This specification defines the DNT request header field as an
HTTP mechanism for expressing a user's preference regarding tracking,
an HTML DOM property to make that expression readable by scripts, and
APIs that allow scripts to register exceptions granted by
the user. It also defines mechanisms for sites to communicate whether
and how they honor a received preference, including
well-known resources for retrieving preflight tracking status,
a media type for representing tracking status information, and the
Tk
response header field for confirming tracking status.
This document is an editors' straw man reflecting a snapshot of live discussions within the Tracking Protection Working Group. It does not necessarily constitute working group consensus. This draft has been prepared using the DNT github repository and its associated issues list. However, see the previous issue tracking system for working group decisions prior to 2017.
The World Wide Web consists of billions of resources interconnected through the use of hypertext. Hypertext provides a simple, page-oriented view of the information provided by those resources, which can be traversed by selecting links, manipulating controls, and supplying data via forms and search dialogs.
A Web page is often composed of many 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. The user's experience is seamless, even if the page has been composed from the results of many network interactions with multiple servers. From the user's perspective, they are simply visiting and interacting with a single Web site: all of the technical details and protocol mechanisms used to compose a page to represent that site are hidden behind the scenes.
Web site owners often collect data regarding usage of their sites, for a variety of purposes, including what led a user to visit the site (referrals), how effective the user experience is within the site (web analytics), and the nature of who is using the site (audience segmentation). In some cases, the data collected is used to dynamically adapt content (personalization) or advertising presented to the user (targeted advertising). Data collection often occurs through insertion of embedded elements on each page, resulting in a stream of data that connects a user's activity across multiple pages. A survey of these techniques and their privacy implications can be found in [[KnowPrivacy]].
Users need a mechanism to express their own preferences regarding tracking that is both simple to configure and efficient when implemented. However, merely expressing a preference does not imply that all recipients will comply. In some cases, a server might be dependent on some forms of tracking and unwilling or unable to turn that off. In other cases, a server might perform only limited forms of tracking that would be acceptable to most users. Therefore, servers need mechanisms for communicating their own tracking behavior, requesting consent, and storing a user-granted exception once the user has made an informed choice.
This specification extends Hypertext Transfer Protocol (HTTP) semantics [[!RFC7231]] to communicate a user's tracking preference, if any, and an origin server's tracking behavior. The DNT request header field is defined for communicating the user's tracking preference for the target resource. A well-known URI for a tracking status resource and the Tk response header field are defined for communicating the server's tracking behavior. In addition, JavaScript APIs are defined for enabling scripts to determine DNT status and register a user-granted exception.
This specification does not define requirements on what a recipient needs to do to comply with a user's expressed tracking preference, except for the means by which such compliance is communicated. Instead, the tracking status provides the ability to identify a set of compliance regimes to which the server claims to comply, with the assumption being that each regime defines its own requirements on compliant behavior. For example, [[TCS]] is a work-in-progress that intends to define such a compliance regime.
The following terms are used as defined by HTTP/1.1 syntax [[!RFC7230]] and semantics [[!RFC7231]]: client, server, origin server, user agent, sender, recipient, request, response, message, intermediary, proxy, cache, uri-host, authority, header field, target resource, resource, and representation.
The following terms are used as defined by HTML [[!HTML5]]: active document, document.domain, effective script origin, responsible document, browsing context, nested browsing context, and top-level browsing context.
Tracking is the collection of data regarding a particular user's activity across multiple distinct contexts and the retention, use, or sharing of data derived from that activity outside the context in which it occurred. A context is a set of resources that are controlled by the same party or jointly controlled by a set of parties.
A network interaction is a single HTTP request and its corresponding response(s): zero or more interim (1xx) responses and a single final (2xx-5xx) response.
A user action is a deliberate action by the user, via configuration, invocation, or selection, to initiate a network interaction. Selection of a link, submission of a form, and reloading a page are examples of user actions. User activity is any set of such user actions.
A user is a natural person who is making, or has made, use of the Web.
A party is a natural person, a legal entity, or a set of legal entities that share common owner(s), common controller(s), and a group identity that is easily discoverable by a user. Common branding or providing a list of affiliates that is available via a link from a resource where a party describes DNT practices are examples of ways to provide this discoverability.
With respect to a given user action, a first party is a party with which the user intends to interact, via one or more network interactions, as a result of making that action. Merely hovering over, muting, pausing, or closing a given piece of content does not constitute a user's intent to interact with another party.
In some cases, a resource on the Web will be jointly controlled by two or more distinct parties. Each of those parties is considered a first party if a user would reasonably expect to communicate with all of them when accessing that resource. For example, prominent co-branding on the resource might lead a user to expect that multiple parties are responsible for the content or functionality.
For any data collected as a result of one or more network interactions resulting from a user's action, a third party is any party other than that user, a first party for that user action, or a service provider acting on behalf of either that user or that first party.
Access to Web resources often involves multiple parties that might process the data received in a network interaction. For example, domain name services, network access points, content distribution networks, load balancing services, security filters, cloud platforms, and software-as-a-service providers might be a party to a given network interaction because they are contracted by either the user or the resource owner to provide the mechanisms for communication. Likewise, additional parties might be engaged after a network interaction, such as when services or contractors are used to perform specialized data analysis or records retention.
For the data received in a given network interaction, a service provider is considered to be the same party as its contractee if the service provider:
A party collects data received in a network interaction if that data remains within the party’s control after the network interaction is complete.
A party uses data if the party processes the data for any purpose other than storage or merely forwarding it to another party.
