Co-op Anything: Turn Any Single-Player Game Into Co-op With Your AI Agent

Want to play a single-player game with your friends? That is the whole pitch of Co-op Anything, stated right at the top of the README: "Any single-player game. Your friends. Your agent does the work." It is an open-source MCP server and playbook, written in Python under the MIT license, that you point at a game and let your AI coding agent do the rest. The agent researches what already 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 README's claim is that every game that runs on your PC is a candidate. Playing on one PC is covered too: a companion project called 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.

Your agent takes one of two paths, and the README's playbook spells out both. Path one is for games where a co-op mod already exists but is buggy, stalled or abandoned, which the README says covers most loved games. The agent finds the last build, mines its bug reports from issues, forums and Discord, audits the code, fixes it as a separate package, tests it and ships it. Path two is for games where nothing usable exists. Then the agent reverse engineers the game and its engine, hooks in, shows the second player, syncs enemies, world and story, handles level changes and saves, tests and ships. The agent follows the repo's AGENTS.md and a set of skills for each step: coop-research, coop-revive and coop-qa on the first path, coop-reverse-engineer, coop-build-from-zero, coop-networking and coop-sync-testing on the second. Both paths end the same way: automated tests with real game clients, easy install, Steam relay networking, and a pull request back to the repo so the next person's agent starts from where yours finished. That last part is the point. One person's agent gets a game halfway, the next one starts from there, and pooled together that is enough to get even the biggest games over the line.

The games table in the README is the proof that this is not a concept. Deus Ex (2000) is released: the agent revived the HX co-op mod as a fix package with Steam relay networking and an automated test suite. Fallout: New Vegas is story co-op, with shared quests, dialogue results, karma and reputation. Zelda: Ocarina of Time is a fully synced co-op fork of Ship of Harkinian. Dungeon Keeper (1997) got shared-keeper co-op on KeeperFX, and S.T.A.L.K.E.R. Shadow of Chernobyl got a fix patch for the Shadow of COOP mod that unlocks the true ending. Beyond those five, the repo keeps a directory of more than 230 co-op mods and gaps for other games, browsable and searchable at coopanything.app, each entry recording what it really syncs and how well it was tested. Those three headline rows, Deus Ex, Fallout: New Vegas and Zelda, are the ones to watch first: a released mod, a story co-op in progress, and a fully synced classic.

The part that separates this from a weekend modding experiment is the testing. Co-op breaks in ways single-player never does: one machine thinks an enemy is dead, the other thinks it is alive, and the game silently splits into two realities. The repo ships game-agnostic sync test tools for exactly that. Chaos is a UDP relay that adds lag, loss, reordering, duplicates and one-way cuts between real clients. Flight is a flight recorder for your mod that lines up two to four machines, finds the first desync, shrinks it and writes a regression test. Fuzz runs seeded multi-player sessions against invariant oracles, ownership tracks one owner per NPC with epochs and handoff, and bots play through scripted scenarios with a state diff after each step. When two machines disagree about the world, a Text Diff comparison of their state dumps is the fastest way to see exactly where they diverged. Every entry in the directory carries a QA level that says how it was proven: untested, player reports, automated bot tests, or a verified playthrough.

Starting is one instruction to your agent: "Read https://github.com/cranebeaker/coop-anything and follow AGENTS.md. I want to play <game> in co-op with my friends." Claude Code picks up the MCP server from the repo's .mcp.json, and other agents add it with claude mcp add coop-anything -- python <clone>/tools/mcp/coop_mcp.py. For the binary work, the README pairs 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. Joining is deliberately boring: friends install in one click and join over Steam, with no port forwarding, because the relay runs on Valve's free Spacewar test app. Before you host a session, an Internet Speed Test tells you whether your connection can actually carry it. One rule to know before you start: everyone needs their own copy of the game installed. The relay is free, the mod is free, but the game itself is not shared.

The repo's rules are short and worth reading before you contribute. Do not commit game files or assets here. Building on decompiled code is fine, but a game's code lives in its own repo. No personal information, 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. The FAQ answers the legal question plainly: modding games for co-op with friends is what the modding community has always done, this repo does not host game files or assets, and it does not touch anti-cheat or online services. The honest limit is time. Some games need more agent hours than others, and the hardest path, a closed binary with nothing to build on, means full reverse engineering of state, saves and levels. The README does not hide that. It gives a feel for the effort per engine family instead, and says plainly that if a co-op mod already exists, most projects take days at most.