This specification defines a JSON-based manifest that provides developers with a centralized place to put metadata associated with a web application. This includes, but is not limited to, the web application's name, links to icons, as well as the preferred URL to open when a user launches the web application. The manifest also allows developers to declare a default orientation for their web application, as well as providing the ability to set the display mode for the application (e.g., in fullscreen). Additionally, the manifest allows a developer to "scope" a web application to a URL. This restricts the URLs to which the manifest is applied and provides a means to "deep link" into a web application from other applications.

Using this metadata, user agents can provide developers with means to create user experiences that are more comparable to that of a native application.

To associate documents of a web application with a manifest, this specification defines the manifest link type as a declarative means for a document to be associated with a manifest (either directly in a HTML document or over the wire using [[RFC5988]]).

Implementors need to be aware that this specification is not stable. However, aspects of this specification are shipping in at least one browser (see links to implementation status at the top of this document). Implementors who are not taking part in the discussions will find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation phase should subscribe to the repository on GitHub and take part in the discussions.

Usage Examples

This section shows how developers can make use of the various features of this specification.

Example manifest

The following shows a typical manifest.

{
  "lang": "en",
  "name": "Super Racer 2000",
  "short_name": "Racer2K",
  "icons": [{
        "src": "icon/lowres",
        "sizes": "64x64",
        "type": "image/webp"
      }, {
        "src": "icon/hd_small",
        "sizes": "64x64"
      }, {
        "src": "icon/hd_hi",
        "sizes": "128x128",
        "density": 2
      }],
  "splash_screens": [{
        "src": "splash/lowres",
        "sizes": "320x240"
      }, {
        "src": "splash/hd_small",
        "sizes": "1334x750"
      }, {
        "src": "splash/hd_hi",
        "sizes": "1920x1080",
        "density": 3
      }],
  "scope": "/racer/",
  "start_url": "/racer/start.html",
  "display": "fullscreen",
  "orientation": "landscape",
  "theme_color": "aliceblue"
}

Using a link element to link to a manifest

Example of using a link element to associate a website with a manifest. The example also shows how to use [[!HTML]]'s link and meta elements to give the web application a fallback name and set of icons.

<!doctype>
<html>
<title>Store finder - search</title>

<!-- Startup configuration -->
<link rel="manifest" href="manifest.webmanifest">

<!-- Fallback application metadata for legacy browsers -->
<meta name="application-name" content="Store Finder">
<link rel="icon" sizes="16x16 32x32 48x48" href="lo_def.ico">
<link rel="icon" sizes="512x512" href="hi_def.png">

Installable web applications

This document attempts to address the Use Cases and Requirements for Installable Web Apps .

A web application is installed if the user agent has provided the end-user with a means of instantiating a new top-level browsing context that has the manifest's members applied to it. That is, the manifest's members, or their defaults, are in effect on the top-level browsing context (see application context).

An example of installing would be a user agent that allows the end-user to add a shortcut to a web application on their device's homescreen (using the name and one of the icons found in the manifest). Then, when the end-user launches a web application through this explicit means, the manifest is applied to the browsing context prior to the start URL being loaded. This gives the user agent time to apply the relevant values of the manifest, possibly changing the display mode and screen orientation of the web application.

Alternatively, an application context can be launched through a deep link (a URL that is within scope of the installed web application); in which case, the manifest is applied and the deep link is loaded within the context of web application.

Authority of the manifest's metadata

When a manifest is linked from a Document, it indicates to the user agent that the metadata is authoritative: that is, the user agent SHOULD use the metadata of the manifest instead of the one in the Document. However, in cases where metadata is missing, or in error, a user agent MAY fallback to the Document to find suitable replacements for missing manifest members (e.g., using application-name in place of short_name).

Installability signals

By design, this specification does not provide developers with an explicit API to "install" a web application. Instead, a manifest can serve as an installability signal to a user agent that a web application can be installed.

Examples of installability signals for a web application:

This list is not exhaustive and some installability signals might not apply to all user agents. How a user agent makes use of these installability signals to determine if a web application can be installed is left to implementers.

Navigation scope

A navigation scope is a [[!URL]] that represents the set of URLs to which an application context can be navigated while the manifest is applied. To determine if a URL is within the navigation scope, the user agent MUST run the within scope algorithm.

A string targetURL is said the be within scope of navigation scope scopeURL if the following algorithm returns true:

  1. If scopeURL is undefined (i.e., it is unbounded because of an error or it was not declared in the manifest), return true.
  2. Let target be a new URL using targetURL as input. If target is failure, return false.
  3. If target is same origin as scope and target's pathname starts with scope's pathname, return true.
  4. Otherwise, return false.

Enforcing the navigation scope depends on [[!HTML]]'s navigate algorithm. As such, the following algorithm monkey patches [[!HTML]]. Bug 27653 has been filed to address this.

The user agent MUST navigate the application context as per [[!HTML]]'s navigate algorithm with exceptions enabled. If the URL of the resource being loaded in the navigation is not within scope of the navigation scope, then the user agent MUST behave as if the application context is not allowed to navigate (this provides the ability for the user agent to perform the navigation in a different browsing context, or in a different user agent entirely). If during the handle redirects step of HTML's navigate algorithm the redirect URL is not within scope, abort HTML's navigation algorithm with a SecurityError.

A developer specifies the navigation scope via the scope member. In the case where the scope member is missing or in error, the navigation scope is treated as unbounded (represented as the value undefined). In such a case, the manifest is applied to all URLs the application context is navigated to (see related security considerations).

When the navigation scope is unbounded and a display mode other than browser is being applied, it is RECOMMENDED that user agents signal to the end-user when security and/or privacy sensitive navigations occur. The manner of signaling is left up to implementers, but can include things like showing the URL of the application context, dropping out of fullscreen to the browser display mode. Examples of security and/or privacy sensitive navigations include, but are not limited to:

This specification distinguishes between behavior in first-party and third-party contexts. In particular, if a scope member is declared in the manifest, it is not possible to navigate the top-level browsing context to somewhere outside the scope while the manifest is applied to the top-level browsing context. That's not to say that the web application cannot be navigated: just that the set of URLs to which the manifest applies is restricted by the navigation scope.

