I'm working on a 3D town where AI agents live as NPCs with daily routines. Early on I realized if people can't customize the town, they don't care about it. So I built a browser-based map editor.

Github：https://github.com/Agentshire/Agentshire

Things that worked:

* Sharing the renderer between editor and game. Preview isn't a separate build, it's the same scene with game systems turned on. This cut iteration time way down.
* Keeping it drag-and-drop simple. No scripting, no node graphs. Place buildings, move them around, done. The complexity lives in the NPC behavior, not the editor.

Things I'd do differently:

* Should have built the editor first. I hand-placed everything for months before making this, and rebuilding layouts after having an editor made me throw out most of my original work.
* Undo/redo for grouped objects is harder than it sounds. I went through three implementations before landing on a command pattern with full transform snapshots.

The NPCs run on a state machine with weighted destination scoring (affinity + crowding + recency penalties) and 400+ preset dialogues, with an optional LLM layer on top. But the editor is what made people actually want to try it, nobody cared until they could make it theirs.

Open source, link in comments.

I built a map editor for my AI NPC town so players could design their own — here's what I learned