coop-anything README

The project's README from github.com/cranebeaker/coop-anything. As one markdown file: README.md.

Co-op Anything

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

Support me on Ko-fi Join the Discord Browse every co-op mod on CoOp:Anything

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 · 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 coop-reverse-engineer, coop-build-from-zero, coop-networking, coop-sync-testing, 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.

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.

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

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.

coop-anything (cranebeaker/coop-anything)

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Coop-anything
What is this?Co-op Anything is an MCP server plus a playbook of skills that let an AI coding agent reverse engineer, fix, test and ship co-op multiplayer support for any single-player PC game, then package it so friends can install and join over Steam without port forwarding.
Is this a tool I run myself, or does it hand the work to my AI agent?It is not an app you run directly - it is an MCP server combined with a skills and playbook library that your coding agent (Claude Code, Codex, Gemini CLI, Cursor, OpenCode) reads and acts on to do the modding work.
Do I need special reverse-engineering tools on top of a coding agent?You need a coding agent (Claude Code, Codex, Gemini CLI, Cursor, OpenCode) and, for binary work, a reverse-engineering MCP such as REA; depending on the game's engine you may also need tools like Ghidra, Frida, Cheat Engine, BepInEx or UE4SS.
Will this definitely work for my game?Not every game is equal in effort: if a co-op mod already exists, most projects take only days, but building co-op from zero depends heavily on the game's engine and closed binaries with no existing mod are the hardest path.
Do I need to know how to code to use this?No - you just need the game installed, a coding agent, and some patience; the agent asks before installing anything or using your accounts.
Does it work on Windows, Linux and Mac, and what about couch co-op?The MCP and skills work on any PC your coding agent runs on; dedicated split-screen launchers exist for Windows (Nucleus Co-op) and Linux/Steam Deck (PartyDeck), both open source.
What are the license and rules around modding games this way?The project is MIT licensed and treats this as ordinary fan modding: it doesn't host game files or assets, doesn't touch anti-cheat or online services, and only builds co-op on top of decompiled code kept in each game's own repo.
Is modding a single-player game for co-op like this actually legal?The maintainers treat it as standard fan modding: the repo never hosts game files or assets, agents build on decompiled code that lives in each game's own separate repo, and nothing touches anti-cheat or online services.
What games already have working co-op from this project?Released examples include Deus Ex, Dungeon Keeper, S.T.A.L.K.E.R. Shadow of Chernobyl, Fallout: New Vegas, and a fully synced Zelda: Ocarina of Time, plus a searchable community directory of 230+ other co-op mods and gaps at coopanything.app.
What are the sync-test tools used for?The repo ships game-agnostic tools like 'chaos' (injects network lag/loss between real clients), 'flight' (records and auto-shrinks desyncs into regression tests), 'fuzz' (seeded multi-player invariant fuzzer) and 'ownership' (a C++ library for NPC ownership handoff) to debug co-op sync without the live game.
What are similar projects?universal-modder, rea, Reverse-Engineer-anything, mcp-gamehacking, ffmpeg-skill, stitch-skills, Kami, overmind
Which topics is it in?cheat-engine, steam-deck, steam, multiplayer, game-modding, gemini-cli, game-development, model-context-protocol, reverse-engineering, cursor, testing, mcp-server
Creator
cranebeaker
Size
1.9 MB
Stars
1.4K
Updated
CommitOct 25
Age
10d
Commits · 90 Days