thexqin

Sim World — Development skill for Claude Code

Development community

Tiny 2D agent world in plain Node.js.

How to install Sim World

This entry records only its repository, not the path inside it, so there is no exact command to give. Open thexqin/sim-world and copy the folder into ~/.claude/skills/, or the file into ~/.claude/agents/.

What Sim World does

Tiny 2D agent world in plain Node.js. Change the rules live, save and rewind. Directed by me, written with Claude Code.

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README

Sim World

A tiny 2D world that runs on your own computer and that you watch and control from a web browser.

Small square creatures called **agents** live on a grid of grass, lakes and trees. Each one gets hungry, thirsty and tired, and has to find berries, water and rest to stay alive. You play god: change the rules of the world with dials while it runs, drop food, add creatures, and save and rewind moments in time.

No dependencies: plain Node.js and plain JavaScript, no npm install, no build step.
Everything stays in this folder. Delete the folder and it's gone.
Runs are reproducible: the same seed and the same actions always play out the same way.

Demo

https://github.com/user-attachments/assets/b5d70e3d-3839-4b3a-b2db-4938dc6e6663

How this was made

This project was written by **[Claude Code](https://claude.com/claude-code)**, Anthropic's AI coding agent.

Xiao Qin set the direction and guided the work: the idea, the design rules (no dependencies, everything local, simulation separate from display), the feature list, the build order, and what to change. Xiao also reviewed and tested every step in the browser.
Claude Code wrote the code and documentation: the simulation, server, database, browser interface, in-app Guide, and this README.

The original brief is in [CLAUDE.md](CLAUDE.md).

Requirements

Node.js 22.5 or newer. It uses Node's built-in SQLite module (node:sqlite).

Check your version with:

node --version

Getting started

git clone https://github.com/thexqin/sim-world.git
cd sim-world
node server.js

Then open **http://localhost:3000** in your browser.

Press Ctrl+C in the terminal to stop the server.
Run node server.js again to carry on exactly where you left off: the world is saved after every tick.
Need a different port? Set PORT first (PORT=3001 node server.js on macOS/Linux, $env:PORT=3001; node server.js in PowerShell).