Deep links

A deep link is a URL that is within scope of an installed web application.

The concept of a deep link is useful in that it allows hyperlinking from one installed application to another. This can be from a native application to an installed web application (and possibly vice versa!). Theoretically, this can provide seamless context switching between native and web applications through standard hyperlinks. And in the case where a particular web application is not installed, the OS can just open the link in the user's preferred web browser.

Implementers are encouraged make such context switching obvious to the user, for example, by adhering to the human interface guidelines of the underlying platform with respect to application switching.

Display modes

A display mode represents how the web application is being presented within the context of an OS (e.g., in fullscreen, etc.). Display modes correspond to user interface (UI) metaphors and functionality in use on a given platform. The UI conventions of the display modes are purely advisory and implementers are free to interpret them how they best see fit.

Once a user agent applies a particular display mode to an application context, it becomes the default display mode for the top-level browsing context (i.e., it is used as the display mode when the window is navigated). The user agent MAY override the default display mode for security reasons (e.g., the top-level browsing context is navigated to another origin) and/or the user agent MAY provide the user with a means of switching to another display mode.

When the display member is missing, or if there is no valid display member, the user agent uses the browser display mode as the default display mode. As such, the user agent is REQUIRED to support the browser display mode.

Each display mode, except browser, has a fallback display mode, which is the display mode that the user agent can try to use if it doesn't support a particular display mode. If the user agent does support a fallback display mode, then it checks to see if it can use that display mode's fallback display mode. This creates a fallback chain, with the default display mode (browser) being the last item in the chain.

For example, Awesome Browser only supports the minimal-ui and browser display modes, but a developer declares that she wants fullscreen in the manifest. In this case, the user agent will first check if it supports fullscreen (it doesn't), so it falls back to standalone (which it also doesn't support), and ultimately falls back to minimal-ui.

The display modes values and their corresponding fallback display modes are as follows:

fullscreen
Opens the web application without any user agent chrome and takes up the entirety of the available display area.
The fallback display mode for fullscreen is standalone.
standalone
Opens the web application to look and feel like a standalone native application. This can include the application having a different window, its own icon in the application launcher, etc. In this mode, the user agent will exclude UI elements for controlling navigation, but can include other UI elements such as a status bar.
The fallback display mode for standalone is minimal-ui.
minimal-ui
This mode is similar to fullscreen, but provides the end-user with some means to access a minimal set of UI elements for controlling navigation (i.e., back, forward, reload, and perhaps some way of viewing the document's address). A user agent can include other platform specific UI elements, such as "share" and "print" buttons or whatever is customary on the platform and user agent.
The fallback display mode for minimal-ui is browser.
browser
Opens the web application using the platform-specific convention for opening hyperlinks in the user agent (e.g., in a browser tab or a new window).
The browser display mode doesn't have a fallback display mode (conforming user agents are required to support the browser display mode).

The fullscreen display mode is orthogonal to, and works independently of, the [[WHATWG-FULLSCREEN]] API. The fullscreen display mode affects the fullscreen state of the browser window, while the [[WHATWG-FULLSCREEN]] API operates on an element contained within the viewport. As such, a web application can have its display mode set to fullscreen, while document.fullScreenElement returns null, and fullscreenEnabled returns false.

The 'display-mode' media feature

The display-mode media feature represents, via a CSS media query [[!MEDIAQ]], the display mode of the web application. This media feature applies to the top-level browsing context and any child browsing contexts. Child browsing contexts reflect the display mode of the top-level browsing context.

A user agent MUST expose the 'display-mode' media feature irrespective of whether a manifest is being applied to a browsing context. For example, if the end-user puts the whole user agent into fullscreen, then the user agent would reflect this change to CSS and scripts via the 'display-mode' media feature.

Please note that the fullscreen display mode is not directly related to the CSS :fullscreen pseudo-class specified in the [[WHATWG-FULLSCREEN]] API. The :fullscreen pseudo-class matches exclusively when a [[!HTML]] element is put into the fullscreen element stack. However, a side effect of calling the requestFullscreen() method on an element using the [[WHATWG-FULLSCREEN]] API is that the browser window can enter a fullscreen mode at the OS-level. In such a case, both :fullscreen and (display-mode: fullscreen) will match.

On some platforms, it is possible for a user to put a browser window into fullscreen without the aid of the [[WHATWG-FULLSCREEN]] API. When this happens, the :fullscreen pseudo class will not match, but (display-mode: fullscreen) will match. This is exemplified in CSS code below.

/* applies when the window is fullscreen */
@media all and (display-mode: fullscreen) {
    ...
}

/* applies when an element goes fullscreen */
#game:fullsceen{
    ...
}
Value:
fullscreen | standalone | minimal-ui | browser
Applies to:
visual media types
Accepts min/max prefixes:
No

A user agent MUST reflect the applied display mode of the web application via a CSS media query [[!MEDIAQ]].

Examples

An example in CSS:

@media all and (display-mode: minimal-ui) {
  /* ... */
}
@media all and (display-mode: standalone) {
  /* ... */
}

Accessing the display-mode media feature in ECMAScript through matchMedia() of [[cssom-view]]:

const standalone = matchMedia( '(display-mode: standalone)' );

standalone.onchange = (e) => {
  /* handle changes to display mode */
}

if (standalone.matches) {
  /* do standalone things */
}

Security and privacy considerations

The 'display-mode' media feature allows an origin access to aspects of a user’s local computing environment and, together with the display member, allows an origin some measure of control over a user agent’s native UI: Through a CSS media query, a script can know the display mode of a web application. An attacker could, in such a case, exploit the fact that an application is being displayed in fullscreen to mimic the user interface of another application.

