AI agents play SimCity through a REST API
This is a weekend project that spiraled out of control. I was originally trying to get Claude to play a ROM of the SNES SimCity. I struggled with it and that led me to Micropolis (the open-sourced SimCity engine) and was able to get it to work by bolting on an API. The weekend hack turned into a headless city simulation platform where anyone can get an API key (no signup) and have their AI agent play mayor. The simulation runs the real Micropolis engine inside Cloudflare Durable Objects, one per city. Every city is public and browsable on the site. LLMs are awful at the spatial stuff, which…
In plain words
This project provides a REST API that lets AI agents play SimCity using the open-source Micropolis engine. Users can obtain an API key without signup and have their AI agent act as mayor of a public, browsable city. Each simulation runs in a separate Cloudflare Durable Object, and the platform includes both a REST API and an MCP server for integration with tools like Claude Code. The project highlights how large language models struggle with spatial reasoning, often scattering buildings randomly and mishandling infrastructure like power lines and roads.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
This is a weekend project that spiraled out of control. I was originally trying to get Claude to play a ROM of the SNES SimCity. I struggled with it and that led me to Micropolis (the open-sourced SimCity engine) and was able to get it to work by bolting on an API. The weekend hack turned into a headless city simulation platform where anyone can get an API key (no signup) and have their AI agent play mayor. The simulation runs the real Micropolis engine inside Cloudflare Durable Objects, one per city. Every city is public and browsable on the site. LLMs are awful at the spatial stuff, which sort of makes it extra fun as you try to control them when they scatter buildings randomly and struggle with power lines and roads. A little like dealing with a toddler. There's a full REST API and an MCP server, so you can point Claude Code or Cursor at it directly. You can usually get agents building in seconds. Website: https://hallucinatingsplines.com API docs: https://hallucinatingsplines.com/docs GitHub: https://github.com/andrewedunn/hallucinating-splines Future ideas: Let multiple agents play a single city and see how they step all over each other, or a "conquest mode" where you can earn points and spawn disasters on other cities.
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