that is in response to a state-changing request.

For the site-wide tracking status and Tk header field, the tracking status values 1 and 3 indicate how the designated resource is designed to conform, not the nature of the request. Hence, if a user agent is making a request in what appears to be a third-party context and the tracking status value indicates that the designated resource is designed only for first-party conformance, then either the context has been misunderstood (both are actually the same party) or the resource has been referenced incorrectly. For the request-specific tracking status resource, an indication of first or third party as the status value describes how the resource conformed to that specific request, and thus indicates both the nature of the request (as viewed by the origin server) and the applicable set of requirements to which the origin server claims to conform.

The tracking status value is case sensitive, as defined formally by the following ABNF.

tracking-v    = "1"   ; "1" — first-party
              / "3"   ; "3" — third-party
              / %x43  ; "C" - consent
              / %x4E  ; "N" - none
              / %x55  ; "U" - updated
              / %x58  ; "X" - dynamic
Issue 137: Does hybrid tracking status need to distinguish between first party (1) and outsourcing service provider acting as a first party (s)

[PENDING REVIEW] No, in practice there may be dozens of service providers on any given request. If the designated resource is operated by a service provider acting as a first party, then the responsible first party is identified by the policy link or the owner of the origin server domain. This satisfies the use case of distinguishing between a service provider acting for some other site and the same service provider acting on one of its own sites.

5.3 Tracking Status Qualifier Values

When present, the tracking status qualifier member's value consists of a string of characters indicating what permitted uses for tracking are being used. Multiple qualifiers can be provided.

Issue 136: Resolve dependencies of the TPE on the compliance specification

The list of qualifiers is intended to match one to one to the permitted uses identified by [TRACKING-COMPLIANCE], using references to the definitions there. The list will then be updated accordingly.

qualifier meaning
a Audit: Tracking is limited to that necessary for an external audit of the service context and the data collected is minimized accordingly.
c Ad frequency capping: Tracking is limited to frequency capping and the data collected is minimized accordingly.
f Fraud prevention: Tracking is limited to that necessary for preventing or investigating fraudulent behavior and security violations; the data collected is minimized accordingly.
l Local constraints: Tracking is limited to what is required by local law, rule, or regulation and the data collected is minimized accordingly.
r Referrals: Tracking is limited to collecting referral information and the data collected is minimized accordingly.

Qualifiers that indicate limitations on tracking correspond to the specific permitted uses in [TRACKING-COMPLIANCE]. An origin server indicating one or more of those permitted uses also indicates that it conforms to the requirements associated with those permitted uses. Multiple limitation qualifiers mean that multiple permitted uses of tracking might be present and that each such use conforms to the associated requirements. All limitation qualifiers imply some form of tracking might be used and thus MUST NOT be provided with a tracking status value of N (not tracking).

Future extensions to this protocol might define additional characters as qualifiers from the ext-qualifier set (consisting of the remaining unused lowercase letters, dot, dash, and underscore). Recipients SHOULD ignore extension qualifiers that they do not understand.

The tracking qualifier value is case sensitive, as defined formally by the following ABNF.

	tracking-q    = tracking-q-v*
	tracking-q-v  = %x61   ; "a" - audit
			  / %x63  ; "c" — capping
			  / %x66  ; "f" - fraud
			  / %x6C  ; "l" - local
			  / %x72  ; "r" - referral

5.4 Tk Header Field for HTTP Responses

5.4.1 Definition

The Tk response header field is hereby defined as an OPTIONAL means for indicating the tracking status that applied to the corresponding request and as a REQUIRED means for indicating that a state-changing request has resulted in an interactive change to the tracking status.

Tk-field-name   =  "Tk"       ; case-insensitive
Tk-field-value  =  tracking-v [tracking-q] [ ";" status-id ]

The Tk field-value begins with a tracking status value (section 5.2 Tracking Status Value), optionally followed by one or more tracking qualifiers (section 5.3 Tracking Status Qualifier Values), and then optionally a semicolon and a status-id that refers to a request-specific tracking status resource (section 5.4.2 Referring to a Request-specific Tracking Status Resource).