A party shares data if it transfers or provides a copy of that data to any other party.
Data is permanently de-identified when there exists a high level of confidence that no human subject of the data can be identified, directly or indirectly (e.g., via association with an identifier, user agent, or device), by that data alone or in combination with other retained or available information.
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]].
This specification uses the Augmented Backus-Naur Form (ABNF) notation of [[!RFC5234]] to define network protocol syntax and WebIDL [[!WEBIDL]] to define scripting APIs. Conformance criteria and considerations regarding error handling are defined in Section 2.5 of [RFC7230].
How to throw a DOMexception and the exceptions named "InvalidStateError", "SecurityError", and "SyntaxError" are defined in [[!WEBIDL]].
Promise objects are defined in [[ECMASCRIPT]]; the phrases promise-call, resolve promise, reject promise, upon fulfillment, and upon rejection are used in accordance with [[PromiseGuide]].
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 recipients of that preference to adjust tracking behavior accordingly or to reach a separate agreement with the user that satisfies all parties.
Key to that notion of expression is that the signal sent MUST reflect the user's preference, not the choice of some vendor, institution, site, or network-imposed mechanism outside the user's control; this applies equally to both the general preference and exceptions. 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 (see ).
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 user's 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
.
Implementations of HTTP that are not under control of the user MUST NOT add, delete, or modify a tracking preference. 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. However, 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).
An HTTP intermediary MUST NOT add, delete, or modify a tracking preference expression in a request forwarded through that intermediary unless the intermediary has been specifically installed or configured to do so by the user making the request. For example, an Internet Service Provider MUST NOT inject DNT:1 on behalf of all users who have not expressed a preference.
User agents often include user-installable extensions, also known as add-ons or plug-ins, that are capable of modifying configurations and making network requests. From the user's perspective, these extensions are considered part of the user agent and ought to respect the user's configuration of a tracking preference. The user agent as a whole is responsible for ensuring conformance with this protocol, to the extent possible, which means the user agent core and each extension are jointly responsible for conformance. However, there is no single standard for extension interfaces. A user agent that permits such extensions SHOULD provide an appropriate mechanism for extensions to determine the user's tracking preference.
A user agent extension MUST NOT alter the tracking preference expression or its associated configuration unless the act of installing and enabling that extension is an explicit choice by the user for that tracking preference, or the extension itself complies with all of the requirements this protocol places on a user agent.
Likewise, software outside of the user agent might filter network traffic or cause a user agent's configuration to be changed. Software that alters a user agent configuration MUST adhere to the above requirements on a user agent extension. Software that filters network traffic MUST adhere to the above requirements on an HTTP intermediary.
Aside from the above requirements, we do not specify how the 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 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
).
A 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.
When a user has enabled a tracking preference, that preference needs to be expressed to all mechanisms that might perform or initiate tracking.
When enabled, a tracking preference is expressed as either:
| DNT | meaning |
|---|---|
| 1 | This user prefers not to be tracked on this request. |
| 0 | This user prefers to allow tracking on this request. |
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.
The DNT header field is a mechanism for expressing the
user's tracking preference in an HTTP request ([[!RFC7230]]).
At most one DNT header field can be present in a valid request.
DNT-field-name = "DNT" DNT-field-value = ( "0" / "1" ) *DNT-extension
A user agent MUST NOT generate a DNT header field if the
user's tracking preference is not enabled.
A user agent MUST generate a DNT header field with a
field-value that begins with the numeric character "1" if the user's
tracking preference is enabled, their preference is for
DNT:1, and no exception has been granted for the
target resource (see ).
A user agent MUST generate a DNT header field with a
field-value that begins with the numeric character "0" if the user's
tracking preference is enabled and their preference is for
DNT:0, or if an exception has been granted for
the target resource.
A proxy MUST NOT generate a DNT header field unless it has
been specifically installed or configured to do so by the user
making the request and adheres to the above requirements as if it
were a user agent.
GET /something/here HTTP/1.1 Host: example.com DNT: 1
The remainder of the DNT field-value, after the initial character, is reserved for future extensions. 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 ().
DNT-extension = %x21 / %x23-2B / %x2D-5B / %x5D-7E
; excludes CTL, SP, DQUOTE, comma, backslash
For example, additional characters might indicate modifiers to the
main preference expressed by the first digit, such that the main
preference will be understood if the recipient does not understand
the extension. Hence, a 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.
User agents that do not implement DNT extensions MUST NOT send DNT-extension characters in the DNT field-value. Servers that do not implement DNT extensions SHOULD ignore anything beyond the first character.
This DNT-extension feature is speculative because no known extensions have been defined; implementers that do not read this specification are likely to assume that DNT only has the fixed values of "0" or "1". Furthermore, the potential benefits of this mechanism are unclear given that extension information could be supplied using separate request header fields. Inappropriate extensions to the "1" value might cause the user's requests to be more easily fingerprinted.
The Navigator.doNotTrack property enables
a client-side script with read access to the
Navigator object
[[!HTML5]] to determine what DNT header field value would be
sent to the effective script origin, taking into account the
user's general preference (if any) and user-granted exceptions
applicable to the target domain when referenced by the
active document's top-level browsing context.
partial interface Navigator {
readonly attribute DOMString? doNotTrack;
};
The value is null if no DNT header field would be
sent (e.g., because a tracking preference is not enabled
and no user-granted exception is applicable);
otherwise, the value is a string beginning with "0" or "1",
possibly followed by DNT-extension characters.
