FAQ

The basics

What is Nucleus Co-op?

A free, open-source Windows app that adds split-screen to PC games that don't have it. It runs one copy of a game per player, gives each copy its own controller, keyboard or mouse, connects the copies, and tiles the windows on your screen: one PC, one copy of the game, a screen for everyone.

How does it work?

Nucleus starts several copies of the same game from one installation, using linked copies of its files and closing the mutexes that would stop a second copy. Each copy answers to one player only, through Nucleus' XInput libraries, XInput Plus or Proto Input hooks. The copies connect through the game's own LAN or online mode, with emulators (Goldberg for Steam, Nemirtingas' for Epic and GOG) when the game expects a store. Nucleus keeps every window active so everyone can play at once, then removes the borders and places each window on its part of the screen.

Each game needs a handler: a small script, written by the community, that tells Nucleus how to do all that for that game.

Does it add co-op to single-player games?

No. The game needs some form of LAN or online multiplayer already, or a mod that adds one (Skyrim Together, for example). Nucleus Co-op splits the screen; the game provides the multiplayer.

Is it free?

Yes. Nucleus Co-op and every handler on the hub are free. The app is open source under the GPL-3.0, has no account, no ads and no catch, and is run by volunteers. You can support it on Patreon if you want to.

Is it safe? My antivirus flags it.

Yes. Some files Nucleus Co-op needs (the input hooks and the Goldberg emulator) look suspicious to antivirus programs because they inject into games. These detections are false positives, and the app is fully open source. Download it only from the official GitHub releases, and add its folder to your antivirus exclusions before extracting (details).

Does it work on Linux or Mac?

No. Nucleus Co-op depends on Windows features that Wine and Proton don't provide in a way it can use. It needs Windows 10 or 11 (System requirements).

Getting it running

Where do I download it?

From the download page, which links to the official GitHub releases. Take the release archive, not the "Source code" zip, and always use the latest version: new handlers are made for it.

How do I use it?

Install it, then follow Your first session. The Getting started page sums it up in five steps.

Where should I put the Nucleus Co-op folder?

At the root of a drive, for example C:\NucleusCo-op. Not in Program Files, not in OneDrive or your user folder, and never inside a game's folder. Some handlers need it on the same drive as the game, and that drive must be NTFS. Why.

Nucleus Co-op doesn't launch or crashes. How do I fix it?

Install the Visual C++ 2015-2022 runtimes (x86 and x64) and WebView2, make sure your antivirus didn't delete any of its files, extract it again with 7-Zip into a clean folder at the root of a drive, and restart your PC. The full checklist is in The app does not start.

Can I use it offline?

Yes. You only need the internet to download Nucleus Co-op, handlers, covers and screenshots. Most handlers then work fully offline; a few need the game's own servers or one account per player, and their notes say so.

Games and handlers

Which games work?

More than 600 games have a handler on the hub. Most handlers are made for the Steam version of a game. Xbox app and Game Pass versions don't work. See Supported games.

What are handlers?

Small JavaScript files that tell Nucleus Co-op how to run one game several times: which files to copy, how to restrict each controller, how to connect the copies, how to size the windows. One handler per game, written by the community. See What handlers are.

When will my game be supported?

When someone writes a handler for it. Ask on Discord or post a [Request] Name of the game on r/nucleuscoop, with the store you have it on and how its multiplayer works (LAN, online, dedicated servers). Handler authors can only work on games they own. Or write it yourself.

How do I know when a handler is updated?

The library shows Update to vN on the game, and Settings › About › Handler updates checks all your games at once. Updates are also announced in the #handlers-updates channel on Discord.

How do I create my own handler?

Start from a handler for a game on the same engine, and follow Write a handler. The Handler API reference lists every option, and handlers\MasterHandler.js in the Nucleus folder is a commented template. When it works, publish it on the hub.

Playing

Which controllers work?

Xbox 360, One and Series controllers work as they are. PlayStation, Switch and generic controllers usually need a helper that makes them look like Xbox controllers. Some handlers also support one or several keyboards and mice. See Controllers.

My PlayStation or generic controller isn't detected, or has double input

Use DS4Windows (PlayStation) or XOutput / x360ce 4 (others) to emulate an Xbox controller, then hide the real device with HidHide. Turn off Steam Input if you still get double input. Step by step.

Why isn't my keyboard or controller showing in the lobby?

Devices appear once they receive input: press a key, move a mouse, or hold a controller button for a second. If the game page says the handler supports controllers only, keyboards won't appear, and the other way round. More fixes.

How do I play with three players without an empty quarter?

Use the grow button next to a player in the lobby to stretch their window over the free place. Layouts and screens shows how.

How do I use a custom layout?

Set the rows and columns in Settings › Layout, then pick More › Custom grid under a screen in the lobby. Or use More › Manual to drop players anywhere. See Layouts and screens.

I can't move my cursor or close the game

Inputs are locked to the game windows. Press End to unlock them, or Ctrl+Q to close Nucleus Co-op and every copy. Keyboards and mice.

Where are my saves?

It depends on the handler: per player in C:\Users\<you>\NucleusCoop, or where the game normally saves. Game options in the library opens each player's save folder when the handler declares it. Saves and profiles.

Can we mix split-screen and LAN between several PCs?

Yes. Run Nucleus Co-op on each PC and connect all the copies over the LAN, for example two players split on one PC and two on another. If the handler emulates Steam, give the players on the second PC different Steam IDs in Settings › Players, or the copies will clash. Some games tie saves to the Steam ID: set player 1's to your own to keep your progress (how).

When something goes wrong

A handler doesn't launch or doesn't work

Update Nucleus Co-op and the handler, read the handler notes, run the game once on its own, close overlays, and check that the game is the Steam version on an NTFS drive. The full list.

Nucleus says it can't find a file when launching

Run the game once on its own and apply a graphics setting, so its config files exist. Then use Game options › Delete UserProfile Config Path for every player. More.

Nucleus shows a OneDrive error, or my Documents folder moved

Your Documents folder is synced by OneDrive, which conflicts with the per-player Documents folders some handlers use. Put Documents back in its default place: here's how.

The game windows look stretched

Set display scaling to 100 %, and add custom resolutions matching the player windows in your graphics driver. Performance.

The frame rate is low, or better in one window than the others

Lower the graphics settings, cap the frame rate, and press Ctrl+H to unfocus the windows so they share the PC evenly. Performance.

Where do I report a bug?

On the game's page on the hub for a handler, on GitHub for the app, or on Discord when you're not sure. Turn on the debug log first. Report a bug.

The project

How can I help?

Join the Discord, help other players, test handlers, write your own, or contribute code on GitHub. Reporting bugs well helps a lot too.

Where can I donate?

On Patreon. Nucleus Co-op is free and will stay free; supporters keep it going and get behind-the-scenes posts and early access to new versions and handlers.

Who makes it?

Nucleus Co-op was created by Lucas Assis, extended by ZeroFox, with multiple keyboards and mice and Proto Input by Ilyaki and the 2.x versions by Mikou27. r-mach makes the website, the hub and the new interface. Handlers come from the community: Talos91, PoundlandBacon, Pizzo, maxine64 and many more. The history tells the whole story.