For example, a Tk header field for a resource that claims not to be tracking would look like:

Example 2
Tk: N

whereas a Tk header field for a resource that might perform tracking (though not necessarily for every request) and conforms to the third-party requirements of [TRACKING-COMPLIANCE], while claiming the audit exception, would look like:

Example 3
Tk: 3a

5.4.2 Referring to a Request-specific Tracking Status Resource

If an origin server has multiple, request-specific tracking policies, such that the tracking status might differ depending on some aspect of the request (e.g., method, target URI, header fields, data, etc.), the origin server MAY provide an additional subtree of well-known resources corresponding to each of those distinct tracking statuses. The OPTIONAL status-id portion of the Tk field-value indicates which specific tracking status resource applies to the current request.

status-id       =  1*id-char  ; case-sensitive
id-char         =  ALPHA / DIGIT / "_" / "-" / "+" / "=" / "/"

For example, a response containing

Example 4
Tk: 1;fRx42

indicates that the target resource claims to conform to the first-party requirements of [TRACKING-COMPLIANCE] and that an applicable tracking status representation can be obtained by performing a retrieval request on


If a Tk field-value has a tracking status value of X (dynamic), then a status-id MUST be included in the field-value.

5.4.3 Indicating an Interactive Status Change

We anticipate that interactive mechanisms might be used, beyond the scope of this specification, that have the effect of asking for and obtaining prior consent for tracking, or for modifying prior indications of consent. For example, the tracking status resource's status-object defines a control member that can refer to such a mechanism. Although such out-of-band mechanisms are not defined by this specification, their presence might influence the tracking status object's response value.

When an origin server provides a mechanism via HTTP for establishing or modifying out-of-band tracking preferences, the origin server MUST indicate within the mechanism's response when a state-changing request has resulted in a change to the tracking status for that server. This indication of an interactive status change is accomplished by sending a Tk header field in the response with a tracking status value of U (updated).

Example 5
Tk: U

5.5 Tracking Status Resource

5.5.1 Site-wide Tracking Status

An origin server MUST provide a site-wide tracking status resource at the well-known identifier [RFC5785]


(relative to the URI of that origin server) for obtaining information about the potential tracking behavior of resources provided by that origin server. A tracking status resource MAY be used for verification of DNT support, as described in section 5.7 Using the Tracking Status.

A valid retrieval request (e.g., a GET in HTTP) on the well-known URI MUST result in either a successful response containing a machine-readable representation of the site-wide tracking status, as defined below, or a sequence of redirects that leads to such a representation. A user agent MAY consider failure to provide access to such a representation equivalent to the origin server not implementing this protocol. The representation MAY be cached, as described in section 5.5.5 Caching.

5.5.2 Request-specific Tracking Status

If an origin server has multiple, request-specific tracking policies, such that the tracking status might differ depending on some aspect of the request (e.g., method, target URI, header fields, data, etc.), the origin server MAY provide an additional subtree of well-known resources corresponding to each of those distinct tracking statuses. The Tk response header field (section 5.4 Tk Header Field for HTTP Responses) can include a status-id to indicate which specific tracking status resource applies to the current request.

The tracking status resource space is defined by the following URI Template [URI-TEMPLATE]:


where the value of status-id is a string of URI-safe characters provided by a Tk field-value in response to a prior request. For example, a prior response containing

Example 6
Tk: 1;ahoy

refers to the specific tracking status resource


Resources within the request-specific tracking status resource space are represented using the same format as a site-wide tracking status resource.

5.5.3 Representation

The representation of a tracking status resource shall be provided in the "application/json" format [RFC4627] and MUST conform to the ABNF for status-object (except that the members within each member-list MAY be provided in any order).

The following example tracking status representation illustrates all of the fields defined by this specification, most of which are optional.

Example 7
  "tracking": "1",
  "same-party": [
  "third-party": [
  "audit": [
  "policy": "/tracking.html",
  "control": "http://example.com/your/data"

A tracking status representation consists of a single status-object containing members that describe the tracking status applicable to the designated resource.

status-object = begin-object member-list end-object

member-list   = tracking         ns tracking-v [tracking-q]
                [ vs same-party  ns same-party-v  ]
                [ vs third-party ns third-party-v ]
                [ vs audit       ns audit-v       ]
                [ vs policy      ns policy-v      ]
                [ vs control     ns control-v     ]
                *( vs extension )

A status-object MUST have a member named tracking that contains a single character tracking status value (section 5.2 Tracking Status Value), optionally followed by one or more tracking qualifiers (section 5.3 Tracking Status Qualifier Values) .

tracking      = %x22 "tracking" %x22

For example, the following demonstrates a minimal tracking status representation that is applicable to any resource that does not perform tracking.

