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Co-op Anything Has AI Coding Agents Turn Single-Player Games Into Online Co-Op, Starting With the Whole Deus Ex Campaign
Co-op Anything is an MIT-licensed playbook, skill set and MCP server that tells Claude Code, Codex or another coding agent how to research, reverse engineer, test and package a co-op mod; its first release revives the 2019 HX mod so two friends can play all of Deus Ex over Steam's relay.
“Point your AI coding agent at this repo,” the Co-op Anything README says. The agent “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 whole setup is a two-line prompt for Claude Code, Codex, Gemini CLI, Cursor or OpenCode: read the repo, follow its AGENTS.md, and name the game. The repo carries the skills the agent loads, a playbook, and an MCP server that can search a directory of more than 230 existing co-op mods and detect a game’s engine from its install folder.
There are two paths. If a co-op mod already exists but is “buggy, stalled or abandoned,” the agent finds the last build, mines its bug reports, and ships fixes as a separate package. If nothing exists, it reverse engineers the game, hooks in, shows the second player and syncs enemies, world and story. Both paths end with automated tests that drive real game clients.
Deus Ex took the first path. HX, a co-op mod by Sebastian Kaufel, known as Hanfling, already turned the campaign’s conversations, missions and map travel into something Unreal Engine 1’s netcode could run. Its “last build (0.9.89.4) came out in 2019,” with known bugs still open. HX’s script package can’t be rebuilt, so the write-up says the native DLL was decompiled with Ghidra (2,773 functions) and the fixes went into a new package, HXFix, made of subclasses swapped in through HX’s own mutator hooks.
The fix list is specific: client crashes on map changes, the ending conversation that never started because a map name was compared against “NOTHING,” players arriving at a new map with 0 HP and no gear, and door codes wiped from notes on every level change. “Every fix was checked to fail with the fix turned off.”
Playing it takes Deus Ex: Game of the Year Edition from Steam or GOG, and Steam running. “The host presses 1, friends press 2, and the game connects through Steam’s relay network.” The game saves itself every time the group enters a new map. Version 0.2.0, released October 17, added save and continue.
Most game mods end where one person’s free time does. HX stopped in 2019 with its bugs listed and nobody to fix them. What’s new here is that the slow parts of finishing someone else’s mod, reading about 120,000 lines of script, decompiling a DLL and writing a test harness that launches three copies of a game, are exactly the parts a coding agent will grind through without getting bored. The human still has to own the game, review the diff and press 1.
Steam shows co-op players as “playing Spacewar,” Valve’s free test app, because that’s the relay HXCoop borrows. The README calls that “expected.” The known issues list still has one hole in the campaign: “The endgame quote and credits sequence is a stub in HX.”