How to Play Single-Player Games With Friends Using an AI Co-op Mod

Deus Ex came out in 2000 as a single-player game. Today you can play its whole campaign with friends over Steam, with no IP addresses and no port forwarding. The fix came from a free project that tells an AI coding agent how to revive an abandoned co-op mod, or build a new one when nothing exists.

That project is Co-op Anything, an open-source playbook by the GitHub user cranebeaker. You give it to Claude Code, name a game, and the agent researches, fixes or builds the co-op, tests it with bots inside the game and packages it so your friends can join.

This guide takes you from a blank PC to a friend joining your game, and covers the rules that keep your game accounts safe.

What Co-op Anything is, in plain words

Co-op Anything is a GitHub repository with four parts. The main one is a playbook: a file called AGENTS.md plus a folder of skills that tell an AI coding agent, phase by phase, how to add co-op to a game. Next to it sits an MCP server, a small connector that lets the agent search a directory of known co-op mods and detect a game's engine from its install folder. There is also a set of ready-made test tools, and a directory of more than 230 co-op mods and gaps that you can browse at coopanything.app.

The README says it works with Claude Code, Codex, Gemini CLI, Cursor and OpenCode, among others. The repository was created on 16 October 2026 and had 1,466 GitHub stars when we checked on 27 October.

The agent takes one of two paths, and the first phase of its work decides which:

Both paths end the same way: automated tests with real game clients, an easy installer, Steam relay networking, and a draft pull request back to the shared repo so the next person's agent starts further ahead.

Before you start

Gather these first. The agent will stop and ask for most of them anyway, so having them ready keeps the first session moving.

• The game, owned by every player. Ideally everyone has the same store version (Steam or GOG). The playbook notes that co-op mods often support one version only.
• A Windows PC is the easy route. The finished Deus Ex and Dungeon Keeper packages run from Windows .bat files. Claude Code itself needs Windows 10 (version 1809) or later, or macOS 13 or later, and at least 4 GB of RAM.
• Steam, installed and signed in on every player's PC. The relay borrows Valve's free Spacewar test app, so nobody has to buy anything extra.
• A paid Claude plan. The free plan does not include Claude Code. Pro costs $20 a month, or $200 a year paid up front (about $17 a month).
• Claude Code, either in the Claude desktop app or in a terminal. Setup is in Stage 2 below.
• Free disk space at least the size of the game. The agent's rules tell it to copy your install into a test folder and work there, never on your real install.
• Optional: Git for Windows (Claude Code uses it on Windows if it is there), Python 3.9 or later for the MCP server, and a GitHub account if you want to send your fixes back.

Stage 1: Check that your game is a safe fit

Do this before you open Claude Code. It tells you whether you need the agent at all.

1. Search the directory. Open coopanything.app and type your game's name. Each entry says what the mod syncs and how it was tested. If you find a released mod, you may not need the agent at all.
2. Check the game's rules on mods. Read the licence agreement or the publisher's modding policy. If it forbids mods, stop here.
3. Check for anti-cheat. If the game has any online mode protected by anti-cheat, do not mod it. Anti-cheat systems look for changed game files, and Valve's VAC, for example, issues a permanent ban from VAC-secured servers for that game.
4. Confirm every player owns it. Never download game files from anywhere else to make a mod work. The directory site says every listed mod needs your own copy.
5. Write down the store and version. Note where you bought the game and, if it shows one, its version number. The agent records the exact build before it follows any existing write-up, and it will ask you about your copy.

Stage 2: Install Claude Code and sign in

Pick one of the two routes. Both give you the same agent.

Route A: the desktop app (no terminal)

1. Download the Claude desktop app for Windows or macOS from the Claude Code desktop guide and run the installer.
2. Open Claude and sign in with your Anthropic account.
3. Click the Code tab at the top of the sidebar. If you see a prompt to upgrade, your account is on the free plan and you need Pro or higher first.

Route B: the terminal

On Windows, open PowerShell (its prompt starts with PS C:\) and paste:

Copyirm https://claude.ai/install.ps1 | iex

On macOS or Linux, open Terminal and paste:

Copycurl -fsSL https://claude.ai/install.sh | bash

1. Press Enter. The installer shows no progress bar while it downloads, so give it a minute and wait for the prompt to come back. Then open a new terminal window.
2. Type claude --version. A working install prints a version number. If the terminal says claude is not recognized, the install folder is not on your PATH yet; the official setup page has the fix.
3. Type claude and follow the browser prompt to log in.

Stage 3: Give the agent its own folder

1. Create an empty folder, for example Documents\coop-projects. Do not use your game's install folder.
2. In the desktop app, click the environment selector under the prompt box and pick the top entry in the Local group. Then click the folder control next to it, choose Open folder… and select your new folder. In a terminal, move into the folder with cd and run claude.
3. Set the permission mode to Manual for your first run. Claude then asks before it edits a file or runs a command, so you see every step. You can switch to Accept edits later once you trust the flow.