Example 8
{"tracking": "N"}

An OPTIONAL member named same-party MAY be provided with an array value containing a list of domain names that the origin server claims are the same party, to the extent they are referenced by the designated resource, since all data collected via those references share the same data controller.

same-party    = %x22 "same-party" %x22
same-party-v  = array-of-strings

An OPTIONAL member named third-party MAY be provided with an array value containing a list of domain names for third-party services that might be invoked while using the designated resource but do not share the same data controller as the designated resource.

third-party   = %x22 "third-party" %x22
third-party-v = array-of-strings

An OPTIONAL member named audit MAY be provided with an array value containing a list of URI references to external audits of the designated resource's tracking policy and tracking behavior in compliance with this protocol. Preferably, the audit references are to resources that describe the auditor and the results of that audit; however, if such a resource is not available, a reference to the auditor is sufficient.

audit         = %x22 "audit" %x22
audit-v       = array-of-strings

An OPTIONAL member named policy MAY be provided with a string value containing a URI-reference to a human-readable document that describes the tracking policy for the designated resource. The content of such a policy document is beyond the scope of this protocol and only supplemental to what is described by this machine-readable tracking status representation.

policy        = %x22 "policy" %x22
policy-v      = string       ; URI-reference

If the tracking status value is 1 and the designated resource is being operated by an outsourced service provider on behalf of a first party, the origin server MUST identify the responsible first party via the domain of the policy URI, if present, or by the domain owner of the origin server. If no policy URI is provided and the origin server domain is owned by the service provider, then the service provider is the first party.

An OPTIONAL member named control MAY be provided with a string value containing a URI-reference to a resource for giving the user control over personal data collected by the designated resource (and possibly other resources); a control member SHOULD be provided if the tracking status value indicates prior consent (C). Such a control resource might include the ability to review past data collected, delete some or all of the data, provide additional data (if desired), or opt-in, opt-out, or otherwise modify an out-of-band consent status regarding data collection. The design of such a resource, the extent to which it can provide access to that data, and how one might implement an out-of-band consent mechanism is beyond the scope of this protocol.

control       = %x22 "control" %x22
control-v     = string       ; URI-reference

Additional extension members MAY be provided in the status-object to support future enhancements to this protocol. A user agent SHOULD ignore extension members that it does not recognize.

extension     = object

array-of-strings = begin-array
                   [ string *( vs string ) ]

ns            = <name-separator  (:), as defined in [[!RFC4627]]>
vs            = <value-separator (,), as defined in [[!RFC4627]]>

begin-array   = <begin-array     ([), as defined in [[!RFC4627]]>
end-array     = <end-array       (]), as defined in [[!RFC4627]]>
begin-object  = <begin-object    ({), as defined in [[!RFC4627]]>
end-object    = <end-object      (}), as defined in [[!RFC4627]]>
object        = <object, as defined in [[!RFC4627]]>
string        = <string, as defined in [[!RFC4627]]>
true          = <true,   as defined in [[!RFC4627]]>
false         = <false,  as defined in [[!RFC4627]]>
null          = <null,   as defined in [[!RFC4627]]>

Note that the tracking status resource space applies equally to both first-party and third-party services. An example of a third-party tracking status is

Example 9
  "tracking": "3",
  "policy": "/privacy.html",
  "control": "/your/data",

5.5.4 Status Checks are Not Tracked

When sending a request for the tracking status, a user agent SHOULD include any cookie data [COOKIES] (set prior to the request) that would be sent in a normal request to that origin server, since that data might be needed by the server to determine the current tracking status. For example, the cookie data might indicate a prior out-of-band decision by the user to opt-out or consent to tracking by that origin server.

All requests on the tracking status resource space, including the site-wide tracking status resource, MUST NOT be tracked, irrespective of the presence, value, or absence of a DNT header field, cookies, or any other information in the request. In addition, all responses to those requests, including the responses to redirected tracking status requests, MUST NOT have Set-Cookie or Set-Cookie2 header fields and MUST NOT have content that initiates tracking beyond what was already present in the request. A user agent SHOULD ignore, or treat as an error, any Set-Cookie or Set-Cookie2 header field received in such a response.

5.5.5 Caching

If the tracking status is applicable to all users, regardless of the received DNT-field-value or other data received via the request, then the response SHOULD be marked as cacheable and assigned a time-to-live (expiration or max-use) that is sufficient to enable shared caching but not greater than the earliest point at which the service's tracking behavior might increase. For example, if the tracking status response is set to expire in seven days, then the earliest point in time that the service's tracking behavior can be increased is seven days after the policy has been updated to reflect the new behavior, since old copies might persist in caches until the expiration is triggered. A service's tracking behavior can be reduced at any time, with or without a corresponding change to the tracking status resource.

If the tracking status is only applicable to all users that have the same DNT-field-value, then the response MUST either be marked with a Vary header field that includes "DNT" in its field-value or marked as not reusable by a shared cache without revalidation with a Cache-Control header field containing one of the following directives: "private", "no-cache", "no-store", or "max-age=0".