Furthermore, by neglecting to define a scope member in the manifest, it's possible to put a web application into a display mode that persists cross-origin (for legacy reasons, this is the default behavior). In case where the navigation scope is unbounded, it is left to the user agent to either stop applying the manifest when a cross-origin navigation occurs or to show some sort of security warning to the user.

Associating a resource with a manifest

A resource is said to be associated with a manifest if the resource representation, an HTML document, has a manifest link relationship.

Linking to a manifest

The manifest keyword can be used with a [[!HTML]] link element. This keyword creates an external resource link.

Link type Effect on... Brief description
link a and area
manifest External Resource not allowed Imports or links to a manifest.

The media type for a manifest serves as the default media type for resources associated with the manifest link type.

In cases where more than one link element with a manifest link type appears in a Document, the user agent uses the first link element in tree order and ignores all subsequent link element with a manifest link type (even if the first element was erroneous). See the steps for obtaining a manifest.

To obtain a manifest, the user agent MUST run the steps for obtaining a manifest. The appropriate time to obtain the manifest is left up to implementations. A user agent MAY opt to delay fetching a manifest until after the document and its other resources have been fully loaded (i.e., to not delay the availability of content and scripts required by the document).

A manifest is obtained and applied regardless of the media attribute of the link element matches the environment or not.

Manifest life-cycle

This section defines algorithms for obtaining, processing, and applying a manifest, and gives recommendations to implementers on how to react when the manifest is updated.

Obtaining a manifest

The steps for obtaining a manifest are given by the following algorithm. The algorithm, if successful, returns a processed manifest and the manifest URL; otherwise, it terminates prematurely and returns nothing. In the case of nothing being return, the user agent MUST ignore the manifest declaration. In running these steps, a user agent MUST NOT delay the load event.

  1. From the Document of the top-level browsing context, let manifest link be the first link element in tree order whose rel attribute contains the token manifest.
  2. If manifest link is null, terminate this algorithm.
  3. If manifest link's href attribute's value is the empty string, then abort these steps.
  4. Let manifest URL be the result of parsing the value of the href attribute, relative to the element's base URL. If parsing fails, then abort these steps.
  5. Let request be a new [[!FETCH]] request, whose URL is manifest URL, and whose context is "manifest".
  6. If the manifest link's crossOrigin attribute's value is 'use-credentials', then set request's credentials to 'include'.
  7. Await the result of performing a fetch with request, letting response be the result.
  8. If response is a network error, terminate this algorithm.
  9. Let manifest be the result of running the steps for processing a manifest with response's body as the text, manifest URL, and the URL that represents the address of the top-level browsing context.
  10. Return manifest and manifest URL.

Authors are encouraged to use the HTTP cache directives to explicitly cache the manifest. For example, the following response would cause a cached manifest to be used one year from the time the response is sent:

HTTP/1.1 200 OK
Cache-Control: max-age=31536000
Content-Type: application/manifest+json

{
  "lang": "en",
  "name": "Super Racer 2000",
  "start_url": "/start.html",
  "display": "fullscreen",
  "orientation": "landscape"
}

Content security policy

A user agent MUST support [[!CSP3]].

The manifest-src and default-src directives govern the origins from which a user agent can fetch a manifest. As with other directives, by default the manifest-src directive is *, meaning that a user agent can, [[!CORS]] permitting, fetch the manifest cross-domain. Remote origins (e.g., a CDN) wanting to host manifests for various web applications will need to include the appropriate [[!CORS]] response header in their HTTP response (e.g., Access-Control-Allow-Origin: https://example.com).

For a [[!HTML]] document, [[!CSP3]]'s manifest-src directive controls the sources from which a [[!HTML]] document can load a manifest from. The same CSP policy's img-src directive controls where the icon's images can be fetched from.

Processing the manifest

When instructed to issue a developer warning, the user agent MAY report the conformance violation to the developer in a user-agent-specific manner (e.g., report the problem in an error console), or MAY ignore the error and do nothing.

When instructed to ignore, the user agent MUST act as if whatever manifest, member, or value caused the condition is absent.

The following algorithm provides an extension point: other specifications that add new members to the manifest are encouraged to hook themselves into this specification at this point in the algorithm.

The steps for processing a manifest are given by the following algorithm. The algorithm takes a text string as an argument, which represents a manifest, and a URL manifest URL, which represents the location of the manifest, and a URL document URL. The output from inputting an JSON document into this algorithm is a processed manifest .

  1. Let parsed manifest be an empty object.
  2. Let manifest be the result of parsing text. If parsing throws an error:
    1. Issue a developer warning with any details pertaining to the JSON parsing error.
    2. Set manifest to be the result of parsing the string "{}".
  3. If Type(manifest) is not "object":
    1. Issue a developer warning that the manifest needs to be an object.
    2. Set manifest to be the result of parsing the string "{}".
  4. Extension point: process any proprietary and/or other supported members at this point in the algorithm.
  5. Let start URL of parsed manifest be the result of running the steps for processing the start_url member with manifest, manifest URL, and document URL as arguments.
  6. Let display mode of parsed manifest be the result of running the steps for processing the display member with manifest as the argument.
  7. Let orientation of parsed manifest be the result of running the steps for processing the orientation member with manifest and display mode as arguments.
  8. Let name of parsed manifest be the result of running the steps for processing the name member with manifest as the argument.
  9. Let language of parsed manifest be the result of running the steps for processing the lang member with manifest as the argument.
  10. Let short name of parsed manifest be the result of running the steps for processing the short_name member with manifest as the argument.
  11. Let icons of parsed manifest be the result of running the steps for processing an array of images with manifest, manifest URL, and "icons" as arguments.
  12. Let splash screens of parsed manifest be the result of running the steps for processing an array of images with manifest, manifest URL, and "splashscreen" as arguments.
  13. Let scope of parsed manifest be the result of running the steps for processing the scope member with manifest, manifest URL, document URL, start URL as arguments.
  14. Let related_applications of parsed manifest be the result of running the steps for processing the related_applications member with manifest as argument.
  15. Let prefer_related_applications of parsed manifest be the result of running the steps for processing the prefer_related_applications member with manifest as argument.
  16. Return parsed manifest.

