Simlock Turns Your Mac Into a Simulator Farm for Coding Agents

Running several coding agents at once is routine on web projects by now: spin up a few worktrees, let each run its own tests, and nobody steps on anybody. Mobile is where it jams. Everyone wants the same iPhone simulator; one agent is installing a build, another is tapping buttons, a third reboots it, and in the end nobody's test results can be trusted.

Simlock, open-sourced by Callstack, a long-standing React Native shop, exists to fix exactly that. It is a control plane. An agent that needs a device asks Simlock for a lease and gets back an iOS simulator, Android emulator or enrolled phone that is already booted and checked, and no other agent can touch it until it is released. When no device is free, Simlock creates one; when the machine is full, requests queue; devices nobody uses get cleaned up.

Getting started is light: install globally with npm, run simlock doctor to check the setup, then simlock lease --platform ios --device "iPhone 16" to get a device. One Mac is enough to begin. When it is not, you put more Macs and Linux machines behind a gateway that serves the whole fleet from a single URL. That is the pitch: turn your Mac into a simulator cloud that manages itself. There is a built-in web console and support for running behind an OAuth proxy, so it is clearly aimed at shared team device pools.

The physical-device handling shows real care. Phones must be enrolled by an admin before they can be leased. When an agent releases one, Simlock uninstalls the apps it added before handing it on. If a device stays offline past a grace period, the lease ends and the agent is told. Devices that are not enrolled are never touched. The details reflect a clear lesson: agents, unlike people, do not tidy up after themselves.

How the project is built is interesting too. The repo is full of rule files written for agents, and the commit history shows agents doing reviews and test audits. A tool developed heavily with agents, built specifically to serve agents, is a fair snapshot of how software gets made right now.

Mobile has been the hardest corner for AI coding: slow builds, expensive devices, messy environment state. Cloud Mac services charge by the hour. Simlock takes the other route: free, open source, and squeezing the most out of the machines you already own. For small teams and indie developers, it may be the lowest-barrier way to let several agents fix an app at the same time.