Specifically, the value of Navigator.doNotTrack for a given
script is either null or the string value that would be
sent in a DNT field-value
()
in a request to a target resource at the
effective script origin (the current document.domain of
the script's responsible document) when that request is due to
an embedded reference from this site (the document.domain of
the top-level browsing context's active document).
Ideally, the value of Navigator.doNotTrack ought to reflect the current set of user-granted exceptions in effect when the attribute is read. In practice, however, the value might only reflect the value that was in effect when the script was initiated.
A user's tracking preference is intended to apply in general, regardless of the protocols being used for Internet communication. However, it is beyond the scope of this specification to define how a user's tracking preference might be communicated via protocols other than HTTP.
Content providers might wish to prompt visitors to opt in
to
tracking for behavioral advertising or similar purposes when they
arrive with the Do Not Track setting enabled. However, granting an
exception in one context (e.g., while browsing a news site) does not
imply that exception is applicable to other contexts (e.g., browsing
an unrelated medical site). Furthermore, users might wish to view or
edit all the exceptions they've granted in a single, consistent user
interface, rather than managing preferences in a different way on
every content provider or tracker's privacy page.
A user-granted exception is the record of a decision by the user to grant consent for tracking (DNT:0) on future requests from a given site to a set of target domains. Both site and target are scoped by domain, similar to the existing domain scope of cookies (Section 5.3.1 of [[!HTML5]]), to avoid prompting the user for every subdomain of a site and every target resource that might be referenced.
A client-side database can be used for persistent storage of user-granted exceptions, such that permission to send DNT:0 is obtained by a site and stored via a JavaScript API. However, we only define the API (below); the choice of storage mechanism is left to each implementation. In comparison to the use of cookies to manage consent, an exception database and APIs provide more transparency and better user control, while also providing better persistence of those exceptions for sites.
There are two primary domain concepts involved in the processing of user-granted exceptions:
A user-granted exception is site-specific if the exception is limited to requests embedded in, or referred by, a given site domain; otherwise, the exception is web-wide because it applies to the target domain regardless of the referring site. For example, a user might wish to grant a certain target domain a web-wide exception for the purpose of audience measurement across multiple sites, perhaps in exchange for some incentive.
When asking for consent to record a site-specific exception, a site might make some claims regarding limitations on the actions and behavior of the known third parties that it references. Such a site might wish to restrict its site-specific exceptions to only target domains for which those claims have been verified. (For example, consider the dilemma of a site that has trusted advertisers and analytics providers, along with some less trusted mashed-up content that might reference other sites). For this reason, site-specific exceptions can either be limited to a named set of target domains or be applicable to any target domain ("*").
It is expected that a site will explain to the user, in its online content, the need for an exception and the consequences of granting or denying that exception. Upon receipt of an informed consent from the user, a script operating on the site's page is expected to promise-call the Navigator.storeTrackingException API using parameters consistent with the consent granted by the user.
A site MUST ensure that a call to store an exception reflects the user's intention to grant an exception at the time of that call. It is the sole responsibility of the site to determine that a call to record an exception reflects the user's informed consent at the time of that call.
A first party site's page (the top-level browsing context) might be used to obtain site-specific consent for multiple parties; e.g., convey information about each party's policies and obtain specific consent for each party. In this case, the effective script origin might be different from the site for which consent is being granted. The scripting API allows for this but only for domains that are managed by the same data controller or a service provider acting for it. The user agent should check this by ensuring each domain either:
controller property
as that of the effective script origin, though this could involve
extra network round-trips.
Alternatively, a third party might encourage the user to visit their own site directly in order to engage in a consent dialog and make use of the API to store a web-wide exception. A web-wide exception can only be stored via the API when interacting with the web-wide target domain directly as a first party.
A site can request an exception be stored even when the user's general preference is not enabled. This permits the sending of DNT only for target resources for which an expressed preference is desired. Stored exceptions could affect which preference is transmitted if a user later chooses to configure a general tracking preference.
A user agent might not store the exception immediately, possibly because it is allowing the user to confirm. Even though the site has acquired the user's informed consent before calling the store API, it is possible that the user will change their mind, allow the storing of an exception to proceed but later remove it, or perhaps deny the storage by prior configuration. Nonetheless, at the time of a call, the site has acquired the user's consent and can proceed on that basis whether or not the user agent has stored an exception.
A site can promise-call the Navigator.trackingExceptionExists API to enquire whether an exception has been granted and stands in the user agent. If it resolves to false (the exception has expired, been deleted, or has not yet been stored), the user can be asked again for consent.
A user agent is expected to query the exceptions database at the time of a request in order to determine what value (if any) to send as the user's tracking preference.
A pair of duplets [A,B] and [X,Y] match if A matches X and B matches Y. A pair of values A and X match if and only if one of the following is true:
For example, a user might grant an exception for metrics.example.net
to track their activity on news.example.com and weather.example.com,
but not on medical.example.org. If the document at
http://news.example.com/news/story/2098373.html
has embedded references to
http://metrics.example.net/1x1.gif and
http://weather.example.com/widget.js, the
site domain for those references is
news.example.com and the target domains are
metrics.example.net and
weather.example.com, respectively.
A user agent MAY choose to disregard a user-granted exception when the target resource does not have a corresponding tracking status resource with a valid tracking status representation, since that would imply the target resource does not conform to this specification.
A site that stores exceptions is also expected to enable revocation of those exceptions. The Navigator.removeTrackingException API can be promise-called by a script to remove all exceptions applicable to that site.
