cranebeaker/coop-anything

What it claims

Co-op Anything is a playbook, skill set and MCP server for coding agents that add co-op to single-player games. Its own releases cover five games: Deus Ex (2000), Dungeon Keeper (1997), S.T.A.L.K.E.R. Shadow of Chernobyl, Fallout: New Vegas and Zelda: Ocarina of Time. Each has its own release repo and write-up. The repo also keeps a directory of 230+ co-op mods and gaps, searchable at coopanything.app. Each entry records what the mod really syncs and how well it was tested. The page lists community projects including Mega Man X, Pilotwings 64, Enter the Gungeon, Command & Conquer 3 and Modern Warfare 2 campaign co-op.

How it works

The agent picks one of two paths. Both end in the same steps: QA, packaging, Steam relay networking and a pull request.

flowchart TD
  A[Search co-op directory] --> B{Usable mod exists?}
  B -->|Buggy or abandoned| C[Path 1: mine bug reports, audit, fix as separate package]
  B -->|Nothing usable| D[Path 2: reverse engineer, hook, sync enemies, world, story, saves]
  C --> E[Automated QA with bots in real clients]
  D --> E
  E --> F[One-click install, Steam relay]
  F --> G[Draft PR back to repo]

Path 1 uses the coop-research, coop-revive, coop-qa and couchlink skills. Path 2 adds coop-reverse-engineer, coop-build-from-zero, coop-networking and coop-sync-testing. The page puts Path 1 projects at "days at most". Path 2 time depends on the engine.

An engine table maps game types to approaches:

• Multiplayer engines (Unreal 1/2, Source, id Tech, X-Ray): script mods on the existing netcode.
• Bethesda (Gamebryo, Creation): xNVSE, SKSE or F4SE plugins with host authority.
• Unity: BepInEx or MelonLoader with Harmony patches.
• Unreal Engine 4/5: UE4SS and Dumper-7.
• Proprietary engines: DLL hooks via MinHook or REFramework.
• Decomps and source ports: networking added directly in the code.
• Console-only games: a decomp or recompiled port (N64Recomp, XenonRecomp), otherwise emulator netplay or memory sync via PCSX2 PINE, Dolphin Memory Engine or BizHawk/mGBA Lua.
• Closed binaries with nothing else: full reverse engineering with REA, GhidraMCP, ida-pro-mcp, Frida and Cheat Engine. The page calls this the hardest path.

Networking uses Valve's free Spacewar test app as a Steam relay, so players need no port forwarding and buy nothing beyond the game. Split screen on one PC goes through Couchlink. Couchlink builds on Nucleus Co-op (Windows) and PartyDeck (Linux, Steam Deck) and runs one game copy per player.

The tools/ directory is game-agnostic and came out of the fnv-coop project. Each tool has tests, mutation twins and a single command that prints ALL OK.

• chaos: a UDP relay that adds lag, loss, reordering, duplicates and one-way cuts.
• flight: aligns logs from 2 to 4 machines, finds the first desync, shrinks it and writes a regression test.
• fuzz: a seeded N-player fuzzer with invariant oracles (converge, no double apply, one owner, no dupes, nothing stale).
• ownership: a C++ library for one owner per NPC, with epochs, handoff and stale echo rejection.
• hotreload: swaps a mod's core inside running games.

How to use it

Prompt the 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 loads the MCP server from the repo's .mcp.json. For other clients:

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

Setup for Codex, Gemini CLI and Cursor is in playbook/mcp.md. For binary work the page pairs the server with the REA reverse-engineering MCP:

npx rea-agents setup

Run all sync-tool tests with:

python -I tools/test_all.py

Limits

Directory entries carry a QA level: untested, player reports, automated tests (bots drove real game clients) or verified playthrough. Check that level before relying on an entry. Agent PRs open as drafts for human review. Rules forbid committing game files or assets and anything that touches anti-cheat or other people's multiplayer. The repo hosts no game files, and decompiled code lives in each game's own repo. Every player must own the game. The claim that any game can be made co-op is the project's own assertion. The page gives no measured agent hours or success rates for Path 2. The repo is MIT-licensed.