Applying the manifest

A manifest is applied to a top-level browsing context, meaning that the members of the manifest are affecting the presentation or behavior of a browsing context.

A top-level browsing context that has a manifest applied to it is referred to as an application context.

If an application context is created as a result of the user agent being asked to navigate to a deep link, the user agent MUST immediately navigate to the deep link with replacement enabled. Otherwise, when the application context is created, the user agent MUST immediately navigate to the start URL with replacement enabled.

Please note that the start URL is not necessarily the value of the start_url member: the user or user agent could have changed it when the application was added to home-screen or otherwise bookmarked.

The appropriate time to apply a manifest is when the application context is created and before navigation to the start URL begins.

Updating the manifest

By using the manifest URL, a user agent MAY periodically check if the contents of a manifest has been modified (e.g., by honoring HTTP cache directives associated with the manifest or by checking for updates after the web application has been launched). In the event that the members of the manifest have been updated, as determined by running the steps for processing a manifest and seeing if anything has changed, the user agent MAY update the metadata corresponding to the web application (e.g., by replacing the name, icons, navigation scope, or whatever other data has been changed).

In addition, even if the manifest has not been modified, the user agents MAY periodically check if resources referenced from a manifest (e.g., the icons) have been modified by honoring HTTP cache directives. If any resources have been modified, the user agent MAY replace any stale resources.

To avoid one application masquerading as another, it is RECOMMENDED that users be made aware of any such updates using implementation or platform specific conventions.

Manifest and its members

A manifest is a JSON document that contains startup parameters and application defaults for when a web application is launched. A manifest consists of a top-level object that contains zero or more members. Each of the members are defined below, as well as how their values are processed.

Every manifest has an associated manifest URL, which the [[!URL]] from which the manifest was fetched.

lang member

The lang member is a language tag (string) that specifies the primary language for the values of the manifest's name and short_name members.

A language tag is a string that matches the production of a Language-Tag defined in the [[!BCP47]] specifications (see the IANA Language Subtag Registry for an authoritative list of possible values, see also the Maintenance Agency for ISO 3166 country codes). That is, a language range is composed of one or more subtags that are delimited by a U+002D HYPHEN-MINUS ("-"). For example, the 'en-AU' language range represents English as spoken in Australia, and 'fr-CA' represents French as spoken in Canada. Language tags that meet the validity criteria of [[!RFC5646]] section 2.2.9 that can be verified without reference to the IANA Language Subtag Registry are considered structurally valid.

The steps for processing the lang member is given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of manifest with argument "lang".
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Otherwise, Trim(value) and let tag be the result.
  4. If calling IsStructurallyValidLanguageTag with tag as the argument returns false, then:
    1. issue a developer warning that the value is invalid.
    2. Return undefined.
  5. Otherwise, return the result of calling the CanonicalizeLanguageTag abstract operation, passing tag as the argument.

name member

The name member is a string that represents the name of the web application as it is usually displayed to the user (e.g., amongst a list of other applications, or as a label for an icon).

The steps for processing the name member is given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of manifest with argument "name".
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Otherwise, Trim(value) and return the result.

short_name member

The short_name member is a string that represents a short version of the name of the web application. It is intended to be used where there is insufficient space to display the full name of the web application.

The steps for processing the short_name member is given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of manifest with argument "short_name".
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Otherwise, Trim(value) and return the result.

scope member

The scope member is a string that represents the navigation scope of this web application's application context.

The steps for processing the scope member is given by the following algorithm. The algorithm takes a manifest manifest, a URL manifest URL , a URL document URL, and a URL start URL . This algorithm returns a URL or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of the manifest with argument "scope".
  2. Let type be Type(value).
  3. If type is not "string" or value is the empty string, then:
    1. If type is not "undefined", issue a developer warning that the type is unsupported.
    2. Return undefined.
  4. Let scope URL be a new URL using value as input and manifest URL as the base URL.
  5. If scope URL is failure:
  6. If scope URL is not same origin as document URL:
    1. Issue a developer warning that the scope needs to be same-origin as Document of the application context.
    2. Return undefined.
  7. If start URL is not within scope of scope URL:
    1. Issue a developer warning that the start URL is not within scope of the navigation scope.
    2. Return undefined.
  8. Otherwise, return scope URL.

splash_screens member

The splash_screens member is an array of image objects that can serve as a loading screen for the web application. A splash screen indicates to the end user that a loading process is occurring (in effect, that the web application is being prepared by the user agent in the background). As the splash_screens member is an array of image objects, developers can use unique image objects definitions to target minimum screen resolutions and pixel densities.

This feature is primarily intended for user agents that take a perceptible amount of time to self-initialize (e.g., take longer than 200ms to be able to render content) - as such, it is OPTIONAL for a user agent to display a splash screen while the web application is being loaded. On launching a web application, if displaying a splash screen, the user agent MUST queue a post-load task on the Document of the start URL to remove the splashscreen, or, alternatively can follow platform conventions for how long a splash screen is displayed (e.g., a minimum of 1 second).

The splashscreen member is processed using the steps for processing an array of images.

icons member

The icons member is an array of image objects that can serve as iconic representations of the web application in various contexts. For example, they can be used to represent the web application amongst a list of other applications, or to integrate the web application with an OS's task switcher and/or system preferences.

The icons member is processed using the steps for processing an array of images.

If there are multiple equally appropriate icons in icons, a user agent MUST use the last one declared in order at the time that the user agent collected the list of icons. If the user agent tries to use an icon but that icon is determined, upon closer examination, to in fact be inappropriate (e.g. because its content type is unsupported), then the user agent MUST try the next-most-appropriate icon as determined by examining the image object's members.