A site MAY monitor for changes to its user-granted exceptions. If a user revokes consent by deleting an exception, the site MUST respect that revocation, though it MAY ask again for a new exception. In other words, a site MUST NOT resurrect a deleted exception without first interacting with and receiving new consent from the user.
When a site has obtained consent for a
user-granted exception, a script running within an active
browsing context of that site can promise-call
Navigator.storeTrackingException
to store one or more tracking exceptions.
A TrackingExData object is
supplied as a parameter to define the exception's scope (the set of
[site, target] duplets that encompass the granted exception)
and optional information to be stored for that exception.
The call returns a promise which either resolves to a
TrackingExResult or is rejected with
a DOMException identifying the reason for the failure.
A promise-call to Navigator.storeTrackingException from any
effective script origin other than that of the current
document.domain of the top-level browsing context's
active document [[!HTML5]] MUST be rejected with a DOMException
named "SecurityError".
partial interface Navigator {
Promise<TrackingExResult> storeTrackingException (
TrackingExData properties
);
};
dictionary TrackingExData {
sequence<DOMString>? sites;
sequence<DOMString>? targets;
DOMString? name;
DOMString? explanation;
DOMString? details;
long? maxAge;
};
dictionary TrackingExResult {
boolean isSiteWide;
};
Navigator.storeTrackingException passes a TrackingExData object. A user agent MUST ignore unknown properties of the TrackingExData object (for future extensibility). The following OPTIONAL properties are defined:
sites*.",
indicates any subdomain of the specified domain name.
If at least one of the selectors is equal to the
single character "*", the
exception is intended to be web-wide for the
single site domain, and every other selector is
then ignored. The array must only identify domains names
managed by the data controller of the designated resource,
or one of its service providers, and for this reason user
agents MUST reject the promise with a DOMException
named "SecurityError" if, for any selector in the list,
either:
same-party array
property of the site-wide tracking status resource
of the effective script origin.
targets[domain, *], meaning
that the exception applies to all domains referenced by each site.
[domain, domain] for each domain in
sites.
nameexplanationdetailsmaxAgemaxAge is supplied and not null, empty, or
negative, the user agent MUST remove the stored exception
no later than the specified number of seconds after being
stored.
maxAge is not supplied, the user agent
MAY retain the stored grant indefinitely.
Exceptions should only be granted where the referring domain is managed by the data controller of the site domain, or a service provider for it. The user agent MUST check this by ensuring each domain either:
The properties name, explanation, and details are provided by the caller for the sake of potential user interfaces. If a user agent presents these properties to the user, it ought to be clear that they are provided for informational value and are less important than the exception's technical effect.
In addition to the data above, a user agent might also store ambient information about the call, such as the URI associated with the top-level browsing context, the effective script origin, a current timestamp, or other information potentially obtained from applicable tracking status resources.
The calling site MUST have a site-wide tracking status resource with a valid tracking status representation that includes a policy property. This allows a user agent to obtain and possibly store additional information about the calling site’s controller and tracking policies at the time an exception is granted.
A user agent MAY reject the promise with a DOMException named "InvalidStateError" if it cannot determine the effective script origin or if the site corresponding to that origin does not have a site-wide tracking status resource with a valid tracking status representation.
For a site-specific exception,
a user agent MUST NOT store the duplets and MUST reject the
promise with a DOMException named "SecurityError"
if, for each domain in
sites,
the script's site domain would not be able to set a
cookie on it following the cookie domain rules [[!RFC6265]],
or if the domain is not referenced by the
same-party array
property of the site-wide tracking status resource
of the effective script origin
For example, a script on www.foo.bar.example.com can set one of the domains in
the sites as
"bar.example.com" or
"example.com", but not to com.
Similarly, tt cannot set a domain to "something.else.example.com",
unless that domain is also
referenced in the appropriate same-party property.
For any other failure, such as an incorrectly formatted parameter in the TrackingExData, the user agent MUST NOT store any of the target duplets in the database and MUST reject the promise with a DOMException named "SyntaxError".
Upon fulfillment, the user agent has added to its local database one or more site-pair duplets [site, target], each indicating that a request from that site domain to the target domain will include DNT:0 regardless of the user's general tracking preference. The fulfilled promise object contains the following TrackingExResult attribute:
isSiteWidetrue if the user agent stored a potentially
broader exception that applies to all domains (as opposed to just
the listed targets); otherwise, false.
When a list of targets
is supplied for a site-specific exception (i.e., other than when
sites contains a selector equal to "*",
the user agent MAY ignore that list, choosing instead to
store a site-specific exception for all domains
([site, *]), if it also indicates that result by
setting the returned promise's
isSiteWide property
to true.
User agents MAY instantiate Navigator.storeTrackingException even when Navigator.doNotTrack is null. Scripts SHOULD test for the existence of Navigator.storeTrackingException before calling the method.
There are some security concerns here regarding the ability of a
script with an effective script origin different from the
site being able to set site-specific exceptions that might impact
the behavior of that site. Likewise, it might be unwise for a script
to be able to impact the DNT values received by target domains when
the effective script origin differs from those targets.
However, a solution to these concerns would require additional
requests to verify that the effective script origin has the
right to set DNT for the given duplets, which is overkill given how
little value is obtained by setting the field without a legitimate
record of consent having been received.
This design is consistent with the fact that there is no technical
restraint from sites calling the API without having first obtained
an informed consent from the user. What we are assuming is that the
surrounding regulatory environment will be sufficient to punish
those who might misuse the API or abuse the scope of stored
exceptions.
