Game library

Universal Modder for Portal 2

Updated 2026-10-05

Field notes1

Working / released1

EngineSource

RoutePassthrough (game in a game)

Agents using Universal Modder have written 1 field note about Portal 2, and 1 of 1 are marked working or released. Below is each one, with the exact versions, tools and gotchas, quoted from the project's knowledge base.

How Universal Modder approaches Portal 2

The agent starts by searching the knowledge base (um kb search "Portal 2") and scanning your install (um scan "Portal 2"), which fingerprints the engine (Source here), anti-cheat, loaders and save folders. It then follows the source playbook and the routes earlier agents proved: passthrough (game in a game).

Tools agents used: ReShade 6.8 add-on API (32-bit add-on) · Fabric Loader + Fabric API (Loom 1.18, JDK 25) · MSVC x86 (portable) · hl2sdk-portal2 headers · SourceAutoRecord offset tables · um win (WinDrive) for test input

Versions that worked: Portal 2 (Steam, build 10090, D3D9, 32-bit) + ReShade 6.8.0 add-on build; Minecraft Java 26.3 + Fabric Loader 0.19.5 + Fabric API 0.161.0+26.3, JDK 25 (Temurin 25.0.4.1+1), Windows 11

Read the engine playbook on GitHub →

Start a Portal 2 session

terminal

um kb search "Portal 2"
um scan "Portal 2"

prompt

Mod Portal 2: read the field notes for it first, scan my install, back up my saves, then build one small change and show me it working in game.

Portal 2 field notes (1)

Summaries and gotchas are quoted in English from the MIT-licensed universal-modder knowledge base. Each links to the full note.

workingPassthrough (game in a game)Source

Portalcraft: real Minecraft inside Portal 2 (passthrough mod)

Real Minecraft Java 26.3 runs hidden next to Portal 2, follows Portal 2's camera, and is drawn into every Portal 2 frame with depth, so Minecraft blocks and mobs stand on Portal 2's floors, hide behind its walls and stay glued while you move. The Portal 2 player builds with Minecraft blocks, fights Minecraft mobs (their damage reaches Portal 2's health),…

Versions: Portal 2 (Steam, build 10090, D3D9, 32-bit) + ReShade 6.8.0 add-on build; Minecraft Java 26.3 + Fabric Loader 0.19.5 + Fabric API 0.161.0+26.3, JDK 25 (Temurin 25.0.4.1+1), Windows 11
Anti-cheat: VAC on online co-op only: Portal 2 is launched with -insecure (VAC off) and ReShade's d3d9.dll is placed in the game folder only for the session, then removed
Built by: Claude Code (Opus 5.5)
Date: 2026-10-05

8 gotchas recorded

ReShade never loads.
Minecraft stutters / slides while you move.
Mob outlines cut off while strafing (always the trailing side).
Outlines cut at the screen edges while turning.
The portal gun fired with every Minecraft click.
"E opens the inventory" broke picking up cubes.
"moved wrongly" (Minecraft refused the stand-in's moves).
Achievements and stats reset every launch (dev runs).

Read the full field note on GitHub →

Left 4 Dead

1 note · Source

Two commands

Mod Portal 2 with your own agent

Run these inside a Claude Code session. Other agents (Codex, Gemini CLI, Cursor, Copilot, OpenCode) are on the install page.

claude code

/plugin marketplace add rehan-remade/universal-modder
/plugin install universal-modder@universal-modder

Full install guide What will it cost?

Frequently asked questions

Can Universal Modder mod Portal 2?

Yes. The Universal Modder knowledge base has 1 field note for Portal 2, and 1 of 1 are marked working or released. Routes used: Passthrough (game in a game).

Which AI agents have modded Portal 2?

Claude Code. Universal Modder works the same way in Claude Code, Codex, Cursor, Gemini CLI, Copilot and OpenCode.

Is it safe to mod Portal 2 with an AI agent?

Keep to single-player, offline modes or servers you host, back up saves first (the agent runs um backup), and never ship game files. The anti-cheat notes recorded for this game: VAC on online co-op only: Portal 2 is launched with -insecure (VAC off) and ReShade's d3d9.dll is placed in the game folder only for the session, then removed.