If the tracking status is only applicable to the specific user that requested it, then the response MUST include a Cache-Control header field containing one of the following directives: "private", "no-cache", or "no-store".

Regardless of the cache-control settings, it is expected that user agents will check the tracking status of a service only once per session (at most). A public Internet site that intends to change its tracking status to increase tracking behavior MUST update the tracking status resource in accordance with that planned behavior at least twenty-four hours prior to activating that new behavior on the service.

A user agent that adjusts behavior based on active verification of tracking status, relying on cached tracking status responses to do so, SHOULD check responses to its state-changing requests (e.g., POST, PUT, DELETE, etc.) for a Tk header field with the U tracking status value, as described in section 5.4.3 Indicating an Interactive Status Change.

5.6 Status Code for Tracking Required

If an origin server receives a request with DNT:1, does not have out-of-band consent for tracking this user, and wishes to deny access to the requested resource until the user provides some form of user-granted exception or consent for tracking, then the origin server SHOULD send an HTTP error response with a status code of 409 (Conflict) and a message body that describes why the request has been refused and how one might supply the required consent or exception to avoid this conflict [HTTP11].

The 409 response SHOULD include a user authentication mechanism in the header fields and/or message body if user login is one of the ways through which access is granted.

5.7 Using the Tracking Status


This section is for collecting use cases that describe questions a user agent might have about tracking status and how the protocol can be used to answer such questions. More cases are needed.

5.7.1 Discovering Deployment

The presence of a site-wide tracking status representation is a claim that the service conforms to this protocol for a given user agent. Hence, deployment of this protocol for a given service can be discovered by making a retrieval request on the site-wide tracking resource /.well-known/dnt relative to the service URI.

If the response is an error, then the service does not implement this standard. If the response is a redirect, then follow the redirect to obtain the tracking status (up to some reasonable maximum of redirects to avoid misconfigured infinite request loops). If the response is successful, obtain the tracking status representation from the message payload, if possible, or consider it an error.

5.7.2 Preflight Checks

A key advantage of providing the tracking status at a resource separate from the site's normal services is that the status can be accessed and reviewed prior to making use of those services and prior to making requests on third-party resources referenced by those services.

A user agent MAY check the tracking status for a designated resource by first making a retrieval request for the site-wide tracking status representation, as described above, and then parsing the representation as JSON to extract the Javascript status-object. If retrieval is unsuccessful or parsing results in a syntax error, the user agent SHOULD consider the site to be non-conformant with this protocol.

The status-object is supposed to have a member named tracking containing the tracking status value. The meaning of each tracking status value is defined in section 5.2 Tracking Status Value.

If the tracking status value is N, then the origin server claims that no tracking is performed for the designated resource for at least the next 24 hours or until the Cache-Control information indicates that this response expires.

If the tracking status value is not N, then the origin server claims that it might track the user agent for requests on the URI being checked for at least the next 24 hours or until the Cache-Control information indicates that this response expires.

6. User-Granted Exceptions

6.1 Overview

This section is non-normative.

User-granted exceptions to Do Not Track, including site-specific exceptions, are managed by the user agent. A resource should rely on the DNT header it receives to determine the user's preference for tracking with respect to that particular request. An API is provided so that sites may request and check the status of exceptions for tracking.

We anticipate that many user-agents might provide a prompt to users when this API is used, or to store exceptions. Questions of user interface specifics — for granting, configuring, storing, syncing and revoking exceptions — are explicitly left open to implementers.

Issue 144: What constraints on user agents should be imposed for user/granted exceptions

[OPEN] but mostly addressed in the proposal here.

6.2 Motivating Principles and Use Cases

This section is non-normative.

The following principles guide the design of user-agent-managed exceptions.

When asking for a site-specific exception, the top-level domain making the request may be making some implicit or explicit claims as to the actions and behavior of its third parties; for this reason, it might want to establish exceptions for only those for which it is sure that those claims are true. (Consider a site that has some trusted advertisers and analytics providers, and some mashed-up content from less-trusted sites). For this reason, there is support both for explicitly named sites, as well as support for granting an exception to all third-parties on a given site (site-wide exception, using the conceptual wild-card "*").

There are some cases in which a user may desire a site to be allowed to track them on any top-level domain. An API is provided so that the site and the user may establish such a web-wide exception.

6.3 Exception model

6.3.1 Introduction

This section describes the effect of the APIs in terms of a logical processing model; this model describes the behavior, but should not be read as mandating any specific implementation.