When a site decides, or has been directed by the user, to revoke a
user-granted exception, a script running within an active
browsing context or nested browsing context of that
site can promise-call
Navigator.removeTrackingException
to remove one or more tracking exceptions.
A TrackingExData object is supplied as a
parameter to identify which exceptions are to be removed.
The call returns a promise which either resolves to
indicate success or is rejected with a DOMException
identifying the reason for the failure.
partial interface Navigator {
Promise<void> removeTrackingException (
TrackingExData properties
);
};
Navigator.removeTrackingException passes a TrackingExData object. A user agent MUST ignore unknown properties of the TrackingExData object (for future extensibility). The following OPTIONAL properties are defined:
A promise-call to Navigator.removeTrackingException from any
effective script origin other than that of the current
document.domain of the top-level browsing context's
active document [[!HTML5]] MUST be rejected with a DOMException
named "SecurityError".
*.",
indicates any subdomain of the specified domain name.
If at least one of the selectors is equal to the single
character "*",
the exceptions to be removed are web-wide for the
single site domain, and every other selector is
then ignored. The array must only identify domains names
managed by the data controller of the designated resource,
or one of its service providers, and for this reason user
agents MUST reject the promise with a DOMException
named "SecurityError" if, for any selector in the list,
either:
same-party array
property of the site-wide tracking status resource
of the effective script origin.
A user agent MUST NOT removethe duplets and MUST reject the
promise with a DOMException named "SecurityError"
if, for each domain in
sites,
the script's site domain would not be able to set a
cookie on it following the cookie domain rules [[!RFC6265]],
or if the domain is not referenced by the
same-party array
property of the site-wide tracking status resource
of the effective script origin
Any processing failure, such as an incorrectly formatted parameter in the TrackingExData, will result in no duplet being removed from the database of stored grants and the returned promise being rejected with a DOMException named "SyntaxError".
If there are no matching duplets in the database of stored grants when the method is called, this operation does nothing other than resolve the promise.
Upon fulfillment, the user agent MUST have removed any stored exceptions that matched the identified duplet(s).
When a site wishes to confirm that a user-granted exception
exists for a set of target domains potentially referenced by that
site, a script running within an active browsing context or
nested browsing context of that site can promise-call
Navigator.trackingExceptionExists with a
TrackingExData object supplied as a parameter that identifies
targets for which to confirm an exception exists.
The call returns a promise which either resolves to true or
false or is rejected with a DOMException
identifying the reason for the failure.
partial interface Navigator {
Promise<boolean> trackingExceptionExists (
TrackingExData properties
);
};
Navigator.trackingExceptionExists passes a TrackingExData object. A user agent MUST ignore unknown properties of the TrackingExData object (for future extensibility). The following OPTIONAL properties are defined:
A promise-call to Navigator.trackingExceptionExists from any
effective script origin other than that of the current
document.domain of the top-level browsing context's
active document [[!HTML5]] MUST be rejected with a DOMException
named "SecurityError".
[site, *] (an exception applicable to all
domains referenced by the site) is identified for matching
against the database of stored user-granted exceptions.
[site, domain] is identified for
matching against the database of stored
user-granted exceptions.
Any processing failure, such as an incorrectly formatted parameter in the TrackingExData, will result in the returned promise being rejected with a DOMException named "SyntaxError".
A user agent MUST fulfill the promise with the value
true if a current (non-expired) matching exception
exists for all of the duplets identified above, or
false if any of the identified duplets do not have a
matching exception.
Because the database might be changed at any time (via other windows or additional user interfaces), a particular response to the API might only be accurate at the time the promise is fulfilled.
There is no required user interface for a user agent regarding the granting of exceptions; a user agent MAY choose to provide none. Alternatively, a user agent MAY:
When an explicit list of target domains is provided through the API, their names might mean little to the user. The user might, for example, be told that there is a stored exception for a specific set of targets on such-and-such site, rather than listing them by name; or the user agent might decide to store an all-target exception, effectively ignoring any list of targets.
Conversely, if a wild-card is used for the target, the user might be told that there is a stored exception for all third parties that are embedded by the indicated site.
A user agent that chooses to highlight when tracking exceptions are applicable might provide an interface, such as a selectable icon in the status bar, that can direct the user to more information about the exception and how to revoke it.
In some user agent implementations, decisions to grant exceptions might have been made in the past (and since forgotten) or might have been made by other users of the device. Thus, exceptions might 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 might also desire to edit exceptions within a separate user interface, which would allow a user to modify their stored exceptions without visiting the target sites.
A user-agent MUST handle each set of exception duplets stored by a single storeTrackingException call as a 'unit', granting and maintaining the duplets in their entirety, or not at all. A user agent MUST NOT indicate to a site that it has stored an exception for targets {a, b, c} in the database, and later remove only one or two of {a, b, c} from its logical database of stored grants. This assures sites that the set of target domains they need for operational integrity is treated as a unit.
In addition to expressing the user's preference regarding tracking, this protocol enables servers to communicate machine-readable claims regarding their own tracking behavior. Since a personalized tracking status on every response would disable caching, a combination of response mechanisms are defined to allow the tracking status to be communicated prior to making a trackable request and without making every response dynamic.
A tracking status value (TSV) is a single character response to the user's tracking preference with regard to data collected via the designated resource. For a site-wide tracking status resource, the designated resource is any resource on the same origin server. For a Tk response header field, the target resource of the corresponding request is the designated resource, and remains so for any subsequent request-specific tracking status resource referred to by the Tk field value.
The tracking status value is case sensitive, as defined formally by the following ABNF.
