Webxdc Specification

Webxdc is a fresh and still evolving way of running web apps in chat messengers. This document is for app developers and outlines the webxdc API and .xdc file format. It also describes the constraints for a messenger implementation when running webxdc apps.

Webxdc API

Webxdc apps are shared in a chat and each device runs its own instance on the recipients device when they click "Start". The apps are network-isolated but can share state via sendUpdate() and setUpdateListener().

Messenger implementations expose the API through a webxdc.js module. To activate the webxdc API you need to use a script reference for webxdc.js in your HTML5 app:

<script src="webxdc.js"></script>

webxdc.js must not be added to your .xdc file as they are provided by the messenger. To simulate webxdc in a browser, use the webxdc.js file from Hello.

Webxdc File Format

  • a Webxdc app is a ZIP-file with the extension .xdc
  • the ZIP-file MUST use the default compression methods as of RFC 1950, this is "Deflate" or "Store"
  • the ZIP-file MUST contain at least the file index.html
  • the ZIP-file MAY contain a manifest.toml and icon.png or icon.jpg files
  • if the webxdc app is started, index.html MUST be opened in a restricted webview that only allows accessing resources from the ZIP-file.

The manifest.toml File

If the ZIP-file contains a manifest.toml in its root directory, the following basic information MUST be read from it:

name = "My App Name"
source_code_url = "https://example.org/orga/repo"
  • name - The name of the webxdc app. If no name is set or if there is no manifest, the filename is used as the webxdc name.

  • source_code_url - Optional URL where the source code of the webxdc and maybe other information can be found. Messenger implementors may make the url accessible via a "Help" menu in the webxdc window.

Icon Files

If the ZIP-root contains an icon.png or icon.jpg, these files are used as the icon for the webxdc. The icon should be a square at reasonable width/height, usually between 128 x 128 and 512 x 512 pixel. Round corners, circle cut out etc. will be added by the implementations as needed; do not add borders or shapes to the icon therefore. If no icon is set, a default icon will be used.

Messenger Implementation

Webview Constraints for Running Apps

When starting a web view for a webxdc app to run, messenger implementors:

  • MUST deny all forms of internet access. If you don't do this unsuspecting users may leak data of their private interactions to outside third parties. You do not need to offer "privacy" or "cookie" consent screens as there is no way a WebXDC app can implicitly transfer user data to the internet.

  • MUST allow unrestricted use of DOM storage (local storage, indexed db and co), but make sure it is scoped to each webxdc app so they can not delete or modify the data of other webxdc content.

  • MUST inject webxdc.js and implement the Webxdc API so that messages are relayed and shown in chats.

  • MUST make sure the standard JavaScript API works as described at Other APIs and Tags Usage Hints.

UI Interactions in Chats

  • Text from update.info SHOULD be shown in the chats and tapping them should jump to their webxdc message

  • The most recent text from update.document and update.summary SHOULD be shown inside the webxdc message, together with name and icon.
    Only one line of text SHOULD be shown and truncation is fine as webxdc devs SHOULD NOT be encouraged to send long texts here.

  • A "Start" button SHOULD run the webxdc app.

Example Messenger Implementations