This API considers exceptions which are double-keyed to two domains: the site, and the target. A user might — for instance — want AnalytiCo to be allowed to track them on Example News, but not on Example Medical. To simplify language used in this API specification, we define three terms:

  • Top-Level Domain (TLD) is the domain name of the top-level document origin of this DOM: essentially the fully qualified domain name in the address bar.
  • A target site is a domain name which is the target of an HTTP request, and which may be an origin for embedded resources on the indicated top-level domain.
  • The document origin of a script is the domain of origin of the document that caused that script to be loaded (not necessarily the same as the origin of the script itself).

For instance, if the document at http://web.exnews.com/news/story/2098373.html references the resources http://exnews.analytico.net/1x1.gif and http://widgets.exsocial.org/good-job-button.js, the top-level domain is web.exnews.com; exnews.analytico.net and widgets.exsocial.org are both targets.

Issue 112: How are sub-domains handled for site-specific exceptions?

[PENDING REVIEW] Should a request for a tracking exception apply to all subdomains of the first party making the request? Or should a first party explicitly list the subdomains that it's asking for? Similarly, should third-party subdomains be allowed (e.g. *.tracker.com)?
Proposal: Exceptions are requested for fully-qualified domain names.

The domains that enter into the behavior of the APIs include:

  • As described above, the document origin active at the time of the call, and;
  • Domain names passed to the API.

Domains that enter into the decision over what DNT header to be sent in a given HTTP request include:

  • The top-level domain of the current context;
  • The target of the HTTP request.

Note that these strict, machine-discoverable, concepts may not match the definitions of first and third party; in particular, sites themselves need to determine (and signal) when they get 'promoted' to first party by virtue of user interaction; the UA will not change the DNT header it sends them.

The calls cause the following steps to occur:

  • First, the UA somehow confirms with the user that they agree to the grant of exception, if not already granted;
  • If they agree, then the UA adds to its local database one or more site-pair duplets [document-origin, target]; one or other of these may be a wild-card ("*");
  • While the user is browsing a given site (top-level domain), and a DNT header is to be sent to a target domain, if the duplet [top-level domain, target domain] matches any duplet in the database, then a DNT:0 header is sent, otherwise DNT:1 is sent.

Note that a site may record no that it has previously asked for, and been denied, an exception, if it wishes to avoid repeatedly asking the user for an exception.

6.3.2 Exception use by browsers

If a user agrees to allow tracking by a target on the top-level domain, this should result in two user-agent behaviors:

  1. If requests to the target for resources that are part of the DOM for pages on top-level domain include a DNT header, that header MUST be DNT:0.
  2. Responses to the JavaScript API indicated should be consistent with this user preference (see below).
Issue 159: How do we allow sites that mash-in ad-supported content to maintain their own trusted third parties?

This model does not support mashed-up content which is in turn supported by ads; it's not clear how to distinguish between embedded content which is embedding ads (and hence the top-level domain stays the same) and embedded content that should start a new context.
Proposal: For this version of the specification, we don't address this corner case.

User-agents MUST handle each API request as a 'unit', granting and maintaining it in its entirety, or not at all. That means that a user-agent MUST NOT indicate to a site that a request for targets {a, b, c} has been granted, and later remove only one or two of {a, b, c} from its logical database of remembered grants. This assures sites that the set of sites they need for operational integrity is treated as a unit. Each separate call to an API is a separate unit.

When a user-agent receives an API request for an exception that already exists (i.e. the grant is recorded in its database), it SHOULD bypass asking the user to confirm, and simply re-confirm the grant to the caller.


It is left up to individual user-agent implementations how to determine and how and whether to store users' tracking preferences.

When an explicit list of domains is provided through the API, their names might mean little to the user. The user might, for example, be told that such-and-such top-level domain is asking for an exception for a specific set of sites, rather than listing them by name; or the user-agent may decide to ask the user for a site-wide exception, effectively ignoring the list of domain names, if supplied.

Conversely, if a wild-card is used, the user may be told that the top-level domain is asking for an exception for all third-parties that are, or will be, embedded in it.

Issue 111: Different DNT values to signify existence of user-granted exception

[POSTPONED] Should the user agent send a different DNT value to a first party site if there exist user-granted exceptions for that first party? (e.g. DNT:2 implies "I have Do Not Track enabled but grant permissions to some third parties while browsing this domain")
Proposal: A previous proposal was that it can add itself to the list (i.e. an exception for [site, site]) and then it will get DNT:0, but DNT:0 to a first party means something different (that it can pass data to third parties, and tracking is permitted). It would be better to have an indication in the DNT header that one or more site-specific exceptions exist for the given target (i.e. that there is at least one duplet in the database with target as its first host name), for example "DNT:1E" where E means you are a first party with one or more active exceptions.

