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Web App Manifest | What is Manifest JSON?
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This specification defines a JSON-based manifest file that provides developers with a centralized place to put metadata associated with a web application. This metadata 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.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.
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.
This document was published by the Web Platform Working Group as a Working Draft . This document is intended to become a W3C Recommendation.
Comments regarding this document are welcome. Please send them to public-webapps @w3.org (archives) .
Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
This document was produced by a group operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
This document is governed by the 1 March 2019 W3C Process Document.
This section is non-normative.
This section shows how developers can make use of the various features of this specification.
This section is non-normative.
The following shows a typical manifest.
{
"lang": "en",
"dir": "ltr",
"name": "Super Racer 2000",
"description": "The ultimate futuristic racing game from the future!",
"short_name": "Racer2K",
"icons": [{
"src": "icon/lowres.webp",
"sizes": "64x64",
"type": "image/webp"
},{
"src": "icon/lowres.png",
"sizes": "64x64"
}, {
"src": "icon/hd_hi",
"sizes": "128x128"
}],
"scope": "/racer/",
"start_url": "/racer/start.html",
"display": "fullscreen",
"orientation": "landscape",
"theme_color": "aliceblue",
"background_color": "red"
}
link element to link to a manifestThis section is non-normative.
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>Super Racer 2000</title>
<!-- Startup configuration -->
<link rel="manifest" href="manifest.webmanifest">
<!-- Fallback application metadata for legacy browsers -->
<meta name="application-name" content="Racer2K">
<link rel="icon" sizes="16x16 32x32 48x48" href="lo_def.ico">
<link rel="icon" sizes="512x512" href="hi_def.png">
A common use case of a manifest is for a user agent to install a web application; whereby the user agent provides 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. This distinguishes an installed web application from a traditional bookmark, as opening a web page from a traditional bookmark will not have the manifest's properties applied to it.
For example, on user agents that support installation, a web application could be presented and launched in a way that, to the end-user, is indistinguishable from native applications: such as appearing as a labeled icon on the home screen, launcher, or start menu. When launched, the manifest is applied by the user agent to the top-level 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, and again as an example, the user agent could install the web application into a list of bookmarks within the user agent itself.
An end-user can manually trigger the installation process through the browser's UI. Alternatively, the installation process can occur through an automated install prompt: that is, a UI that the user agent presents to the user when, for instance, there are sufficient installability signals to warrant installation of the web application.
The application's name is derived from either the name member or short_name member (if either is present) - otherwise, it is generated by the user agent or provided by the end-user.
When either member is missing from the manifest, a user agent MAY use the name member as a fallback for the short_name member or vice versa.
If the name and short_name members are undefined, the user agent SHOULD assign a default name (e.g., "Untitled"). Alternatively, a user agent MAY allow the end-user to input some text that can serve as the application's name.
When both the name and short_name members are present, it is left up to implementations to decide which member is best suited for the space available (e.g., the short_name member might be better suited for the space available underneath an icon).
An installation process is an attempt by the user agent to install a web application. The details of such a process (i.e., the display of an install UI, and any resulting IO operations of the host OS) are left up to implementers. Implementers need to be aware that there are privacy and security considerations that directly relate to the installation process.
For the purpose of this specification, the installation succeeded once the installation process succeeds in installing the web application (e.g., an icon was successfully placed onto the device's homescreen). If the end-user cancels the installation process (even if they manually triggered it, and then changed their minds), then the installation was canceled. Otherwise, the installation failed. Reasons for installation failure can include, for example, the OS denying permission to the user agent to add an icon to the homescreen of the device and the end-user rejecting the installation.
The steps to install the web application are given by the following algorithm:
Window object of the top-level browsing context for which the user agent will attempt installation.Document's metadata to create an installation process.install at the window object.In the case that the end-user manually triggered the installation process, the user agent MUST run the steps to install the web application.
During the installation process, it is RECOMMENDED that the user agent allow the user to inspect the icon, name, start URL, origin, etc. pertaining to a web application. This is to give a user an opportunity to make a conscious decision about to approve, and possibly modify, the information pertaining to the web application before installing it. This also gives the user an opportunity to see if the user agent is spoofing another web application, by, for example, using an unexpected icon or name.
It is RECOMMENDED that user agents prevent other applications from determining which applications are installed on the system (e.g., via a timing attack on the user agent's cache). This could be done by, for example, invalidating from the user agent's cache the resources linked to from the manifest (for example, icons) after a web application is installed - or by using an entirely different cache from that used for regular web browsing.
This section is non-normative.
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:
name member and a suitable icon.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.
AppInstallEventHandlers mixinThe AppInstallEventHandlers mixin defines the event handler attributes on which events relating to the installation of a web application are fired.
