Editor guide

The editor is where every part of a game is authored. It runs in your browser, and everything you change is checked as you work.

Workspaces

The buttons along the top switch between seven workspaces.

A file list on the left opens anything by name. The bottom panel shows the build output, a list of problems, and how full the ROM is.

Build a room

A room has a walkable area, a floor, walls and furniture. You place models from the library, add lights, and put the player in. Each view of a room is a camera.

Press Bake on a camera. The preview shows the picture the Game Boy will show: at most 4 colours per 8 by 8 tile. If something does not fit, the checker says what and where, and highlights it in the preview.

Doors and triggers

A door is a model with a trigger area. Link it to another room and choose where the player appears there. A door can play an opening animation, which you edit as a door look in Assets, and it can be locked at the start of the game.

A trigger is a named set of floor cells. Stepping on it runs a script. Triggers are how a game reacts to the player.

Items

Items are things the player can carry. Each has a short name, a stack limit and a 16 by 16 icon drawn in a palette of three colours shared by every icon.

Place a pickup in a room to put an item on the floor. The player picks it up with A. A locked door opens when a script unlocks it, for example once the player holds a key.

Screens

The Screens workspace holds the screen graph: the title, menus, options, character select, pause and inventory screens, and the wires between them. Pick a start screen, and choose which screen opens on SELECT and which on START. You draw each screen's background as an image and place its text, buttons and toggles on top.

Sound

The Sound workspace holds a game's songs, sound effects and instruments. Songs have four lanes, one per Game Boy sound channel, and a piano roll. Effects start from one-click presets that you can tweak. Pick a song for each room and screen, and sounds for doors, triggers and menus.

Build and play

Press ▶. The editor builds the ROM and runs it in the Play workspace, with sound and the same controls as the examples. Tick DMG first to run it as a Game Boy would. Download ROM saves the file for an emulator or a flash cart.

If the checker finds an error, the build stops and Problems lists each one. Warnings do not stop it. Click a problem to jump to the thing it is about.

The Assistant

The Assistant workspace lets you describe a change in plain words: add a room called cellar with a door from the hall. Claude makes the same edits you would make by hand, and the checker validates them the same way.

It works through your own Claude Code login. Install Claude Code and sign in once; the editor never asks for an API key and stores no credential. Until you are signed in, the Assistant tab stays hidden. Usage counts against your own Claude plan.

In Ask first mode, Claude's edits wait as a proposal you can Apply or Discard. In Just do it mode they apply when the turn ends. Undo last takes back the latest batch.