6.4 JavaScript API for Site-specific Exceptions

6.4.1 API to request site-specific exceptions

interface NavigatorDoNotTrack {
    void requestSiteSpecificTrackingException (
           TrackingResponseCallback callback,
           optional sequence<DOMString> arrayOfDomainStrings,
           optional optional siteName,
           optional optional explanationString,
           optional optional detailURI
Called by a page to request or confirm a user-granted tracking exception.
Return type: void
[Callback, NoInterfaceObject]
interface TrackingResponseCallback {
    void handleEvent (integer granted);
The callback is called by the user agent to indicate the user's response.
Return type: void

The requestSiteSpecificTrackingException method takes one mandatory argument:

  • callback, a method that will be called when the request is complete.

It also takes four optional arguments:

  • arrayOfDomainStrings, a JavaScript array of strings,
  • siteName, a user-readable string for the name of the top-level domain,
  • explanationString, a short explanation of the request, and
  • detailURI, a location at which further information about this request can be found.

If the request does not include the arrayOfDomainStrings, then this request is for a site-wide exception. Otherwise each string in arrayOfDomainStrings specifies a target. When called, requestSiteSpecificTrackingException MUST return immediately, then asynchronously determine whether the user grants the requested exception(s).

If the list arrayOfDomainStrings is supplied, the user-agent MAY choose to ask the user to grant a site-wide exception. If it does so, and the user agrees, it MUST indicate this in the response callback.

The execution of this API and the use of the resulting permission (if granted) use the 'implicit' parameter, when the API is called, the document origin. This forms the first part of the duplet in the logical model, and hence in operation will be compared with the top-level domain.

The granted parameter passed to the callback is the user's response; The response

  • 0 indicates that user does not grant the exception on top-level domain for the indicated targets.
  • 1 indicates that the request was for specific targets and the the user grants an exception on top-level domain for those specific targets.
  • 2 indicates the user grants a site-wide exception on top-level domain for all targets; the request may have been for specific targets or for a site-wide exception.

If permission is granted for an explicit list, then the set of duplets (one per target):

[document-origin, target]

is added to the database of remembered grants.

If permission is granted for a site-wide exception, then the duplets:

[document-origin, * ]

is added to the database of remembered grants.

A particular response to the API — like a DNT response header — is only valid immediately, and users' preferences may change.

A user agent MAY use an interactive method to ask the user about their preferences, so sites SHOULD NOT assume that the callback function will be called immediately.

6.4.2 API to Cancel a Site-specific Exception

interface NavigatorDoNotTrack {
    boolean removeSiteSpecificTrackingException ();
Ensures that the database of remembered grants no longer contains any duplets for which the first part is the current document origin; i.e., no duplets [document-origin, target] for any target. There is no callback. After the call has been made, it is assured that there are no site-specific or site-wide exceptions for the given top-level-domain.
No parameters.
Return type: boolean

This returns a boolean indicating, when true, that the call has succeeded, and that the database of grants no longer contains, or very soon will no longer contain, the indicated grant(s); when false, some kind of processing error occurred.

6.5 JavaScript API for Web-wide Exceptions

6.5.1 API to Request a Web-wide Exception

interface NavigatorDoNotTrack {
    void requestWebWideTrackingException (
           TrackingResponseCallback callback,
           optional  siteName,
           optional optional explanationString,
           optional optional detailURI
If permission is granted, then the single duplet [ * , document-origin] is added to the database of remembered grants. The parameters are as described above in the request for site-specific exceptions.
Return type: void

Users may wish to configure exceptions for a certain trusted tracker across all sites. This API requests the addition of a web-wide grant for a specific site, to the database.

6.5.2 API to cancel a web-wide exception

interface NavigatorDoNotTrack {
    boolean removeWebWideTrackingException ();
Ensures that the database of remembered grants no longer contains the duplet [ * , document-origin]. There is no callback. After the call has been made, the indicated pair is assured not to be in the database. The same matching as is used for determining which header to send is used to detect which entry (if any) to remove from the database.
No parameters.
Return type: boolean

This returns a boolean indicating, when true, that the call has succeeded, and that the database of grants no longer contains, or very soon will no longer contain, the indicated grant; when false, some kind of processing error occurred.

6.6 Querying a host's exception status

Issue 160: Do we need an exception-query API?

