Universal Modding

Your Universal Modder first mod: a complete walkthrough

This is the whole first session, start to finish: what to pick, what the agent runs, what to check at each stage, and where sessions usually go wrong. It assumes you have already installed the toolkit — if not, the install guide is two commands for most agents.

The eight steps

  1. Pick a game and scope the first mod. Choose a single-player game you own and can reinstall, and pick the smallest interesting change: a weapon, a texture set, a new enemy or a UI tweak. Small slices are verified faster and teach the engine cheaper.
  2. Fingerprint the game with um scan. um scan finds the install across Steam, Epic and Xbox, fingerprints the engine and version, separates .NET from native code, flags anti-cheat, lists installed loaders and reports save folders, then ranks the plausible modding routes.
  3. Back up saves with um backup. um backup snapshot writes a restore point for the save folders scan reported. Do this before any agent touches the game, even for read-only projects.
  4. Pick the route and read the code. With the ranked routes in hand, the agent chooses one, fetches the relevant playbook and reads the game code only as far as the route requires — decompilation, asset extraction or loader API only.
  5. Build one working slice. The first build should be one verifiable thing end to end: the projectile spawns, the texture appears, the enemy exists. Resist adding the second feature until the slice is confirmed in game.
  6. Generate and fit assets. Art, audio and 3D come from um fal, then go through um sprite or um render3d to match the engine: cutouts, nearest-neighbour fitting, palettes, sprite sheets and team masks.
  7. Verify in the running game. um win launches the game, captures GPU-safe screenshots and can drive input that reaches only the game window. The goal is evidence from the real game, not from a compile log.
  8. Package and write the field note. um publish check blocks game files, decompiled code and leaked keys, then the mod is packaged for its platform. Finally, um kb writes a field note so the next session starts from what you learned.

Choosing the right first target

The best first game is one you know well, can reinstall from scratch, and whose modding scene has at least some public history. Games with a supported loader are easier: Terraria with tModLoader, Stardew Valley with SMAPI, Celeste with Everest. The knowledge base likely already has field notes for these, which means your agent starts with a proven route instead of reverse engineering from zero.

Avoid as a first target: anything with kernel-level anti-cheat, anything you play online competitively, and any game where a broken save would cost you hundreds of hours. The toolbox will refuse the anti-cheat cases anyway, but it is better to know the boundary before you start.

What recon tells you, and why it matters

Running um scan looks like a small thing; it is the difference between a session that works and an afternoon of guessing. The scan distinguishes a Unity game (IL-level patching with BepInEx or MelonLoader) from a native C++ game (function hooks, pattern scanning), and a .NET/XNA title (direct assembly edits) from an engine with official mod support. It also reports installed loaders and the exact save folders, so backups and edits hit the right paths on the first try.

um scan --game-path "C:\Games\YourGame"
um backup snapshot --game yourgame

If recon finds anti-cheat tied to an online mode, stop there for that title. The toolkit’s rules are explicit, and this site will not walk you around them.

Assets: generate, then fit

Generated art rarely drops straight into a game. An engine expects exact frame sizes, palettes and transparency rules — Terraria sprites are not arbitrary PNGs. The pipeline is therefore two-stage: um fal produces the art, and um sprite performs the cutout, nearest-neighbour fit, palette reduction and sheet packing the engine requires. For 3D, um render3d renders a model from the game’s camera angles into 8- or 16-heading sprite frames.

If you do not have a fal key, this step is where the session pauses — everything before it (recon, code, one working slice) still runs. Set FAL_KEY or point um comfy at a local ComfyUI server when you are ready.

Verification is the whole point

A mod that compiles is not a mod that works. um win exists so the agent can launch the game, take screenshots at the right moments, and drive input that only reaches the game window — no hijacked desktops, no stray clicks into your editor. The first slice is confirmed here, in the real game, before any scope grows.

Finishing: package, then write it down

um publish check is a hard gate: it blocks shipping game files, decompiled code and leaked API keys. After that the mod is packaged for its platform — a tModLoader build, a Fabric jar, a data-only patch — with credits in place. The last step is the one most people skip: um kb writes a field note. Five minutes of writing saves the next agent hours, whether that agent is yours or a stranger’s.

When your first mod is done, the next reading is the FAQ for the questions that come up mid-project, or the overview if you want to understand why the loop is shaped this way.