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.
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 · S.T.A.L.K.E.R. Clear Sky
From the community: Mega Man X and Mega Man X4 (native PC with co-op netplay) · Pilotwings 64 (split-screen) · Zelda: Oracle of Seasons (in progress) · yours next? Community tools: DecompPipeline (agent-driven decompilation of console games, Dreamcast first).
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 |
coop-reverse-engineer, coop-build-from-zero, coop-networking, coop-qa |
| 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.
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 / Clear Sky | Fix patch for Shadow of COOP (true ending unlocked); finishing Clear COOP in progress | stalker-soc-coop-fixes (SoC); Clear Sky coming soon | 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.
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.
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 their own copy of the game. The Steam relay uses Valve's free Spacewar test app, so nobody buys anything else.Is this legal?
Modding games you own for co-op with friends is what the modding community has always done. This repo never contains game files, cracks or decompiled source of closed games, and it does not 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
- 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 · methods · lessons
- DIRECTORY.md and its schema
Rules
Own the games. No game files, cracks or decompiled closed source in this 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.