The goal of these requirements is to ensure that the applications hosted on Flathub are safe to use and integrate well in the desktop experience.

If you have any further questions, please ask on #flatpak on ircs:https://chat.freenode.net

All content hosted on Flathub must allow legal redistribution, and the license must be correctly specified in the app's appdata file. Non-redistributable files can be downloaded at install time using the extra-data source type.

Each application should have a unique application ID, following the standard reverse-DNS schema. See the Flatpak documentation for more information on this.

The manifest must be at the top level and named after the application ID with the extension .json. All patches and data files required also go in the repository.

Flathub only hosts stable application releases, and not development snapshots. Manifests should therefore refer to tarballs or git tags and not the tip of a branch.

When building from a git tag, both the tag name and the commit id should be specified, like so:

   "tag": "1.0.4",
   "commit": "cdfb19b90587bc0c44404fae30c139f9ec1cca5c"

This ensures that the build is reproducible, since tag can change their values over time. A commit can also be specified without a tag, however tag names are encouraged as they better for readability.

Flathub always builds in the flatpak branchname "stable" and it always passes --default-branch=stable. This means that a branch key doesn't need to be specified. If one is specified, it should be "stable".

Applications must be built against an SDK that is itself hosted on Flathub. This requirement also applies to SDK extensions that may be required in order to build an application. The easiest way to see which runtimes are currently available is to install the flathub remote and run:

flatpak remote-ls --runtime --show-details flathub

Bundled dependencies should meet the requirements on this page, including the license requirements.

Take care to check the build directory for unnecessary files. These should be added to cleanup, in order to ensure smaller package sizes.

A small number of dependencies that are frequently used by applications have been collected in the shared-modules repository, for use by applications being distributed with flathub. These can be used as a git submodule, like so:

git submodule add https://github.com/flathub/shared-modules.git

These can be specified from manifest .json files, like:

"modules": [
  "shared-modules/SDL/SDL-1.2.15.json",
  {
    "name": "foo"
  }
]

It is fine to patch dependencies, but please send these upstream wherever possible!

Flathub is primarily focused on graphical desktop applications and not CLI/TUI applications. The following requirements ensure effective desktop integration.

Appstream is the standard used to provide metadata about applications. Applications must provide appstream data and:

• pass appstream-util validate-relax (bonus points for validate or validate-strict).

• include a description.

• include releases with versions and include changelogs.

• include OARS information, especially for games.

• if application metadata has not been provided by the upstream, license it with Creative Commons Zero, version 1, by stating CC0-1.0 in metadata_license.

For information about appstream, see its documentation.

Applications must include a desktop file and pass desktop-file-validate.

See the desktop file spec for more details.

Applications must provide application icons at 64×64px and 128×128px sizes. Application icons should either be included as scalable SVGs or high-resolution PNGs.

The Flatpak sandbox is still a work in progress. However, permissions should still be limited as much as possible (see man flatpak-metadata for an overview of permissions).

The following permissions can be freely used:

• --share=network
• --share=ipc
• --socket=x11
• --socket=wayland
• --socket=pulseaudio
• --device=dri

Applications should not grant --socket=system-bus or --socket=session-bus, unless they are development tools. The --log-session-bus and --log-system-bus flags can be used with flatpak run in order to track down usage.

By default you are granted access to --own-name=$your_app_id any ownership beyond that is usually questionable but there are exceptions such as org.mpris.MediaPlayer2.$media_player_name.

Talk permissions are largely unrestricted but always try to use the minimum subset needed.

Applications should ideally use portals for file access. Further file access is often necessary and is acceptable, although it should be limited as much as possible.

Additional recommendations:

• For access to XDG directories, variables such as xdg-music and xdg-run/foo are recommended (see man flatpak-metadata).

• Always append :ro if write access is not needed.

• If an application hardcodes a path in $HOME and you don’t grant home access you can use --persist and it will map the $HOME directory to your private directory e.g. --persist=.mozilla. If the application takes args to set config/data dirs then use them.

• Do not attempt to retain configs from non-flatpak installations. While possible it is recommended that flatpak installs stay self-contained.

• If an application uses $TMPDIR to contain lock files or shared files with other process create a wrapper script that sets it to $XDG_CACHE_HOME.

While not ideal, --device=all can be used to access devices like controllers or webcams.