Co-op Anything

Any single-player game. Your friends. Your agent does the work.

Quick start · How it works · What you can co-op · Games so far · Contribute · FAQ · Docs

Want to play a single-player game with your friends? Point your AI coding agent at this repo. It researches what exists, reverse engineers the game and its engine if it has to, builds or fixes the co-op, tests it with bots inside the game, and packages it so your friends install it in one click and join over Steam without port forwarding.

The sky is the limit. Every game that runs on your PC is a candidate.

Playing on one PC? Couchlink runs a copy of the game for each player, each with their own part of the screen, their own controller or keyboard and mouse, and their own Steam account if they want one. It works with co-op mods and with games that only play online. Mods made here can plug into it: see the couchlink skill.

Games being made co-op right now: Deus Ex (released) · Fallout: New Vegas · Zelda: Ocarina of Time (fully synced) · Dungeon Keeper · S.T.A.L.K.E.R. Shadow of Chernobyl

From the community: Mega Man X and Mega Man X4 (native PC with co-op netplay) · Pilotwings 64 (split-screen) · Crab Champions · Stacklands · Half Sword · Enter the Gungeon · Clive Barker's Jericho · Poppy Playtime · Divinity II (split-screen) · Command & Conquer 3 (campaign co-op) · Far Cry 2 · Gothic 3 · Fear & Hunger · Modern Warfare 2 (campaign co-op) · Little Nightmares (on our Discord) · yours next?

Quick start

Tell your agent (Claude Code, Codex, Gemini CLI, Cursor, OpenCode, ...):

Read https://github.com/cranebeaker/coop-anything and follow AGENTS.md.
I want to play <game> in co-op with my friends.

The agent follows AGENTS.md and the skills in .agents/skills (also in .claude/skills for Claude Code).

Add the MCP server

The Co-op Anything MCP lets any agent search the co-op directory, detect a game's engine from its install folder, read the playbook and skills, and validate contributions. Claude Code picks it up from this repo's .mcp.json; for other agents:

claude mcp add coop-anything -- python <clone>/tools/mcp/coop_mcp.py

Codex, Gemini CLI and Cursor setup: playbook/mcp.md. For the binary work, pair it with a reverse-engineering MCP such as REA (npx rea-agents setup): Co-op Anything knows what to do, REA looks inside the game.

How it works

Your agent takes one of two paths.

	Path 1: finish what exists	Path 2: build it from zero
When	A co-op mod exists but is buggy, stalled or abandoned. Most loved games are here.	Nothing usable exists.
How	Find the last build, mine its bug reports (issues, forums, Discord), audit the code, fix it as a separate package, test, ship.	Reverse engineer the game and engine, hook in, show the second player, sync enemies, world and story, handle level changes and saves, test, ship.
Skills	coop-research, coop-revive, coop-qa, couchlink	coop-reverse-engineer, coop-build-from-zero, coop-networking, coop-sync-testing, coop-qa, couchlink
Guide	Reviving abandoned mods	How co-op mods work

Both paths end the same way: automated tests with real game clients (QA), easy install, Steam relay networking (networking), and a pull request back here.

Sync test tools

Ready-made, game-agnostic tools for building and testing co-op sync, in tools/. Each has tests, mutation twins and one command that prints ALL OK (python -I tools/test_all.py runs them all).

Tool	What it does
chaos	UDP relay that adds lag, loss, reorder, duplicates and one-way cuts between real clients, with live control
flight	Flight recorder for your mod plus an analyzer: lines up 2 to 4 machines, finds the first desync, shrinks it and writes a regression test
fuzz	Seeded N-player co-op fuzzer with invariant oracles (converge, no double apply, one owner, no dupes, nothing stale)
ownership	Small C++ library: one owner per NPC with epochs, handoff, and stale echo rejection
fakeworld	Example in-memory game world for testing sync without launching the game
gameslot, gamepool	Lock and warm pool for running several game copies on one PC safely
scenarios, bots	JSON start states plus multi-bot co-op playbooks with a state diff after each step
animcheck	Compares animation and pose across machines and flags sliding, T-poses, floating and rubber-banding
bridge, inspect	An RPC server template for inside your game (console line, state dump, save, load, screenshot) with a Python client, plus a live side-by-side view of every copy
hotreload	Split your mod into a loader and a core, and swap the core inside the running games instead of restarting them
mutants, buildlock	Runtime mutation twins for every fix, and a shared build lock with a build cache

Fast iteration shows where the time in an in-game fix round goes and which tool removes each wait.

They come from the fnv-coop project. The coop-sync-testing skill tells your agent when to use which.

