Developer SDK

Put it on your release

1. Publish a release on GitHub under your own repository, with the version in the tag, such as v1.2.0, and one file with the mod, such as LabCoop-1.2.0.zip.
2. Attach multiplayereverything.json to the same release as its own file, next to your zip, not inside it.
3. Add your mod on the developer hub. When we approve it, we read the file, pin that release and its checksums, and offer the mod in the launcher.

A new version is a new review. Nothing reaches players on its own.

Attach it automatically

Keep the file in your repository. This workflow adds it to every release you publish.

name: Attach the launcher file
on:
  release:
    types: [published]
permissions:
  contents: write
jobs:
  attach:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - run: gh release upload "${{ github.event.release.tag_name }}" multiplayereverything.json --clobber
        env:
          GH_TOKEN: ${{ github.token }}

A Flash game

For a Flash game the file says what the game is, and the launcher does the rest. It downloads your game file from the release and checks it. It makes the same buttons every Flash game in the launcher has: Play online, rooms for up to your player count, host and join by IP, and an offline button. Then it starts Ruffle Together with your game file and key map. You never write a command line.

{
  "format": 1,
  "repo": "someone/lab-flash",
  "flash": {
    "game": "Lab Flash",
    "file": "LabFlash_coop.swf",
    "keys": "lab-flash.keys",
    "maxPlayers": 3,
    "offline": { "local": true },
    "ruffle": "1.0.3.7"
  }
}

• file and keys are files of the same release, by name. keys can also name a key map Ruffle Together has built in, such as gun-mayhem-2.
• maxPlayers is how many play online, 2 to 6.
• offline adds the offline button: {} for one player on their own, "local": true for everyone on one keyboard. It's optional.
• ruffle is the oldest Ruffle Together your game works in. Players on an older one are asked to update first.
• It needs Multiplayer Everything 1.0.43 or newer. Older launchers show your game and ask players to update.

What we check

• Only the keys the launcher knows. Anything else, anywhere in the file, is refused.
• Your mod only writes inside the game's folder, and starts only through Steam.
• You never write the download address or the checksum. We take them from the release we approved.
• No game files in your release. Only your mod.