In the following example, the developer has made the following choices about the icons associated with the web application:

  • The developer has included two icons at the same size, but in two different formats. One is explicitly marked as WebP through the type member. If the user agent doesn't support WebP, it falls back to the second icon of the same size (and density). The media type of this icon can then be either determined via a HTTP header, or can be sniffed by the user agent once the first few bytes of the icon are received.
  • The developer wants to use an SVG icon for devices with at least 2dppx as the display density and only when the available dimensions are at least 72px. She has found that the SVG file looks too blurry at small sizes, even on high-density screens. To deal with this problem, she's included an SVG icon that is only used when the dimensions are at least 72px and the pixel density is at least 2dppx. Otherwise, the user agent uses the ICO file (hd_hi.ico), which includes a gamut of icons individually tailored for small display sizes.
{
  "icons": [
      {
        "src": "icon/lowres.webp",
        "sizes": "48x48",
        "type": "image/webp"
      },{
        "src": "icon/lowres",
        "sizes": "48x48"
      },{
        "src": "icon/hd_hi.ico",
        "sizes": "72x72 96x96 128x128 256x256"
      },{
        "src": "icon/hd_hi.svg",
        "sizes": "72x72",
        "density": 2
      }]
 }

display member

The display member is a string, whose value is one of display modes values. The item represents the developer's preferred display mode for the web application. When the member is missing or erroneous, the user agent MUST use the fallback display mode.

The steps for processing the display member are given by the following algorithm. The algorithm takes a manifest manifest as an argument, and returns a string.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of manifest passing "display" as the argument.
  2. If Type(value) is not "string" or Trim(value) is not part of the display modes values:
    1. If Type(value) is not "undefined", issue a developer warning that the type is unsupported.
    2. If value is not part of the display modes values, issue a developer warning that the value is unsupported.
    3. Return the fallback display mode's value.
  3. Otherwise, Trim(value) and set value to be the result.
  4. If value is not a display mode that the user agent supports, set value to value's fallback display mode and re-run this step.
  5. Return value.

orientation member

The orientation member is a string that serves as the default orientation for all top-level browsing contexts of the web application. The possible values are those of the OrientationLockType enum defined in [[!SCREEN-ORIENTATION]].

If the user agent honors the value of the orientation member as the default orientation, then that serves as the default orientation for the life of the web application (unless overridden by some other means at runtime). This means that the user agent MUST return the orientation to the default orientation any time the orientation is unlocked [[!SCREEN-ORIENTATION]] or the top-level browsing context is navigated.

Although the specification relies on the [[!SCREEN-ORIENTATION]]'s OrientationLockType, it is OPTIONAL for a user agent to implement the [[!SCREEN-ORIENTATION]] API. Supporting the [[!SCREEN-ORIENTATION]] API is, of course, RECOMMENDED.

Certain UI/UX concerns and/or platform conventions will mean that some screen orientations and display modes cannot be used together . Which orientations and display modes cannot be used together is left to the discretion of implementers. For example, for some user agents, it might not make sense to change the default orientation of an application while in browser display mode.

Once the web application is running, other means can change the orientation of a top-level browsing context (such as via [[!SCREEN-ORIENTATION]] API).

The steps for processing the orientation member are given by the following algorithm. The algorithm takes a manifest manifest and display mode display mode as an argument, and returns a string.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of manifest with argument "orientation".
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", issue a developer warning that the type is not supported.
    2. Return the empty string.
  3. Otherwise, Trim(value) and set value to be the result.
  4. If value is not one of the OrientationLockType enum values, or value is unsupported by the user agent, or the value cannot be used together with display mode:
    1. Issue a developer warning.
    2. Return the empty string.
  5. Return value.

start_url member

The start_url member is a string that represents the start URL , which is URL that the developer would prefer the user agent load when the user launches the web application (e.g., when the user clicks on the icon of the web application from a device's application menu or homescreen).

The start_url member is purely advisory, and a user agent MAY ignore it or provide the end-user the choice not to make use of it. A user agent MAY also allow the end-user to modify the URL when, for instance, a bookmark for the web application is being created or any time thereafter.

The steps for processing the start_url member are given by the following algorithm. The algorithm takes a manifest manifest, a URL manifest URL , and a URL document URL. This algorithm returns a URL.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of the manifest with argument "start_url".
  2. Let type be Type(value).
  3. If type is not "string" or value is the empty string:
    1. If type is not "undefined", issue a developer warning that the type is unsupported.
    2. Return a new URL whose input is document URL.
  4. Let url be a new URL using value as input and manifest URL as the base URL.
  5. If url is failure:
  6. If url is not same origin as document URL:
    1. Issue a developer warning that the start_url needs to be same-origin as Document of the top-level browsing context.
    2. Return a new URL whose input is document URL.
  7. Otherwise, return url.

For example, if the value of start_url is ../start_point.html, and the manifest's URL is https://example.com/resources/manifest.webmanifest, then the result of URL parsing would be https://example.com/start_point.html.

theme_color member

This feature is at risk of being removed from the spec. We are asking people interested in this feature to provide use cases for it. If you have any feedback, please comment on issue #356 - What's the use case for theme_color? on GitHub.

The theme_color member serves as the default theme color for an application context. What constitutes a theme color is defined in [[!META-THEME-COLOR]].

If the user agent honors the value of the theme_color member as the default theme color, then that color serves as the theme color for all browsing contexts to which the manifest is applied. However, a document may override the default theme color through the inclusion of a [[!HTML]] meta element that conforms to [[!META-THEME-COLOR]]. A user agent MUST return the theme color to the default theme color when there are no meta elements that conform to [[!META-THEME-COLOR]] in a document, or the top-level browsing context is navigated to a URL that is within scope.

The steps for processing the theme_color member are given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of manifest with argument "theme_color".
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Otherwise, let potential color be the result of running [[!CSS-SYNTAX-3]]'s parse a component value algorithm with value as input. If parsing returns a syntax error, return undefined.
  4. Let color be the result of attempting to parse potential color as a CSS color, as per [[!CSS-SYNTAX-3]]. If parsing fails:
    1. Issue a developer warning.
    2. Return undefined.
  5. Return color.

related_applications member

A related application is an application accessible to the underlying application platform that has a relationship with the web application associated with a manifest.