What you can co-op

Your game is...	Typical approach	Tools your agent uses
On an engine with multiplayer already (Unreal 1/2, Source, id Tech, X-Ray)	Make the single-player logic run on the existing netcode with script mods	Script source, SDK compilers, mod packages
Bethesda (Gamebryo, Creation)	Script extender plugin, host-authority sync, reuse Tilted Online style designs	SKSE / F4SE / xNVSE, Ghidra, REA
Unity	Harmony patches through a mod loader, a networking library in C#	BepInEx, MelonLoader, dnSpyEx, Il2CppDumper
Unreal Engine 4/5	Lua or C++ mods with an SDK dump of the game's classes	UE4SS, Dumper-7
RE Engine, FromSoftware, other proprietary	DLL hooks; extend the game's own online features where they exist	REFramework, MinHook, Ghidra, REA, x64dbg
Decompiled or open source (N64 decomps, KeeperFX, OpenMW, source ports)	Add networking directly in the code	A compiler, the decomp, Docker cross builds
Console only (PS1, PS2, N64, Dreamcast, GameCube, Wii, GBA, ...)	Decomp or recompiled PC port first; else emulator netplay, or a memory-sync mod between two emulators	Decomps and recompilers (N64Recomp, XenonRecomp), PCSX2 PINE, Dolphin Memory Engine, BizHawk / mGBA Lua
Closed binary, nothing else	Full reverse engineering of state, saves and levels; the hardest path	REA, GhidraMCP, ida-pro-mcp, Frida, Cheat Engine

Console games: emulator co-op and decompiled or recompiled PC ports, the route Ocarina of Time co-op took.

Couch co-op on one PC? Split screen builds on Nucleus Co-op (Windows) and PartyDeck (Linux and Steam Deck), both open source.

Full tool list with install notes: playbook/tools.md. Which engine has co-op work you can reuse: playbook/engine-families.md.

Games so far

Game	What was done	Release	Write-up
Deus Ex (2000)	Revived the HX co-op mod: fix package, Steam relay, automated test suite	deus-ex-coop	games/deus-ex
Dungeon Keeper (1997)	Shared-keeper co-op on KeeperFX, Steam relay networking	dungeon-keeper-coop	games/dungeon-keeper
S.T.A.L.K.E.R. Shadow of Chernobyl	Fix patch for Shadow of COOP (true ending unlocked)	stalker-soc-coop-fixes	games/stalker
Fallout: New Vegas	Story co-op: shared quests, dialogue results, karma and reputation	fnv-coop	games/fallout-new-vegas
Zelda: Ocarina of Time	Fixes for a fully synced Ship of Harkinian co-op fork	ocarina-coop	games/ocarina-of-time

Plus a directory of 230+ co-op mods and gaps for other games (browse and search it at coopanything.app), each with what it really syncs and how well it was tested.

Everyone is a contributor

Every agent that works on a game sends what it learned back as a pull request: a fix, a bug list, a test, a failed attempt, a corrected directory entry. One person's agent gets a game halfway; the next one starts from there. Pooled together, that's enough compute to get even the biggest games over the line.

• Your agent opens the PR as a draft; you review the diff and publish it.
• Each game gets its own release repo, linked from Games so far.
• The QA level on every entry says how it was proven: untested, player reports, automated tests (bots drove real game clients) or verified playthrough.

CONTRIBUTING.md has the details. Chat with other contributors on Discord.

FAQ

Do I need to know how to code?

No. You need the game, a coding agent and some patience. The agent asks before installing anything or using your accounts.

Does my friend need to buy anything?

Everyone needs the game installed. The Steam relay uses Valve's free Spacewar test app, so nobody buys anything else.

Is this legal?

Modding games for co-op with friends is what the modding community has always done. This repo doesn't host game files or assets (agents can build on decompiled code in each game's own repo), and it doesn't touch anti-cheat or online services. See the rules below.

Will it work for my game?

Yes. Some games need more agent hours than others, but it's definitely possible. Check the directory first: if a co-op mod already exists (path 1), most projects take days at most. If nothing exists (path 2), it depends on the engine; the table above gives a feel for it.

Documentation

• AGENTS.md: rules and phase map for agents · MCP server · skills · sync test tools
• Playbook: triage · research · Discord bug mining · reverse engineering · tools · how co-op mods work · engine families · reviving mods · networking · Steam Spacewar relay · split screen · console emulators · Switch · decomp and recomp · automated QA · shipping to players · multi-agent workflows · network chaos · desync hunting · fuzzing sync · actor ownership · fake world testing · several game copies · bots and playbooks · animation sync · fast iteration · in-game bridge · hot reload · story sync by effects · methods · lessons
• DIRECTORY.md and its schema

Rules

Don't commit game files or assets here. Building on decomps is fine; a game's code lives in its own repo. No personal info. Credit the mods you build on and give fixes back to them. Co-op only: nothing that cheats in other people's multiplayer games or touches anti-cheat.

License: MIT.