Show HN: We started building an AI dev tool but it turned into a Sims-style game

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154 points by maxraven 3 days ago


Hi HN! We’re Max and Peyton from The Interface (https://www.theinterface.com/).

We started out building an AI agent dev tool, but somewhere along the way it turned into Sims for AI agents.

Demo video: https://www.youtube.com/watch?v=sRPnX_f2V_c.

The original idea was simple: make it easy to create AI agents. We started with Jupyter Notebooks, where each cell could be callable by MCP—so agents could turn them into tools for themselves. It worked well enough that the system became self-improving, churning out content, and acting like a co-pilot that helped you build new agents.

But when we stepped back, what we had was these endless walls of text. And even though it worked, honestly, it was just boring. We were also convinced that it would be swallowed up by the next model’s capabilities. We wanted to build something else—something that made AI less of a black box and more engaging. Why type into a chat box all day if you could look your agents in the face, see their confusion, and watch when and how they interact?

Both of us grew up on simulation games—RollerCoaster Tycoon 3, Age of Empires, SimCity—so we started experimenting with running LLM agents inside a 3D world. At first it was pure curiosity, but right away, watching agents interact in real time was much more interesting than anything we’d done before.

The very first version was small: a single Unity room, an MCP server, and a chat box. Even getting two agents to take turns took weeks. Every run surfaced quirks—agents refusing to talk at all, or only “speaking” by dancing or pulling facial expressions to show emotion. That unpredictability kept us building.

Now it’s a desktop app (Tauri + Unity via WebGL) where humans and agents share 3D tile-based rooms. Agents receive structured observations every tick and can take actions that change the world. You can edit the rules between runs—prompts, decision logic, even how they see chat history—without rebuilding.

On the technical side, we built a Unity bridge with MCP and multi-provider routing via LiteLLM, with local model support via Mistral.rs coming next. All system prompts are editable, so you can directly experiment with coordination strategies—tuning how “chatty” agents are versus how much they move or manipulate the environment.

We then added a tilemap editor so you can design custom rooms, set tile-based events with conditions and actions, and turn them into puzzles or hazards. There’s community sharing built in, so you can post rooms you make.

Watching agents collude or negotiate through falling tiles, teleports, landmines, fire, “win” and “lose” tiles, and tool calls for things like lethal fires or disco floors is a much more fun way to spend our days.

Under the hood, Unity’s ECS drives a whole state machine and event system. And because humans and AI share the same space in real time, every negotiation, success, or failure also becomes useful multi-agent, multimodal data for post-training or world models.

Our early users are already using it for prompt-injection testing, social engineering scenarios, cooperative games, and model comparisons. The bigger vision is to build an open-ended, AI-native sim-game where you can build and interact with anything or anyone. You can design puzzles, levels, and environments, have agents compete or collaborate, set up games, or even replay your favorite TV shows.

The fun part is that no two interactions are ever the same. Everything is emergent, not hard-coded, so the same level played six times will play out differently each time.

The plan is to keep expanding—bigger rooms, more in-world tools for agents, and then multiplayer hosting. It’s live now, no waitlist. Free to play. You can bring your own API keys, or start with $10 in credits and run agents right away: www.TheInterface.com.

We’d love feedback on scenarios worth testing and what to build next. Tell us the weird stuff you’d throw at this—we’ll be in the comments.

pizzathyme - 3 days ago

I worked on The Sims. From experience I can tell you these types of games require a ton of experimentation and building before you finally hit on something that feels "fun" and you get lost in playing it. Then it all kind of comes together at once.

Keep it up! Looking forward to what you figure out.

OtherShrezzing - 3 days ago

I’ve been thinking about how traditional game AI can be improved by generative models. One of the biggest problems with games like Civ is that the AI strategy is predictable - especially if you’ve played a few dozen hours.

LLMs with some decent harnesses could build up unpredictable - but internally consistent - strategies per each new game you play.

This is close to a proof of concept for those improvements.

xrd - 3 days ago

I find this funny because Stewart Butterfield (and others) founded Slack and Flickr by pivoting from the games they were trying to build. This is the opposite, someone trying to build a product and then pivoting to a game. I think this is a better path, FWIW.

splatzone - 3 days ago

I’ve felt for some time that there’s a gap in the market for a genuine spiritual successor to The Sims, using LLMs to power the interactions between agents to create a more realistic and immersive simulation of life. This seems like a step in the right direction.

saberience - 3 days ago

What's the actual gameplay loop?

I.e. what's the goal, how do you know you're doing well (or not), what makes it fun etc?

indigodaddy - 3 days ago

This is cool for sure. Is it only all about tiles? Lately I've been thinking it would be awesome to get an AI to play DXBall (bricks game) type game or perhaps lode runner etc. would that be doable here?

thatha7777 - 3 days ago

Kudos, this is a very novel take! What's the most surprising emergent behavior you've observed? Have you observed any "social dynamics" that you didn't explicitly program?

_pdp_ - 3 days ago

The reason text works is because it has higher bit rate then speech. This is way many believe that CLI tools are still considered supreme in terms of getting things done quick.

While fun this game-like interface is too casual and it certainly has lower bit rate which impacts communicate exchange between an AI and the human operator.

It will be a fine abstraction if the goal is to have high-level overview though.

soared - 3 days ago

I wonder if this would be good for vibe coding / natural language for enemy AI. IE, place an enemy down and tell it: “every 3 seconds fire an arrow at the player. If the player is within 7 tiles of you, stop firing arrows, path to the player, and attack it with a sword. When your health reaches 10% run away from the player”

NietzscheanNull - 3 days ago

Just a heads up: the signup form disclaimer ("by signing up to create an account, you are accepting our terms of service and privacy policy") appears to link to a ToS route (theinterface.com/terms), but clicking that immediately redirects back to the login page (/signin) on Firefox [141.0.3].

Same thing happened when I tried hitting the URL directly. Do I have to accept the ToS before I'm allowed to read it?

- 2 days ago
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bennymag - 3 days ago

I think this would be a great learning tool too - imagine like a bridge simulator or robocodo (https://game.rodocodo.com/hour-of-code/) - which is a learn to code tool for elementary students - but for AI agents. As a tribute to Sims, you should allow for the `rosebud` cheat code :)

polotics - 3 days ago

Have you gotten inspired by the Black Mirror "Plaything" episode? :-D

- 2 days ago
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lzyuan1006 - 2 days ago

Expecting good things to happen, I prefer games like The Sims

jader201 - 3 days ago

PSA: In case you don't realize, this video has commentary. But it's crazy low, and you have to turn your volume way up to hear it.

I thought it was just another YouTube video with no audio.

Federt231 - 2 days ago

Haker

gnerd00 - 3 days ago

this has carefully costumed role playing characters in the first second -- the title is misleading and/or "con"

insamniac - 3 days ago

Not supported on linux :(

mxwilliamson99 - 3 days ago

Pretty cool

skyzouwdev - 3 days ago

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bakugo - 3 days ago

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rtd_rosuu_23 - 2 days ago

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monster_truck - 3 days ago

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