TSV = %x21 ; "!" — under construction
/ %x3F ; "?" — dynamic
/ %x47 ; "G" — gateway to multiple parties
/ %x4E ; "N" — not tracking
/ %x54 ; "T" — tracking
/ %x43 ; "C" — tracking with consent
/ %x50 ; "P" — tracking only if consented
/ %x44 ; "D" — disregarding DNT
/ %x55 ; "U" — updated
/ TSV-extension
A tracking status value of ! means that the origin
server is currently testing its communication of tracking status.
The ! value has been provided to ease testing and
deployment on production systems during the initial periods of
testing compliance and during adjustment periods due to future
protocol changes or shifting regulatory constraints. Note that
this value does not indicate that the user's preference will be
ignored, nor that tracking will occur as a result of accessing
the designated resource.
A tracking status value of ? means the origin server
needs more information to determine tracking status, usually
because the designated resource dynamically adjusts
behavior based on information in a request.
If ? is present in the site-wide tracking status,
the origin server MUST send a Tk header field in all
responses to requests on the designated resource.
If ? 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 ? as the
tracking status value in the representation of a
request-specific tracking status resource.
A tracking status value of G means the server
is acting as a gateway to an exchange involving multiple parties.
This might occur if a response to the designated resource
involves an automated selection process, such as dynamic bidding,
where the party that is selected determines how the request data
will be treated with respect to an expressed tracking preference.
Similar to the ? value, the G TSV
indicates that the actual tracking status is dynamic and will be
provided in the response message's Tk header field,
presumably using information forwarded from the selected party.
This tracking status value is only valid as a site-wide status.
A server MUST NOT send G as the
tracking status value in a Tk header field or within the
representation of a request-specific tracking status resource.
If G is present in the site-wide tracking status:
With respect to tracking performed by the gateway itself, the
G response can be considered equivalent
to the T (tracking) response defined below.
The other information within the site-wide tracking status
representation indicates how the gateway intends to comply
with an expressed tracking preference, aside from the potential
sharing of data implied by the gateway process.
A tracking status value of N means the origin server
claims that data collected via the designated resource is
not used for tracking and will not be combined with other data in
a form that would enable tracking.
A tracking status value of T means the origin server
might perform or enable tracking using data collected via the
designated resource. Information provided in the tracking
status representation might indicate whether such tracking is
limited to a set of commonly accepted uses or adheres to one or
more compliance regimes.
A tracking status value of C means that the origin
server 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.
An origin server that sends the C tracking status
value for a designated resource MUST provide a reference
for controlling consent within the config
property of its corresponding tracking status representation
().
A tracking status value of P means that 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 forty-eight hours any DNT:1 data
received for which such consent has not been received.
Since this status value does not itself indicate whether a
specific request is tracked, an origin server that sends a
P tracking status value MUST provide a
config property in the corresponding tracking
status representation that links to a resource for obtaining
consent status.
The P tracking status value is specifically meant to
address audience survey systems for which determining consent at
the time of a request is either impractical, due to legacy systems
not being able to keep up with Web traffic, or potentially "gamed"
by first party sites if they can determine which of their users
have consented. The data cannot be used for the sake of
personalization. If consent can be determined at the time of a
request, the C tracking status is preferred.
A tracking status value of D means that the origin
server is unable or unwilling to respect a tracking preference
received from the requesting user agent. An origin server that
sends the D tracking status value MUST detail within
the server's corresponding privacy policy the conditions under
which a tracking preference might be disregarded.
For example, an origin server might disregard the DNT field received from specific user agents (or via specific network intermediaries) that are deemed to be non-conforming, might be collecting additional data from specific source network locations due to prior security incidents, or might be compelled to disregard certain DNT requests to comply with a local law, regulation, or order.
This specification is written with an assumption that the
D tracking status value would only be used in
situations that can be adequately described to users as an
exception to normal behavior. If this turns out not to be the
case, either the server's decision to send the D
signal needs re-examination, or this specification, or both.
A tracking status value of U means that 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.
Extensibility of the TSV set ensures that this protocol will continue to be usable as regional laws and regulatory environments evolve over time and compliance specifications are developed accordingly.
An origin server MAY send a TSV-extension character as a TSV if that extension has been defined by a future version of this specification or a compliance regime identified within the compliance property. Aside from storage or presentation of a server's response, a recipient MUST treat a TSV-extension value that it does not recognize as if the value was P (tracking only if consented).
TSV-extension = %x23-25 ; #$%
/ %x2A-3B ; *+,-./0-9:;
/ %x40-42 ; @AB
/ %x45-46 ; EF
/ %x48-4D ; HIJKLM
/ %x4F ; O
/ %x51-53 ; QRS
/ %x56-5A ; VWXYZ
/ %x5F ; _
/ %x61-7A ; a-z
The Tk response header field is a means for indicating
the tracking status that applied to the corresponding request.
An origin server is REQUIRED to send a Tk header
field if its site-wide tracking status value is ?
(dynamic) or G (gateway), or when an interactive change is
made to the tracking status and indicated by U (updated).
Tk-field-name = "Tk" Tk-field-value = TSV [ ";" status-id ]
The Tk field-value begins with a tracking status value
(),
optionally followed by a semicolon and a status-id
that refers 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:
Tk: N
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 resource, header
fields, data, etc.), the origin server can provide an additional
subtree of well-known resources corresponding to each of those
distinct tracking statuses. The status-id
portion of the Tk field-value indicates which specific
tracking status resource applies to the current request.