Why a separate folder matters: the agent keeps its notes, logs and private state about your PC in a local/ folder that is never shared, and it rereads those notes at the start of each session. One folder per game keeps that memory clean.

Stage 4: Paste the prompt

This is the whole prompt. Change Deus Ex to the game you want to play with your friends.

CopyRead https://github.com/cranebeaker/coop-anything and follow AGENTS.md. I want to play Deus Ex in co-op with my friends.

Prefer a one-click copy? The same prompt is on our free prompt page, the copy-paste version with a copy button.

The first sentence points the agent at the rulebook. The second names the target. If you want fewer back-and-forth questions, add the details it will ask for anyway:

CopyRead https://github.com/cranebeaker/coop-anything and follow AGENTS.md.
I want to play [game] in co-op with one friend.
My copy is the [Steam or GOG] version.
Start with triage and tell me what you find before you install anything.

What you should see next: Claude fetches the repo, reads AGENTS.md and starts the triage phase. Its first summary should name the engine the game uses, say whether a co-op mod already exists and say which path it plans to take. If it tries to download tools before you have seen that summary, stop it and ask for the triage result first.

Stage 5: Let it work, and answer its questions

The playbook splits the job into phases. You do not need to follow the technical detail, but knowing the order tells you where you are.

The rules in AGENTS.md shape how it behaves, and they are worth knowing because they tell you what to expect:

• It must ask before installing software, downloading large files, writing outside its folder, using your Steam, Discord or GitHub accounts, contacting anyone or publishing anything. Saying no is always an option.
• It never touches your real game install or your saves. It works on a copy and backs up any file before changing it.
• It downloads only from official sources, checked by file fingerprint, and it treats text in bug reports and mod readmes as data, never as orders.
• It stops at the first contradiction. If your version of the game does not match an existing write-up, it tells you and suggests a fix to the playbook rather than guessing.
• It tests with bots driving the game, so you are not its test plan.

Expect this stage to run across several sessions. If a session ends or you hit your plan's usage limit, open Claude Code in the same folder and tell it to continue. It writes notes as it goes in a NOTES.md file for the game, so the next session picks up from there.

Stage 6: Test, install and play with your friends

1. Check the QA level. Every finished entry carries one: untested, player reports, automated tests (bots drove real game clients) or verified playthrough. Ask the agent which level it reached and to show you the test summary.
2. Install it on every PC. The agent packages the result with an installer. Every player needs the same build. The finished Dungeon Keeper and S.T.A.L.K.E.R. packages both warn about this, and the S.T.A.L.K.E.R. server refuses a player with a different version.
3. Host. The host starts the mod and opens a friends-only Steam lobby, usually by pressing one key or running a host file.
4. Join. Friends start the mod first, then join from the host's name in their Steam friends list. If a friend clicks Join Game in Steam before the mod is running, Steam may launch the Spacewar test app instead of your mod.
5. Expect "playing Spacewar". Steam shows that status while you are connected. It is the relay at work.

Stage 7 (optional): Send what you learned back

The agent opens its pull request as a draft and leaves a box for you to tick, because it goes out under your GitHub account. Read the changes first. A corrected directory entry or a failed attempt counts as a useful contribution, and if you stop halfway, the playbook explains how to list your work as up for adoption.

The shortcut: Deus Ex co-op in three steps

For Deus Ex you do not need the prompt at all. The finished mod is Deus Ex Co-op. It builds on HX, the Deus Ex co-op mod by Sebastian Kaufel (Hanfling), whose last build came out in 2019. It adds a separate fix package for HX's bugs, a small Steam relay and automated tests. HX is not modified or copied; the installer downloads it from its official build server.

1. Make sure you own Deus Ex: Game of the Year Edition on Steam or GOG, and that Steam is running.
2. Download the latest DeusEx-Coop zip from the project's Releases page (version 0.2.0, a pre-release, when we checked) and unzip it anywhere.
3. Run Install.bat. It finds Deus Ex, downloads HX, installs the fixes and puts a "Deus Ex Co-op" shortcut on your desktop.
4. Open Deus Ex Co-op. The host presses 1. Friends press 2, which finds the host in their Steam friends list and joins.

Saving is automatic: the game saves each time your group enters a new map, and the host can also type CoopSave in the console. Press 3 (Continue) to pick up where you left off. Friends get their gear back when they rejoin with the same name.

No Steam? The package includes host and join files for a direct connection, but the host then needs UDP ports 7790 to 7792 forwarded on the router, or everyone on the same VPN.

