This document provides definitions, use cases, and requirements for making device APIs more privacy-friendly.
This document is expected to be further updated based on both Working Group input and public comments. The Working Group anticipates to eventually publish a stabilized version of this document as a W3C Working Group Note.


Privacy considerations are important to Device APIs, since misuse of information exposed by the APIs can have potentially harmful financial, physical safety, reputational and other impacts. Privacy needs a systemic solution that includes functional requirements on user agents, web sites and other components of the system, since any opportunity for misuse of private information is a risk. Addressing privacy may include functional requirements in technical standards, laws and regulations, and best practices.

While privacy is an important consideration for all APIs, privacy risks may vary according to the information exposed by an individual API. For example, inappropriate disclosure of contacts or location information could create serious personal safety issues in a broad range of cases, while disclosure of certain system information might create privacy risks in fewer contexts.

Architectural Approach

Privacy is a broad topic with various aspects that involve different parties in a system. In order to be clear which aspects are addressed and how, we take an architectural approach of breaking down the problem into smaller pieces. This should provide clarity and enable privacy-respecting solutions that can be adopted. We have identified the following pieces:

Defining APIs in such a way that they are as “naturally” privacy-respecting as possible

This is similar to writing APIs in such a way that they are security-friendly; you can't keep people from making mistakes, but you can make it easier and more natural to be privacy-respecting through the API design. An example is supporting the concept of Minimization by designing APIs that return the minimum data needed for a task, such as only obtaining address fields when an address is needed.

Requiring from user agents what they can realistically enforce

User agents are crucial to ensuring that user privacy is protected, but this capability must take implementation and adoption considerations into account. User agent design decisions can be separated to a large degree from API design decisions.

Empowering users to express privacy preferences

This can be hard to manage technically but might be possible through a simpler approach of defining and agreeing upon a small set of privacy preferences, similar to Creative Commons copyright licenses, that users can attach to their data. Defining a simple vocabulary for privacy could enable privacy rulesets that can be referenced by URI. Other people have had this idea as well.

Conducting education and outreach, similar to the accessibility efforts

WAI and the Web community at large have done a great job raising awareness about accessibility issues, and while implementations are not perfect, their effort has had a very measurable impact. There is therefore experience to be tapped in such an approach for the parts of the problem that depend on convincing people to do the right thing (which in some cases can be wide-ranging, including making script libraries support the solution directly, or having various organizations enforce it internally).

Privacy Principles relevant to APIs

Privacy protections are frequently understood as a set of principles or elements (one such set is described in [[PRIVACY-ISSUES-GEO]]). The core elements of privacy that are relevant to Device APIs, user agents that support the APIs, and applications that use the APIs are as follows:

These elements will each need to be approached in different ways. Approaches include specific requirements on individual APIs, conveying user expectations together with the data itself, and/or documenting best practices for application and content developers. Certain approaches are better suited to safeguarding certain privacy elements than others.

This document provides specific requirements for individual APIs, addressing the elements that are most relevant to API definitions: notice, consent, minimization, control, and access. Requirements involving user expectations, which primarily address retention, secondary use, and sharing, will be documented separately. Best practices for developers will also be documented separately, covering notice, minimization, control, access, retention, secondary use, and sharing in the application developer context.

The following table summarizes the breakdown of how each element is covered:

Privacy Element Requirements for API Definitions Requirements related to User Expectations of Data Use Best practices for developers
Notice X X
Consent X X
Minimization X X
Control X X
Access X X
Retention X X
Secondary Use X X
Sharing X X

The privacy requirements for individual APIs are provided in the next section. The requirements described in this document are intended to be applicable to device APIs both in the context of widgets and web applications.

The breakdown described above foreshadows the idea of providing API hooks that allow users to attach their expectations/preferences/policies about privacy to the data they share through the APIs. Attaching policy rules to the data that get shared can provide a legal basis for enhancing the control users have over their data once they are shared; but doing so create the following challenges:

Requirements for API Definitions

Many of the requirements listed here are recommendations (SHOULDs) rather than absolute requirements (MUSTs). In many cases this is because making a requirement absolute is appropriate for only a subset of the APIs, but not every API. As appropriate, individual APIs may place stronger normative requirements on user agents than the requirements in this document place on APIs.


Making sure that users understand the implications of using an application that relies on a Device API is fundamental to ensuring the protection of their data. The following requirements can help to make sure that users are properly notified:

Should the APIs have a hook for applications to convey the intended usage of the data? If they do, should it be a required parameter? And how can this information be conveyed without misleading the user about the trustworthiness of that information?


To reduce the risks of over-exposing users data, it is important to design APIs so that Web developers can request as little information as they need to accomplish their goals.

An example use case is a social networking case where the contacts API is used to contacts who are also members of a social network. Email addresses serve as the social network handles. In this case limiting results to the addresses and not other personal information is an example of minimization.

This gives rise to the following requirements:


Given the sensitivity of the data made available through Device APIs, it is important for users to be able to control which applications have access to that data. The following requirements ensure that (1) users have control over their data even after they have shared it with an application, and (2) users have robust controls over which applications can obtain their data to begin with:


Notice and control cannot be fully implemented unless users can review how they have shared data in the past. The following requirements suggest how APIs can support users’ access to this information:

Requirements related to User Expectations of Data Use

Users may have expectations of how their data is used, in particular related to data retention, use for other purposes, and sharing. How applications specify how they plan to meet these expectations (application policy), how users express their desires (user policy) and constraints on data use may all be related to managing these expectations. A license approach similar to Creative Commons may offer a simple manner to address these requirements.

This section does not currently contain any requirements. Because retention, secondary use, and sharing are largely out of the control of the APIs, it's not entirely clear that it makes sense to have any API requirements about these aspects. On the other hand, one can envision a requirement that supports the ruleset model, such as:

Likewise, if we wanted the APIs to support applications' ability to convey their intended policies about these aspects, we could have a requirement like:


Retention is about to user expectations about how long data they provide will be retained, and whether applications must dispose of collected data after fulfilling the purpose for which it was collected.

Secondary Use

Secondary Use is about to user expectations regarding whether applications can use data for purposes other than that for which the data was collected.


Sharing is about user expectations on how data will be shared. Once data have been made available to a requester, the requester is in a position to store and redistribute these data, with or without the user consent. Granularity of data shared is an important aspect of sharing.