The status-id is case-sensitive.
status-id = 1*id-char id-char = ALPHA / DIGIT / "_" / "-" / "+" / "=" / "/"
For example, a response containing
Tk: T;fRx42
indicates that data collected via the target resource might be used for tracking and that an applicable tracking status representation can be obtained by performing a retrieval request on
/.well-known/dnt/fRx42
Note that the status-id is resolved relative
to the origin server of the current request. A retrieval request
targeting that URI can be redirected, if desired, to some other
server. The status-id has been intentionally limited
to a small set of characters to encourage use of short tokens
instead of potentially long, human-readable strings.
If a Tk field-value has a tracking status value of
? (dynamic), the origin server MUST
send a status-id in the field-value.
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 config property 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).
Tk: U
A site-wide tracking status resource provides information about the potential tracking behavior of resources located at that origin server. A site-wide tracking status resource has the well-known identifier
/.well-known/dnt/
relative to the origin server's URI [[RFC5785]].
An origin server that receives a valid GET request
targeting its site-wide tracking status resource MUST send 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. Failure to
provide access to such a representation implies that the
origin server does not implement this protocol.
The representation can be cached, as described
in .
See for examples of how tracking status resources can be used to discover support for this protocol.
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 resource, header fields, data, etc.), the origin server can provide an additional subtree of well-known resources corresponding to each of those distinct tracking statuses. The Tk response header field () can include a status-id to indicate which specific tracking status resource applies to the current request.
A tracking status resource space is defined by the following URI Template [[RFC6570]]:
/.well-known/dnt/{+status-id}
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
Tk: ?;ahoy
refers to the specific tracking status resource
/.well-known/dnt/ahoy
Resources within the request-specific tracking status resource space are represented using the same format as a site-wide tracking status resource.
When sending a request for the tracking status, a user agent SHOULD include any cookie data [[RFC6265]] (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.
An origin server MUST NOT retain tracking data regarding requests on the site-wide tracking status resource or within the tracking status resource space, regardless of the presence, absence, or value of a DNT header field, cookies, or any other information in the request. In addition, an origin server MUST NOT send Set-Cookie or Set-Cookie2 header fields in responses to those requests, including the responses to redirected tracking status requests, and MUST NOT send a response having 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.
If the tracking status is applicable to all users, regardless of the received DNT field-value and other data received via the request, then the origin server SHOULD mark the response as cacheable [[!RFC7234]] and assign 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 tracking status representation 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 users that have the same DNT field-value, the origin server MUST send a Vary header field that includes "DNT" in its field-value or 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 origin server MUST send 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 .
For each tracking status resource, an origin server MUST provide a
valid representation using the
application/tracking-status+json media type.
This media type consists of a status object
serialized as JSON [[!RFC7159]]. More information about the
application/tracking-status+json media type can be
found in .
A tracking status representation consists of a single status object containing properties that describe the tracking status applicable to the designated resource. Most of the properties are optional and can be extended over time, as illustrated by the following Orderly schema [[Orderly]]:
object {
string tracking; // TSV
array { string; } compliance?; // hrefs
string qualifiers?; // compliance flags
array { string; } controller?; // hrefs
array { string; } same-party?; // domains
array { string; } audit?; // hrefs
string policy?; // href
string config?; // href
}*;
The following example representation demonstrates a status object with all of the properties defined by this specification.
{
"tracking": "T",
"compliance": ["https://acme.example.org/tracking101"],
"qualifiers": "afc",
"controller": ["https://www.example.com/privacy"],
"same-party": [
"example.com",
"example_vids.net",
"example_stats.com"
],
"audit": [
"http://auditor.example.org/727073"
],
"policy": "/privacy.html#tracking",
"config": "http://example.com/your/data"
}
A status object MUST have a property named
tracking with a string value containing
the tracking status value
()
applicable to the designated resource.
For example, the following demonstrates a minimal tracking status representation that is applicable to any resource that does not perform tracking.
{"tracking": "N"}
An origin server MAY send a property named
compliance with an array value containing
a list of URI references that identify specific regimes to which
the origin server claims to comply for the designated resource.
Communicating such a claim of compliance is presumed to improve
transparency, which might influence a user's decisions or
configurations regarding allowed tracking.
If an origin server sends a TSV-extension or an
extension property in the status object
that is not defined by successors of this specification, the
origin server MUST send a compliance property that
contains a reference to the definitive specification of that
extension. If more than one reference in the compliance
array defines the same extension value, the origin server SHOULD
list the array of references in order by intended precedence.
An origin server MAY send a property named
qualifiers with a string value
containing a sequence of case sensitive characters corresponding
to explanations or limitations on the extent of tracking.
Multiple qualifiers indicate that multiple explanations or forms
of tracking might apply for the designated resource.
The meaning of each qualifier is presumed to be defined by one
or more of the regimes listed in compliance.
An origin server MAY send a property named
controller with an array value containing
a list of URI references indirectly identifying the party or
set of parties that claims to be the responsible data controller
for personal data collected via the designated resource. An origin
server MUST send a controller property if the
responsible data controller does not own the designated resource's
domain name.
An origin server that does not send controller
is implying that its domain owner is the sole data controller;
information about the data controller ought to be found on the
designated resource's site root page, or by way of a clearly
indicated link from that page (i.e., an absent controller property
is equivalent to: "controller":["/"]).
If the designated resource has joint data controllers
(i.e., multiple parties have independent control over the
collected data), the origin server MUST send a
controller property that contains a reference
for each data controller.