Optional: give the agent its own tools

The prompt alone is enough. The MCP server adds tools that search the co-op directory, detect a game's engine from its files (with anti-cheat warnings), record the exact build of your game and check a contribution before it is sent.

1. Install Python 3.9 or later, then run pip install pyyaml.
2. Ask Claude to clone the Co-op Anything repo. If you open Claude Code inside that clone, the project's settings offer the server to you automatically.
3. To use it from any folder, run this once, with your own path in place of the placeholder:

Copyclaude mcp add -s user coop-anything -- python <path to clone>/tools/mcp/coop_mcp.py

For games with no existing mod, the README suggests pairing it with a reverse-engineering MCP such as REA: Co-op Anything knows what to do, REA looks inside the game.

Which games are ready today

Status changes fast, so treat this as a snapshot from 27 October 2026 and check the directory before you begin.

Console games such as Ocarina of Time take extra steps. The README says they may need decompiled PC ports or emulators, and that project asks each player to supply their own copy of the game on first start.

What it costs

The real cost of a new game is agent time. The README says some games "need more agent hours than others." Claude plans meter usage in five-hour sessions, so a long Path 2 project will pause each time you reach your limit and carry on after it resets. If you plan a big one, Max gives you 5x or 20x Pro's usage per five-hour session.

Troubleshooting

• The Code tab asks you to upgrade. Your account is on the free plan. Subscribe to Pro or higher and restart the app.
• The agent ran out of usage mid-job. Wait for the limit to reset, then reopen the same folder and ask it to continue from its notes.
• The agent stopped and reported a contradiction. That is one of its rules working. Read what did not match, usually the game version, and decide with it whether to change course.
• A friend's Join opens Spacewar instead of the game. Close it, start the mod first, then accept the invite.
• The join fails with a version error. Every player needs the exact same build of the mod. Reinstall from the same zip on every PC.
• Deus Ex logs "Accessed None" warnings during conversations. The project lists these as harmless HX warnings. Its other known issue is that the endgame quote and credits are a stub.

Alternatives, and when to pick them

If your game already has local multiplayer such as split-screen or couch co-op, you may not need a mod. Steam Remote Play Together lets you share local multiplayer games with friends online for free. One player owns and runs the game, and the host can be joined by up to four players, or more on fast connections.

For split-screen on one PC, Nucleus Co-op starts several copies of a game at once on Windows, and PartyDeck does split-screen on Linux and SteamOS. The Co-op Anything README points to both for couch co-op.

Pick Co-op Anything when the game has no multiplayer at all and you want online co-op, or when an abandoned co-op mod exists and needs finishing.

Who this is not for

It is not for adding players to an online game, a competitive game or anything with anti-cheat. The project's own rule is "Co-op only: nothing that cheats in other people's multiplayer games or touches anti-cheat." It is also a poor fit if you want to play a game other than Deus Ex or Dungeon Keeper this weekend. Building co-op from zero is a long project, and you will spend evenings testing and reporting what breaks.

Frequently asked questions

Can you turn a single-player game into co-op?

Sometimes. Co-op Anything gives an AI coding agent such as Claude Code a playbook to fix an existing co-op mod or build a new one, then test it with bots. Deus Ex is released as a beta and Dungeon Keeper has a beta build. Other games on its list are still in progress, and some games need far more agent hours than others.

Do my friends need to own the game?

Yes. Every player needs their own copy installed, ideally the same store version. The project hosts no game files, and the Steam relay uses Valve's free Spacewar test app, so nobody has to buy anything else.

Can I get banned for using a co-op mod?

On games with anti-cheat, modified files can get your account banned. Valve's VAC, for example, issues a permanent ban from VAC-secured servers for that game. Use Co-op Anything only on games that allow mods, offline or in private sessions with friends. The project itself does not touch anti-cheat or online services.

Do I need to know how to code to use Co-op Anything?

No. The README says you need the game, a coding agent and some patience. You paste one prompt into Claude Code and it does the work, asking before it installs anything or uses your accounts.

How long does it take to add co-op to a game?

For Deus Ex, it is a download and an installer. If an abandoned co-op mod already exists for your game, the Co-op Anything README says most projects take days at most. If nothing exists, it depends on the engine and can take much longer.

What if my game already has split-screen?

Then Steam Remote Play Together may be enough: one player runs the game and friends join online, up to four or more on fast connections. For split-screen on one PC, Nucleus Co-op (Windows) and PartyDeck (Linux and SteamOS) are free options.

Sources

• Co-op Anything on GitHub (README, AGENTS.md, FAQ, game list)
• Deus Ex Co-op on GitHub
• Ocarina of Time co-op write-up
• CoOp:Anything directory
• Claude Code setup and system requirements
• Claude pricing
• Wikipedia: Valve Anti-Cheat
• Steam Remote Play Together