[NoInterfaceObject, exposed=(Window)]
interface AppInstallEventHandlers {
attribute EventHandler oninstall;
};
Window implements AppInstallEventHandlers;
This example shows two ways of handling the install event.
function handleInstall(ev){
const date = new Date(ev.timeStamp / 1000);
console.log(`Yay! Our app got installed at ${date.toTimeString()}`);
}
// Using the event handler IDL attribute
window.oninstall = handleInstall;
// Using .addEventListener()
window.addEventListener("install", handleInstall);
oninstall attributeoninstall is an event handler IDL attribute for the "install" event type.
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 is standalone.standalone is minimal-ui.minimal-ui is browser.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.
When the fullscreen display mode is applied, it is RECOMMENDED that the user agent provides the end-user a means to consult common information about the web application, such as the origin, start and/or current URL, granted permissions, and associated icon. How such information is exposed to end-users is left up to implementers.
Additionally, when applying a manifest that sets the display mode to anything except "browser", it is RECOMMENDED that the user agent clearly indicate to the end-user that their are leaving the normal browsing context of a web browser. Ideally, launching or switching to a web application is performed in a manner that is consistent with launching or switching to other applications in the host platform. For example, a long and obvious animated transition, or speaking the text "Launching application X".
'display-mode' media featureThe 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.
@media all and (display-mode: fullscreen) {
...
}
#game:fullsceen{
...
}
A user agent MUST reflect the applied display mode of the web application via a CSS media query [MEDIAQ ].
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) => {
}
if (standalone.matches) {
}
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.
A resource is said to be associated with a manifest if the resource representation, an HTML document, has a manifest link relationship.
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.
This section defines algorithms for obtaining, processing, and applying 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 returned, the user agent MUST ignore the manifest declaration. In running these steps, a user agent MUST NOT delay the load event.
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.null, terminate this algorithm.href attribute's value is the empty string, then abort these steps.href attribute, relative to the element's base URL. If parsing fails, then abort these steps.manifest".crossOrigin attribute's value is 'use-credentials', then set request's credentials to 'include'.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 30 days from the time the response is sent:
HTTP/1.1 200 OK
Cache-Control: max-age=2592000
Content-Type: application/manifest+json
{
"lang": "en",
"name": "Super Racer 2000",
"start_url": "/start.html",
"display": "fullscreen",
"orientation": "landscape"
}
A user agent MUST support [CSP3 ].
The manifest-srcdefault-srcmanifest-src*, meaning that a user agent can, [FETCH ]'s 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).
manifest-srcimg-src directive controls where the icon's images can be fetched from.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 extension point is meant to help avoid issues related to monkey patching.
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 .
"{}"."{}".dir member with manifest as the argument.start_url member with manifest, manifest URL, and document URL as arguments.display member with manifest as the argument.orientation member with manifest and display mode as arguments.name member with manifest as the argument.description member with manifest as the argument.lang member with manifest as the argument.short_name member with manifest as the argument.scope member with manifest, manifest URL, document URL, start URL as arguments.related_applications member with manifest as argument.prefer_related_applications member with manifest as argument.theme_color member with manifest as argument.background_color member with manifest as argument.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.
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 [WHATWG-URL ] from which the manifest was fetched.
dir memberThe dir member specifies the base direction for the directionality-capable members of the manifest. The dir member's value can be set to one of the text-direction values.
The directionality-capable members are:
The text-direction values are the following, implying that the value of the directionality-capable members is by default:
When displaying the directionality-capable members to an end-user, the user agent MUST use the base direction to compute directional runs and layout or position text correctly in text containing mixed-direction sequences [BIDI ]. When the base direction is "auto" the user agent MUST run the steps to programmatically determine the directionality of a member - and use the resulting text-direction value to assist in displaying the value of the member.
The steps to programmatically determine the directionality of a member are as follows. The algorithm takes the value of a member.
The steps for processing the dir member is given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns one of the text-direction values.
dir".lang memberThe lang member is a language tag (string) that specifies the primary language for the values of the manifest's directionality-capable members (as knowing the language can also help with directionality).
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.
lang".undefined.false, then:
undefined.name memberThe 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.
name".undefined.short_name memberThe 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.
short_name".undefined.description memberThe description member allows the developer to describe the purpose of the web application.
The steps for processing the description member is given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a string or undefined.
description".undefined.scope memberThe 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.
scope".undefined", issue a developer warning that the type is unsupported.undefined.undefined.scope needs to be same-origin as Document of the application context.undefined.undefined.icons memberThe 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:
type member. If the user agent doesn't support WebP, it falls back to the second icon of the same size. 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.
