Turn any single player PC game into coop instantly

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.

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 · yours next?

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).

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.

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.

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).

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

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.

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, each with what it really syncs and how well it was tested.

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.

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

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 · multi-agent workflows · network chaos · desync hunting · fuzzing sync · actor ownership · fake world testing · several game copies · bots and playbooks · animation sync · 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.