The related_applications member lists related applications and serves as an indication of such a relationship between web application and related applications. This relationship is unidirectional and unless a listed application claims the same relationship, the user agent MUST NOT assume a bi-directional endorsement.

Example of usages of the related_applications could be a crawler that would use that information to gather more information about the web application or a browser that could suggest a listed application as an alternative if the user wants to install the web application.

The steps for processing the related_applications member are given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a list of application objects applications, which can be empty.

  1. Let applications be an empty list.
  2. Let unprocessed applications be the result of calling the [[\GetOwnProperty]] internal method of manifest with argument "related_applications".
  3. If unprocessed applications is an array, then:
    1. For each potential application in the array:
      1. Let platform be the result of running the steps for processing the platform member of an application with potential application.
      2. If platform is undefined, move onto the next item if any are left.
      3. Let id be the result of running the steps for processing the id member of an application with potential application.
      4. Let url be the result of running the steps for processing the url member of an application with potential application.
      5. If both id and url are undefined, move onto the next item if any are left.
      6. Otherwise, let application be an object with properties platform, id, url respectively set to platform, id and url.
      7. Append application to applications.
  4. Otherwise, if unprocessed applications is not undefined:
    1. Issue a developer warning that the type is not supported.
  5. Return applications.

prefer_related_applications member

The prefer_related_applications member is a boolean value that is used as a hint for the user agent to say that related applications should be preferred over the web application. The user agent MUST consider the missing value as equivalent to have it set to false. If the prefer_related_applications is set to true, and the user agent wants to suggest to install the web application, the user agent might want to suggest installing one of the related applications instead.

The steps for processing the prefer_related_applications member are given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a boolean.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of manifest with argument "prefer_related_applications".
  2. If Type(value) is not "boolean":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return false.
  3. Return value.

Image object and its members

Each image object represents an image that is used as part of a web application, suitable to use in various contexts depending on the semantics of the member that is using the object (e.g., an icon that is part of an application menu, a splashscreen, etc.). For an image object, this specification provides developers with a means of specifying the dimensions, optimal pixel density, and media type of an image (i.e., a "responsive image" solution [[respimg-usecases]]). A user agent can use these values to select an image that is best suited to display on the end-user's device or most closely matches the end-user's preferences.

Content security policy of image objects

The security policy that governs whether a user agent can fetch an icon image is governed by the img-src directive [[!CSP3]] associated with the manifest's owner Document.

For example, given the following img-src directive in the Content-Security-Policy HTTP header of the manifest's owner Document:

HTTP/1.1 200 OK
Content-Type: text/html
Content-Security-Policy: img-src icons.example.com

<!doctype>
<html>
<link rel="manifest" href="manifest.webmanifest">


And given the following manifest.webmanifest:

{
    "name": "custom manifest",
    "start_url": "http://boo",
    "icons": [{
        "src": "//icons.example.com/lowres"
      },
      {
        "src": "//other.com/hi-res"
      }]
}

The fetching of icon resources from icons.example.com/lowres would succeed, while fetching from other.com/hi-res would fail.

background_color member

The background_color member of an image object is a color, expressed as a [[!CSS3-Color]] value, that represents a color on which a user agent SHOULD render an image object. For example, this color can be used when the dimensions of the display context exceeds those of the image object - and/or when the image contains transparent regions.

The steps for processing the background_color member of an image are given by the following algorithm. The algorithm takes an image object as an argument, and returns either a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of image with argument "background_color".
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Otherwise, let potential color be the result of running [[!CSS-SYNTAX-3]]'s parse a component value algorithm with value as input. If parsing returns a syntax error, return undefined.
  4. Let color be the result of attempting to parse potential color as a CSS color, as per [[!CSS-SYNTAX-3]]. If parsing fails:
    1. Issue a developer warning.
    2. Return undefined.
  5. Return color.

density member

The density member of an image object is the device pixel density for which this image was designed. The device pixel density is expressed as the number of dots per 'px' unit (equivalent to a dppx as defined in [[css3-values]]). The value is a positive number greater than 0. If the developer omits the value, the user agent assumes the value 1.0.

The steps for processing a density member of an image are given by the following algorithm. The algorithm takes an image image object as an argument and returns a positive number.

  1. If [[\HasOwnProperty]] internal method of image passing density as the argument returns false:
    1. Return 1.0.
  2. Let value be the result of calling the [[\GetOwnProperty]] internal method of image passing " density" as the argument.
  3. Let result be the result of parseFloat( value);
  4. If result is NaN, +∞, or less than or equal to +0, then:
    1. Issue a developer warning.
    2. Return 1.0.
  5. Return result.

sizes member

The sizes member of an image object is a string consisting of an unordered set of unique space-separated tokens which are ASCII case-insensitive that represents the dimensions of an image. Each keyword is either an ASCII case-insensitive match for the string "any", or a value that consists of two valid non-negative integers that do not have a leading U+0030 DIGIT ZERO (0) character and that are separated by a single U+0078 LATIN SMALL LETTER X or U+0058 LATIN CAPITAL LETTER X character. The keywords represent icon sizes in raw pixels (as opposed to CSS pixels). When multiple image objects are available, a user agent MAY use the value to decide which icon is most suitable for a display context (and ignore any that are inappropriate).

The steps for processing a sizes member of an image are given by the following algorithm. The algorithm takes an image object image. This algorithm will return a set.

  1. Let sizes be an empty set.
  2. Let value be the result of calling the [[\GetOwnProperty]] internal method of image passing " sizes" as the argument.
  3. Let type be Type(value).
  4. If type is not "string", then:
    1. If type is not "undefined", issue a developer warning that the type is unsupported.
    2. Return undefined.
  5. Otherwise, parse value as if it was a [[!HTML]] sizes attribute and let keywords be the result.
  6. For each keyword in keywords:
    1. Convert keyword to ASCII lowercase and add the resulting string to sizes.
  7. Return sizes.

src member

The src member of an image object is a URL from which a user agent can fetch the image's data.

