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This guide takes you from a fresh machine to a completed Steam build upload. It assumes you already have a Steamworks partner account and your game’s app and depot IDs. The whole process takes about five minutes once your ContentBuilder directory is in place.
1

Download Onyx

Go to the Onyx GitHub Releases page and download the latest release for your platform:
  • Windows — OnyxUploader.exe
  • Linux — OnyxUploader.x86_64
Onyx is a single self-contained executable. No installer or additional runtime is required. Place it anywhere on your machine.
On Linux, you may need to mark the file as executable before it will run. See the installation guide for details.
2

Confirm your Steamworks ContentBuilder is ready

Onyx requires the Steamworks SDK’s ContentBuilder tool to already be installed. If you have not set it up yet, download the Steamworks SDK from the Steamworks partner site and locate the tools/ContentBuilder/ directory.Your ContentBuilder directory must contain these three subdirectories before Onyx will accept it:
ContentBuilder/
├── builder/          # Windows SteamCMD (steamcmd.exe)
├── builder_linux/    # Linux SteamCMD (steamcmd.sh)
├── content/          # Your game files go here
├── output/           # SteamCMD writes logs here
└── scripts/          # VDF build configs go here
The content/, output/, and scripts/ subdirectories are required. Onyx validates for these when you set the ContentBuilder path and will show an error if any are missing.
3

Launch Onyx and point to ContentBuilder

Run OnyxUploader.exe (Windows) or OnyxUploader.x86_64 (Linux).On first launch, Onyx opens a setup dialog. Click Browse and select your ContentBuilder directory. Onyx checks for the required subdirectories and saves the path to settings.cfg next to the executable so you do not need to set it again.
4

Add your Steam account

Click Manage Users to open the Users panel. Enter your Steam username and password, then click Add User. You can add multiple accounts and switch between them at upload time.
If you toggle Save before clicking Add User, credentials are saved to settings.cfg in plain text next to the executable. Do not place Onyx in a shared or publicly accessible directory if you store credentials.
5

Select an app and start the upload

In the Apps panel, select the app you want to upload. Onyx reads the corresponding app_<APPID>.vdf file from the scripts/ directory. If no VDF exists yet, open the Setup dialog to create one from the built-in template.Select a user account in the Users panel, then click Upload. Onyx calls SteamCMD with your credentials and the VDF path, and streams the output to the console panel in real time.
6

Handle Steam Guard if prompted

If the selected account has Steam Guard enabled, SteamCMD will pause and wait for a verification code. Onyx detects this after 5 seconds of idle output and shows a yellow warning in the console panel. Switch to the SteamCMD window (check your taskbar), enter the code from your email or mobile authenticator app, and press Enter. The upload resumes automatically.
To avoid Steam Guard prompts on every upload, log in interactively once using SteamCMD directly to cache the session. Subsequent uploads from Onyx on the same machine will not require a code until the cached session expires.

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What happens next

When the upload completes, SteamCMD writes a log to the output/ directory inside your ContentBuilder folder. You can review it there or in Onyx’s console panel. Check the Steamworks partner dashboard to confirm the build has been received and set the branch live.

Installation

Full prerequisites and platform-specific setup details.

Managing apps and depots

Add, edit, and organize your app and depot VDF configs.

Managing users

Set up and switch between multiple Steam accounts.

Steam Guard reference

How Onyx detects and handles Steam Guard during uploads.

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