Each URI reference provided in controller ought to
refer to a resource that, if a retrieval action is performed on
that URI, would provide the user with information regarding (at a
minimum) the identity of the corresponding party and its data
collection practices.
Since a user's experience on a given site might be composed of
resources that are assembled from multiple domains, it might be
useful for a site to distinguish those domains that are subject to
their own control (i.e., share the same data controller as the
referring site).
An origin server MAY send a property named
same-party 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, if all data collected via those references share the
same data controller as the designated resource.
A user agent might use the same-party array,
when provided, to inform or enable different behavior for
references that are claimed to be same-party versus those for
which no claim is made. For example, a user agent might choose to
exclude, or perform additional pre-flight verification of,
requests to other domains that have not been claimed as same-party
by the referring site.
An origin server MAY send a property named
audit with an array value containing a
list of URI references to external audits of the designated
resource's privacy policy and tracking behavior.
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.
An origin server MAY send a property named
policy with a string value containing a
URI reference to a human-readable document that describes the
relevant privacy policy for the designated resource.
This document can inform users about data that might be collected
when the designated resource is accessed and how collection, use,
or sharing of such data might differ based on receipt of an
expressed tracking preference (DNT:1 or DNT:0).
An origin server MUST send a policy property if that
server is the effective script origin of a script that calls
the JavaScript API for storing a user-granted exception, as
described in
.
The content of such a policy document is beyond the
scope of this protocol and only supplemental to what is described
in the machine-readable tracking status representation.
If no policy property is provided, this
information might be obtained via the links provided in
controller.
If the policy associated with a designated resource happens to be defined as a common standard that is applicable to multiple sites, or includes such a standard by reference, that standard ought to be referenced by a URI within the machine-readable compliance property.
An origin server MAY send a property named
config with a string value containing a
URI reference to a resource for giving the user control over
personal data collected via the designated resource (and possibly
other resources).
If the tracking status value indicates prior consent
(C), the origin server MUST send a
config property referencing a resource that
describes how such consent is established and how to revoke that
consent.
A config 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 are
beyond the scope of this protocol.
If no config property is provided, this
information might be obtained via the links provided in
controller or policy.
Extensibility of the status object ensures that this protocol will continue to be usable as regional laws and regulatory environments evolve over time and compliance specifications are developed accordingly.
An origin server MAY send additional properties in the status object if those extensions have been defined by a future version of this specification or a compliance regime identified within the compliance property. Aside from storage or presentation of a server's response, a recipient MUST ignore extension properties that it does not recognize.
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 a 409 (Conflict) response with a message payload that describes why the request has been refused and how one might supply the required consent or exception to avoid this conflict [[!RFC7231]].
The 409 response ought to 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.
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.
Deployment of this protocol for a given service can
be discovered by making a retrieval request on the site-wide
tracking resource
relative
to the service URI.
/.well-known/dnt/
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.
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.
A user agent can 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 status object. If the retrieval is unsuccessful or parsing results in a syntax error, the user agent ought to consider the site to be non-conformant with this protocol.
The status object is supposed to have a
property named tracking containing the tracking
status value. The meaning of each tracking status value is defined
in .
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.
Information communicated via the DNT header field is minimized to avoid abuse of the field for fingerprinting or as a side-channel. However, future DNT-extensions might allow for the sending of additional information when signaling consent for tracking via DNT:0, since this consent mechanism is intended to be more persistent than cookies and could be used to convey a pseudonymous identifier as a user-preferred alternative to allowing a cookie to be set.
Use of client-side storage is always a security concern. Although the information being stored for each user-granted exception is limited and cannot be directly accessed by scripts, storing too many exceptions might exceed available storage or indicate an attempt to exploit other vulnerabilities.
There are also security concerns regarding the ability of scripts to store exceptions beyond the scope of their effective script origin. See the note about API security in .
This specification defines a protocol for communicating the user's
tracking preference, not a protocol that prevents tracking on its own.
It might be tempting to assume that design for privacy
would
justify calling for DNT:1 to be preconfigured as the default
for all user agents. However, that would violate the field's semantics,
make its presence in a request meaningless, and add eight extra bytes
to every HTTP request (with no effect).
The DNT signal alone does nothing to enhance a user's privacy. It is only when recipients believe that the signal has been deliberately and knowingly configured, and not defined as a default, that they will consider it to be the user's preference. Furthermore, when no signal is sent, recipients remain subject to whatever regulatory, legal, or other regional requirements regarding tracking exist in the absence of consent.
User-granted exceptions introduce a privacy risk. By storing client-side configurable state and providing functionality to learn about it later, the user-granted exceptions 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.
A database of stored exceptions is effectively storing a local history of the sites browsed by the user over time. Separate databases are needed per user profile (and per incognito session) and ought to be protected from observation. A user might wish to clear stored exceptions, or clear the database as a whole, but as a separate action from clearing the visible browser history.
This specification consists of input from many discussions within and around the W3C Tracking Protection Working Group, along with written contributions from Adrian Bateman (Microsoft), Justin Brookman (CDT), Nick Doty (W3C/MIT), Marcos Caceres (Mozilla), Rob van Eijk (Invited Expert), Roy T. Fielding (Adobe), Vinay Goel (Adobe), Tom Lowenthal (Mozilla), Jonathan Mayer (Stanford), Aleecia M. McDonald (Stanford), Mike O'Neill (Baycloud Systems), Matthias Schunter (Intel), John Simpson (Consumer Watchdog), David Singer (Apple), 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 JavaScript DOM property for doNotTrack 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.
The Internet media type application/tracking-status+json is used for tracking status representations ().