The steps for processing the src member of an image are given by the following algorithm. The algorithm takes a image object icon, and a URL manifest URL , which is the URL from which the manifest was fetched. This algorithm will return a URL or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of image passing " src" as the argument.
  2. Let type be Type(value).
  3. If type is not "string", then:
    1. If type is not "undefined", issue a developer warning that the type is unsupported.
    2. Return undefined.
  4. If Trim(value) is the empty string, then return undefined.
  5. Otherwise, parse value using manifest URL as the base URL and return the result.

type member

The type member of an image object is a hint as to the media type of the image. The purpose of this member is to allow a user agent to ignore images of media types it does not support.

There is no default MIME type for image objects. However, for the purposes of determining the type of the resource, user agents must expect the resource to be an image.

The steps for processing the type member of an image are given by the following algorithm. The algorithm takes an image object as an argument, and returns either a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of potential image passing "type" as the argument.
  2. Let type be Type(value).
  3. If type is not "string", then:
    1. If type is not "undefined", issue a developer warning that the type is unsupported.
    2. Return undefined.
  4. Trim(value) and set value to be resulting string.
  5. If value is not a valid MIME type or the value of type is not a supported media format, issue a developer warning and return undefined.
  6. Return value.

Processing an array of images

The steps for processing an array of images are given by the following algorithm. The algorithm takes a manifest, a URL manifest URL, which is the URL from which the manifest was fetched, and a string that represents the member name of the member which contains the array of image objects. This algorithm returns a list of image objects, which can be empty.

  1. Let images be an empty list.
  2. Let unprocessed images be the result of calling the [[\GetOwnProperty]] internal method of manifest with member name as the argument.
  3. If unprocessed images is an array, then:
    1. From unprocessed images, filter out any item where HasOwnProperty(item,"src") returns false.
    2. For each potential image in the array:
      1. Let src be the result of running the steps for processing the src member of an image with potential image and manifest URL.
      2. If src is undefined, move onto the next item in images (if any are left).
      3. Otherwise, let image be an object with properties src, type, sizes, and density. All properties initially set to undefined.
      4. Set image's src property to be src.
      5. Let type be the result of running the steps for processing the type member of an image passing potential image.
      6. If type is not undefined, set image's type property to be type.
      7. Let sizes be the list that result from running the steps for processing a sizes member of an image passing potential image.
      8. If sizes is not undefined, set image's sizes property to be sizes.
      9. Let density be the result from running the steps for processing a density member of an image are given by the passing potential image .
      10. If density is not undefined, set image's density property to be value.
      11. Append image to images.
  4. Otherwise, if unprocessed images is not undefined:
    1. Issue a developer warning that the type is not supported.
  5. Return images.

Application object and its members

Each application object represents an application related to the web application. An application object has three properties: a platform which represents the platform it is associated to, a url which represents the URL where the application can be found and an id which can be used as an information additional to the URL or instead of the URL, depending on the platform. A valid application object MUST have platform and either an url or an id (or both).

In the following example, the web application is listing two different related applications, one on Google Play Store and the other one on the iTunes Store:

{
  "related_applications": [
      {
        "platform": "play",
        "url": "https://play.google.com/store/apps/details?id=com.example.app1",
        "id": "com.example.app1"
      }, {
        "platform": "itunes",
        "url": "https://itunes.apple.com/app/example-app1/id123456789",
      }]
 }

Where should the platform expected value be listed?

platform member

The platform member of an application object represents the platform on which the application can be found.

The steps for processing the platform member of an application are given by the following algorithm. The algorithm takes an application object application. This algorithm will return a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of application passing "platform" as the argument.
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Otherwise, Trim(value) and return the result.

url member

The url member of an application object represents the url at which the application can be found.

The steps for processing the url member of an application are given by the following algorithm. The algorithm takes an application object application. This algorithm will return an URL or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of application passing "url" as the argument.
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Trim(value) and set value to be resulting string.
  4. Otherwise, parse value and if the result is not failure, return the result, otherwise return undefined.

id member

The id member of an application object represents the id which is used to represent the application on the platform.

The steps for processing the id member of an application are given by the following algorithm. The algorithm takes an application object application. This algorithm will return a string or undefined.

  1. Let value be the result of calling the [[\GetOwnProperty]] internal method of application passing "id" as the argument.
  2. If Type(value) is not "string":
    1. If Type(value) is not "undefined", optionally issue a developer warning that the type is not supported.
    2. Return undefined.
  3. Otherwise, Trim(value) and return the result.

Common conventions and dependencies

The [[\GetOwnProperty]] operation and the abstract operation hasOwnProperty , parseFloat(string) function, and the Type(x) notation are defined in [[!ECMASCRIPT]].

When instructed to Trim(x), a user agent MUST behave as if [[!ECMASCRIPT]]'s String.prototype.trim() function had been called on the string x.

As the manifest uses the JSON format, this specification relies on the types defined in [[!ECMA-404]] specification: namely object, array, number, string, true, false, and null. Strict type checking is not enforced by this specification. Instead, each member's definition specifies the steps required to process a particular member and what to do when a type does not match what is expected.

The URL concept and URL parsing are defined in [[!WHATWG-URL]].

The default orientation concept and the OrientationLockType enum, are defined in [[!SCREEN-ORIENTATION]].

The algorithm to parse a component value is defined in [[!CSS-SYNTAX-3]].

The manifest-src, img-src, and default-src directives are defined in [[!CSP3]].

The IsStructurallyValidLanguageTag and CanonicalizeLanguageTag abstract operations are defined in [[!ECMAS-402]].

The following are defined in [[!FETCH]]:

The following are defined in [[!HTML]]:

IANA considerations

The following registrations are for community review and will be submitted to the IESG for review, approval, and registration with IANA.