[PENDING REVIEW] It might be useful, and 'complete the model', if we had a JS API that told a host what its current exception status is in a given context. See proposal here.
Proposal: Specifically, an API QueryExceptionStatus() which examines the document origin of the script, the current top-level domain and returns an empty string if no DNT header would be sent to that document origin, or the exact DNT header (DNT:1 or DNT:0) that would be sent otherwise.

interface NavigatorDoNotTrack {
    DOMString requestDNTStatus ();
Returns the same string value that would be sent in a DNT-field-value (section 4.2 DNT Header Field for HTTP Requests) to a target that is the document-origin of the request, in the context of the current top-level domain. If no DNT header would be sent (e.g. because a tracking preference is not enabled) the return value is null.
No parameters.
Return type: DOMString

6.7 Transfer of an exception to another third party

A site may request an exception for one or more third party services used in conjunction with its own offer. Those third party services may wish to use other third parties to complete the request in a chain of interactions. The first party will not necessarily know in advance whether a known third party will use some other third parties.

If a user-agent sends a tracking exception to a given combination of origin server and a named third party, the user agent will send DNT:0 to that named third party. By receiving the DNT:0 header, the named third party acquires the permission to track the user agent and collect the data and process it in any way allowed by the legal system it is operating in.

Furthermore, the named third party receiving the DNT:0 header acquires at least the right to collect data and process it for the given interaction and any secondary use unless it receives a DNT:1 header from that particular identified user agent.

The named third party is also allowed to transmit the collected data for uses related to this interaction to its own sub-services and sub-sub-services (transitive permission). The tracking permission request triggered by the origin server is thus granted to the named third party and its sub-services. This is even true for sub-services that would normally receive a DNT:1 web-wide preference from the user-agent if the user agent interacted with this service directly.

For advertisement networks this typically would mean that the collection and auction system chain can use the data for that interaction and combine it with existing profiles and data. The sub-services to the named third party do not acquire an independent right to process the data for independent secondary uses unless they, themselves, receive a DNT:0 header from the user agent (as a result of their own request or the request of a first-party). In our example of advertisement networks that means the sub-services can use existing profiles in combination with the data received, but they can not store the received information into a profile until they have received a DNT:0 of their own.

A named third party acquiring an exception with this mechanism MUST make sure that sub-services it uses acknowledge this constraint by requiring the use of the appropriate tracking status value and qualifier, which is "XX" (such as "tl"), from its sub-sub-services.

The permission acquired by the DNT mechanism does not override retention limitations found in the legal system the content provider or the named third party are operating in.

Issue 168: What is the correct way for sub-services to signal that they are taking advantage of a transferred exception?

When the status values and qualifiers are fixed, the penultimate paragraph will probably need adjusting to match. The use of "tl" (which meant "tracking but only in accordance with local laws" when this text was written) doesn't seem right, as the text talks, essentially, of the sub-sub-service acting on behalf of the site that received the DNT:0 header, which might suggest something more like "CS" (service provision to a third-party that received consent).

6.8 User interface guidelines

This section is non-normative.

User agents are free to implement exception management user interfaces as they see fit. Some agents might provide a prompt to the user at the time of the request. Some agents might allow users to configure this preference in advance. In either case, the user agent responds with the user's preference.

In general, it is expected that the site will explain, in its online content, the need for an exception, and the consequences of granting or denying an exception, to the user, and guide. The call to the API and the resulting request for user confirmation should not be a 'surprise' to the user, or require much explanation on the part of the user-agent.

A user agent that chooses to implement a prompt to present tracking exception requests to the user might provide an interface like the following:

Example 10
Example News (web.exnews.com) would like to confirm
that you permit tracking by a specific set of sites (click
here for their names).

Example News says:
  These sites allow Example News to see how we're
  doing, and provide useful features of the Example News
  experience.     [More info]

[Allow Tracking]  [Deny Tracking Request]

In this example, the domains listed are those specified in arrayOfDomainStrings, the phrase Example News is from siteName, and the explanationString is displayed for the user with a More info link pointing to detailURI.

The user agent might then store that decision, and answer future requests based on this stored preference. A user agent might provide the user with an interface to explicitly remove (or add) user-granted exceptions.

Users might not configure their agents to have simple values for DNT, but use different browsing modes or other contextual information to decide on a DNT value. What algorithm a user agent employs to determine DNT values (or the lack thereof) is out of the scope of this specification.

In some user-agent implementations, decisions to grant exceptions may have been made in the past (and since forgotten) or may have been made by other users of the device. Thus, exceptions may not always represent the current preferences of the user. Some user agents might choose to provide ambient notice that user-opted tracking is ongoing, or easy access to view and control these preferences. Users may desire options to edit exceptions either at the time of tracking or in a separate user interface. This might allow the user to edit their preferences for a site they do not trust without visiting that site.

Issue 140: Do we need site-specific exceptions, i.e., concrete list of permitted third parties for a site?

[PENDING REVIEW] In this section; yes, as some sites may have a mix of trusted/needed third parties, and others that either don't need to track, or aren't as trusted, or both. But all sites are (a) told what they got granted (list, or *) and (b) are assured that requests will be treated 'atomically'.

