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Launch Options Guide

Unifideck lets you customize how your games launch by adding extra options to the Steam shortcut. This covers things like performance overlays, frame generation, trainers, debug tools, and game-specific tweaks — all without needing to modify any config files by hand.

Where to Set It

  1. Open your Steam Library
  2. Right-click the game → Properties
  3. Under Shortcut → Launch Options

You'll normally see just the game's identifier here, e.g.:

epic:Salt

or, if Proton (Force Compatibility) is enabled:

/home/deck/homebrew/plugins/Unifideck/bin/unifideck-launcher "epic:Salt" #%command%

Don't touch the store:game_id part or the launcher path — Unifideck needs those to identify and launch the game. Everything you add goes after the game ID.

What You Can Add

1 — Environment Variables

These are NAME=value settings that get passed to the game at launch. You can add any number of them after the game ID.

gog:1103900211 MANGOHUD=1 DXVK_HUD=fps

Unifideck automatically recognises any ALL_CAPS_NAME=value style entry (letters, numbers, and underscores in the name) and exports it for the game. You don't need to stick to a predefined list — common examples:

What you type What it does
MANGOHUD=1 Turns on the MangoHud overlay
mangohud=1 Same — lowercase is fine too
DXVK_HUD=fps,frametime Shows DXVK frame stats
PROTON_ENABLE_NVAPI=1 Enables Nvidia API emulation
PROTON_REMOTE_DEBUG_CMD="/path/to/trainer.exe" Runs a trainer alongside the game
PRESSURE_VESSEL_FILESYSTEMS_RW=/home/deck/Games/Trainers Grants the game access to a folder
STEAM_COMPAT_MOUNTS=/mnt/games Mounts extra storage inside the game container
~/lsfg or LSFG=1 Enables LSFG frame generation — see Frame Generation (LSFG) below
PROTON=GE-Proton10-10 Forces a specific Proton version

Note

Values with spaces must be quoted, e.g. PROTON_REMOTE_DEBUG_CMD="/home/deck/Games/Trainers/My Trainer.exe"

2 — Wrapper Programs

A wrapper runs before the game, wrapping around it. Put the wrapper path before the game ID:

gog:1103900211 /usr/bin/gamemoderun

Or with tilde shorthand:

epic:Salt ~/fgmod/fgmod

The game still launches normally — the wrapper just gets to intercept or modify the process.

Combining Options

You can freely mix all three types in a single launch options field. Order doesn't matter for environment variables:

gog:1103900211 MANGOHUD=1 PRESSURE_VESSEL_FILESYSTEMS_RW=/home/deck/Games/Trainers PROTON_REMOTE_DEBUG_CMD="/home/deck/Games/Trainers/My Trainer.exe"

Or with a wrapper and game argument:

epic:Salt ~/fgmod/fgmod MANGOHUD=1

Unifideck sorts everything out:

  • store:game_id → identifies the game
  • ALL_CAPS=value entries → exported as environment variables
  • Paths or commands before the game ID → run as wrappers around the game

Caution

Do not add %command% to your launch options. Unlike native Steam games, Unifideck doesn't use Steam's process substitution — the launcher handles everything internally. Adding %command% will cause it to be passed as a literal argument and the game will not start correctly.

How Proton / Force Compatibility Interacts

When you enable Force Compatibility (Proton) through Steam's Properties:

  • Unifideck saves your Proton version choice to its own config
  • It temporarily rewrites the launch options to a bypass format (so Steam doesn't try to run the launcher itself through Wine)
  • When you open the game page, it restores the simple format
  • Your custom parameters are always preserved through this process

You can change Proton version at any time without losing anything you've added to Launch Options.

Frame Generation (LSFG)

Unifideck supports LSFG frame generation through the lsfg-vk Vulkan layer. It works the same way as on native Steam games — add ~/lsfg to your launch options:

epic:Salt ~/lsfg

You can also use LSFG=1:

epic:Salt LSFG=1

Both forms do the same thing: Unifideck reads the ~/lsfg script (generated by the LSFG-VK plugin) and exports its environment variables so the Vulkan layer picks up the right profile. You can combine it with other options:

gog:1103900211 ~/lsfg MANGOHUD=1

~/lsfg %command% (the Steam-standard syntax) also works — %command% is simply ignored.

Requirements

  1. Lossless Scaling purchased on Steam — provides the frame generation DLL
  2. Decky LSFG-VK plugin installed via Decky Loader — provides the Vulkan layer and configuration UI
  3. A profile configured in the LSFG-VK plugin settings

The Lossless Scaling app does not need to be running — lsfg-vk loads the DLL directly from disk.

Note

LSFG only activates when you explicitly add ~/lsfg or LSFG=1 to a game's launch options. Having the LSFG-VK plugin installed does not affect games without these options.

Troubleshooting

Parameters seem to disappear — Make sure you're on the latest plugin version. Custom parameters are preserved across syncs, installs, and Proton toggles.

A variable isn't being picked up — Check that the name is in ALL_CAPS_WITH_UNDERSCORES format with no spaces around the =. Values with spaces must be quoted: VAR="value with spaces".

Wrapper isn't running — Make sure the path is correct and the file is executable. Tilde paths (~/my/script.sh) work fine.

Game doesn't start at all — Don't remove the store:game_id from the launch options, and don't modify the launcher path or #%command% when Proton is active. Unifideck manages those automatically.