Media type registration

This section contains the required text for MIME media type registration with IANA.

The media type for a manifest is application/manifest+json.

If the protocol over which the manifest is transferred supports the [[!MIME-TYPES]] specification (e.g. HTTP), it is RECOMMENDED that the manifest be labeled with the media type for a manifest.

Type name:
application
Subtype name:
manifest+json
Required parameters:
N/A
Optional parameters:
N/A
Encoding considerations:
Same as for application/json
Security and privacy considerations:

This specification does not directly deal with high-value data. However, installed web applications and their data could be seen as "high value" (particularly from a privacy perspective).

As the manifest format is JSON and will commonly be encoded using [[!UNICODE]], the security considerations described in [[!ECMA-404]] and [[!UNICODE-SECURITY]] apply. In addition, because there is no way to prevent developers from including custom/unrestrained data in a manifest, implementors need to impose their own implementation-specific limits on the values of otherwise unconstrained member types, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.

Web applications will generally contain ECMAScript, HTML, CSS files, and other media, which are executed in a sand-boxed environment. As such, implementors need to be aware of the security implications for the types they support. Specifically, implementors need to consider the security implications outlined in at least the following specifications: [[!CSS-MIME]], [[!ECMAScript-MIME]], [[!HTML]].

As web applications can contain content that is able to simultaneously interact with the local device and a remote host, implementors need to consider the privacy implications resulting from exposing private information to a remote host. Mitigation and in-depth defensive measures are an implementation responsibility and not prescribed by this specification. However, in designing these measures, implementors are advised to enable user awareness of information sharing, and to provide easy access to interfaces that enable revocation of permissions.

As this specification allows for the declaration of URLs within certain members of a manifest, implementors need to consider the security considerations discussed in the [[!WHATWG-URL]] specification. Implementations intending to display IRIs and IDNA addresses found in the manifest are strongly encouraged to follow the security advice given in [[!UNICODE-SECURITY]].

Developers need to be aware of the security considerations discussed throughout the [[!CSP3]] specification, particularly in relation to making data: a valid source for the purpose of inlining a manifest. Doing so can enable XSS attacks by allowing a manifest to be included directly in the document itself; this is best avoided completely.

Applications that use this media type:
Web browsers
Additional information:
Magic number(s):
N/A
File extension(s):
.webmanifest
Macintosh file type code(s):
TEXT
Person & email address to contact for further information:
The Web Applications (WebApps) Working Group can be contacted at public-webapps@w3.org.
Intended usage:
COMMON
Restrictions on usage:
none
Author:
W3C's Web Applications (WebApps) Working Group.
Change controller:
W3C.

Link relation type registration

A request to register the manifest link relation type been submitted to IANA.

Relation Name:
manifest
Description:
Links to a manifest. A manifest provides developers with a centralized place to put metadata associated with a web application.
Reference:
http://www.w3.org/TR/appmanifest/
Notes:
Please refer to the steps for obtaining a manifest for details about how to fetch and apply a manifest.

There is only one class of product that can claim conformance to this specification: a user agent.

Although this specification is primarily targeted at web browsers, it is feasible that other software could also implement this specification in a conforming manner. For instance, search engines, or crawlers, could find and process manifests to build up catalogs of sites that potentially work as installable web applications.

Extensibility

This specification is designed to be extensible. Other specifications are encouraged to define new members for the manifest. However, in doing so, please follow the conventions used in this specification. In particular, use the extension point to hook into the steps for processing a manifest. Also, be sure to specify the steps for processing your particular member in the manner set forth in this specification. This will help keep this part of the platform consistent.

When specifying a new member, don't override or monkey patch anything defined in this specification. Also, don't assume your member will be processed before or after any other member. Keep your new member, and its processing, atomic and self contained. Note also that implementations are free to ignore any member they do not recognize or support.

If you are writing a specification and temporarily want to patch this specification to help implementations along, file a bug so the community is informed of what you are trying to do.

Proprietary manifest members

Although proprietary extensions are undesirable, they can't realistically be avoided. As such, the RECOMMENDED way to add a new proprietary manifest member as an extension is to use a vendor prefix.

The following is an example of two hypothetical vendor extensions.

  {
    ...
    "webkit_fancy_feature": "some/url/img",
    "moz_awesome_thing": { ... }
    ...
  }

Relationship to HTML's link and meta elements

An extensive discussion of why we chose to use JSON instead of HTML meta/link tags for this specification is available on GitHub and on the www-tag list. Below is a short summary of the key points raised in those discussions.

The document format defined in this specification provides a unified means of encapsulating metadata about a Web application in a way that we hope will avoid existing pitfalls with both proprietary and [[!HTML]]'s meta/link tags. Those pitfalls include:

Although it would be unrealistic to think that this specification won't bring its own set of problems, externalizing this data in the form of a manifest solves the problems described above. These problems are solved by:

In addition, standardizing the functionality currently provided by the various meta tag-based solutions within the manifest solves the problem of having to declare large number of proprietary and standard [[!HTML]] tags that all achieve the same thing. Of course, this hinges on the standard actually getting implemented by browsers and those browsers getting widely deployed to users: if this happens, the Web community might be able to retire many of the proprietary meta tags plaguing the Web at the time of writing. More information about the proprietary tags can be found in the Use Cases and Requirements for Installable Web Apps .

Lastly, this specification does not make the standardized solutions found in [[!HTML]] redundant. When members like the name or icons is missing from the manifest, user agents can search in a manifest's owner [[!HTML]] document for things like icons and the application name (or a user agent might even fallback to proprietary tags/metadata, if they are present in a document).

JSON Schema

Developers interested in validating manifest documents can find an unofficial JSON schema for the manifest format at schemastore.org. It is licensed under Apache 2.0. It is kindly maintained by Mads Kristensen. If you find any issues with the JSON schema, please file a bug at the SchemaStore repository on GitHub.

Acknowledgments

This document reuses text from the [[!HTML]] specification, edited by Ian Hickson, as permitted by the license of that specification.