{
"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": "257x257"
}]
}
display memberThe 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.
display" as the argument.orientation memberThe 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
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
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.
orientation".undefined.OrientationLockTypeundefined.start_url memberThe 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.
start_url".undefined", issue a developer warning that the type is unsupported.start_url needs to be same-origin as Document of the top-level browsing context.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.
start_url trackingIt's conceivable that the start_url could be crafted to indicate that the application was launched from outside the browser (e.g., "start_url": "index.html?launcher=homescreen"). This can be useful for analytics and possibly other customizations. However, it is also conceivable that developers could encode strings into the start_url that uniquely identify the user (e.g., a server assigned UUID). This is fingerprinting/privacy sensitive information that the user might not be aware of.
Given the above, it RECOMMENDED that, upon installation, or any time thereafter, a user agent allow the user to inspect and, if necessary, modify the start URL of an application.
theme_color memberThe theme_color member serves as the default theme color for an application context. What constitutes a theme color is defined in [HTML ].
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 valid [HTML ] meta element whose name attribute is "theme-color".
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.
theme_color".undefined.undefined.undefined.background_color memberThe background_color member describes the expected background color of the web application. It repeats what is already available in the application stylesheet but can be used by the user agent to draw the background color of a web application for which the manifest is known before the files are actually available, whether they are fetched from the network or retrieved from disk.
The background_color member is only meant to improve the user experience while a web application is loading and MUST NOT be used by the user agent as the background color when the web application's stylesheet is available.
The steps for processing the background_color member are given by the following algorithm. The algorithm takes a manifest as an argument. This algorithm returns a string or undefined.
background_color".undefined.undefined.undefined.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, etc.). For an image object, this specification provides developers with a means of specifying the dimensions, 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.
To fetch an image object, the user agent MUST run the steps to fetch an image object. The algorithm takes an image object, the manifest URL, and the document (Document) from which the manifest was linked. It returns a Response:
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.
sizes memberThe 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.
sizes" as the argument.undefined", issue a developer warning that the type is unsupported.undefined. sizes attribute and let keywords be the result.src memberThe 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.
src" as the argument.undefined", issue a developer warning that the type is unsupported.undefined.undefined.type memberThe 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.
type" as the argument.undefined", issue a developer warning that the type is unsupported.undefined.undefined.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.
false.src member of an image with potential image and manifest URL.undefined, move onto the next item in images (if any are left).src, type, and sizes. All properties initially set to undefined.src property to be src.type member of an image passing potential image.undefined, set image's type property to be type.sizes member of an image passing potential image.undefined, set image's sizes property to be sizes.undefined:
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 memberThe 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.
platform" as the argument.undefined.url memberThe 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.
url" as the argument.undefined.undefined.id memberThe 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.
id" as the argument.undefined.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 parser 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 [WHATWG-DOM ]:
The following are defined in [FETCH ]:
The following are defined in [HTML ]:
link elementrel attributea elementmeta elementarea elementname attributetitle elementThe following registrations are for community review and will be submitted to the IESG for review, approval, and registration with IANA.
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.
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.
A request to register the manifest link relation type been submitted to IANA.
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY , MUST , MUST NOT , OPTIONAL , RECOMMENDED , REQUIRED , and SHOULD in this document are to be interpreted as described in BCP 14 [RFC2119 ] [RFC8174 ] when, and only when, they appear in all capitals, as shown here.
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.
This section is non-normative.
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.
To allow the community can easily find extensions, please add your extensions to the Extensions Registry.
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.
This section is non-normative.
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.
We encourage implementors to add proprietary extensions to our Extensions Registry. This allows the community to track what extensions vendors and/or the web community have defined and documented. Periodically, we will consider those extensions for standardization.
The following is an example of two hypothetical vendor extensions.
{
...
"webkit_fancy_feature": "some/url/img",
"moz_awesome_thing": { ... }
...
}
link and meta elementsAn 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:
meta tags are currently using, especially when a tag's value contains several sub-values.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).
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.
It is expected that authors will localize the content of a manifest by using one of the following options:
Accept-Language" header, or even a custom HTTP header).Given the options above, developers need to be mindful of the end-user's privacy with respect to their preferred language: When the end-user has explicitly indicated their language preference to a web application (i.e., when not just using the user-agent default language settings), sending the user's preferred language in the clear over the wire is generally not OK. Doing so would reveal personal information about an end-user. As such, developers are encouraged to use [TLS ] to reduce the chances of pervasive monitoring of their Web applications [RFC7258 ].
This document attempts to address the Use Cases and Requirements for Installable Web Apps.
This document reuses text from the [HTML ] specification, edited by Ian Hickson, as permitted by the license of that specification.
Dave Raggett and Dominique Hazael-Massieux contributed to this specification via the HTML5Apps project.