6.9 Exceptions without a DNT header

Sites might wish to request exceptions even when a user arrives without a DNT header. Users might wish to grant affirmative permission to tracking on or by certain sites even without expressing general tracking preferences.

User agents MAY instantiate NavigatorDoNotTrack.requestSiteSpecificTrackingException even when navigator.doNotTrack is null. Sites SHOULD test for the existence of requestSiteSpecificTrackingException before calling the method. If an exception is granted in this context and the user-agent stores that preference, a user agent may send a DNT:0 header even if a tracking preference isn't expressed for other requests. Persisted preferences MAY also affect which header is transmitted if a user later chooses to express a tracking preference.


Users might not configure their agents to have simple values for DNT, but use different browsing modes or other contextual information to decide on a DNT value. What algorithm a user agent employs to determine DNT values (or the lack thereof) is out of the scope of this specification.

6.10 Fingerprinting

By storing a client-side configurable state and providing functionality to learn about it later, this API might facilitate user fingerprinting and tracking. User agent developers ought to consider the possibility of fingerprinting during implementation and might consider rate-limiting requests or using other heuristics to mitigate fingerprinting risk. User agents SHOULD clear stored user-granted exceptions when the user chooses to clear cookies or other client-side state.

A. Acknowledgements

This specification consists of input from many discussions within and around the W3C Tracking Protection Working Group, along with written contributions from Nick Doty (W3C/MIT), Rob van Eijk (Invited Expert), Roy T. Fielding (Adobe), Tom Lowenthal (Mozilla), Jonathan Mayer (Stanford), Aleecia M. McDonald (Mozilla), Matthias Schunter (IBM), John Simpson (Consumer Watchdog), David Singer (Apple), David Wainberg (Network Advertising Initiative), Rigo Wenning (W3C/ERCIM), Shane Wiley (Yahoo!), and Andy Zeigler (Microsoft).

The DNT header field is based on the original Do Not Track submission by Jonathan Mayer (Stanford), Arvind Narayanan (Stanford), and Sid Stamm (Mozilla). The DOM API for NavigatorDoNotTrack is based on the Web Tracking Protection submission by Andy Zeigler, Adrian Bateman, and Eliot Graff (Microsoft). Many thanks to Robin Berjon for ReSpec.js.

B. References

B.1 Normative references

D. Crocker and P. Overell. Augmented BNF for Syntax Specifications: ABNF. January 2008. Internet RFC 5234. URL: http://www.ietf.org/rfc/rfc5234.txt
R. Fielding; et al. Hypertext Transfer Protocol - HTTP/1.1. June 1999. Internet RFC 2616. URL: http://www.ietf.org/rfc/rfc2616.txt
Robin Berjon; Travis Leithead; Silvia Pfeiffer; Erika Doyle Navara; Edward O'Connor; Ian Hickson. The Navigator object - System state and capabilities - HTML5. 28 September 2012. Editors' draft. (Work in progress.) URL: http://dev.w3.org/html5/spec/system-state-and-capabilities.html#the-navigator-object
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Internet RFC 2119. URL: http://www.ietf.org/rfc/rfc2119.txt
D. Crockford. The application/json Media Type for JavaScript Object Notation (JSON) July 2006. Internet RFC 4627. URL: http://www.ietf.org/rfc/rfc4627.txt
Justin Brookman; Sean Harvey; Erica Newland; Heather West. Tracking Compliance and Scope. 2 October 2012. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2012/WD-tracking-compliance-20121002/
Cameron McCormack. Web IDL. 27 September 2011. W3C Working Draft. (Work in progress.) URL: http://www.w3.org/TR/2011/WD-WebIDL-20110927/

B.2 Informative references

Adam Barth. HTTP State Management Mechanism. April 2011. Internet Proposed Standard RFC 6265. URL: http://www.rfc-editor.org/rfc/rfc6265.txt
Joshua Gomez; Travis Pinnick; Ashkan Soltani. KnowPrivacy. 1 June 2009. URL: http://www.knowprivacy.org/report/KnowPrivacy_Final_Report.pdf
Mark Nottingham; Eran Hammer-Lahav. Defining Well-Known Uniform Resource Identifiers (URIs). April 2010. Internet Proposed Standard RFC 5785. URL: http://www.rfc-editor.org/rfc/rfc5785.txt
Joe Gregorio; Roy T. Fielding; Marc Hadley; Mark Nottingham; David Orchard. URI Template. March 2012. Internet RFC 6570. URL: http://www.rfc-editor.org/rfc/rfc6570.txt