Coasts Solves the Port Clash Problem Nobody Talks About but Every AI Engineer Hits

The Macro: Your Localhost Was Never Built for Parallel Agents

Here is a situation that has been getting worse all year. You have two or three AI coding agents running simultaneously on the same project. Each one is on a different git worktree because that is how you keep their changes isolated. Each worktree needs its own running instance of Postgres, Redis, your backend API, maybe a frontend dev server. And every single one of those services wants port 5432 or port 3000, because that is what is in the config.

You now have a port collision problem. And if you have ever tried to solve it manually, you know it is a nightmare of environment variable overrides, docker-compose file variants, and custom shell scripts that break the moment someone else touches the repo. I have spent entire afternoons on this exact problem and it is infuriating every time.

The standard answer from the Docker ecosystem is to run everything in separate compose stacks with custom port mappings. That works until your agents need to reference each other’s services, or until you need to hot-swap which worktree is active, or until you want to tear down one environment without affecting the other two. Docker Compose was not designed for this workflow. It was designed for single-stack orchestration.

Devcontainers exist. Remote development environments like Gitpod and Codespaces exist. But those push you off your local machine entirely. If you want to stay local (because latency matters, because your GPU is local, because you just prefer it), the tooling gap is real. Nobody built the obvious thing: per-worktree service isolation on localhost.

Until now.

The Micro: One TOML File and Your Ports Stop Fighting

Dan Hyman built Coasts after hitting this problem repeatedly while running parallel agentic workflows. He came through Y Combinator’s Fall 2025 batch, and the product is exactly as focused as it should be. It does one thing. It does it well. It is open source under MIT.

The setup is three steps. You install Coasts via a curl one-liner. You write a Coastfile in TOML that points to your existing docker-compose.yml. You run coast build and then coast run. That is it. Each worktree gets its own isolated Docker-in-Docker container with its own ports, volumes, and runtimes. No port conflicts. No manual remapping. No custom scripts.

The part I find most clever is the port naming system. Instead of hardcoding port 5432 for Postgres, you give it a logical name in your Coastfile. Coasts handles the mapping. Your application code references the logical name, and Coasts resolves it to the actual port for whichever worktree you are running. This means your docker-compose file stays clean and your agents can each have their own fully isolated stack without any of them knowing about each other.

Commands are straightforward. coast run starts an environment. coast assign maps a worktree to a Coast instance. coast exec runs commands inside a specific environment. You can have five agents, each working on a different branch in a different worktree, each with a fully running copy of your entire service stack, all on the same laptop.

The competitive landscape here is thin because most developers solve this with duct tape. Tilt handles microservice orchestration for Kubernetes dev workflows but is way heavier than what you need for local worktree isolation. DevPod offers remote dev environments. Orbstack is a faster Docker Desktop replacement but does not address the multi-worktree isolation problem specifically. Coasts occupies a niche that is small but increasingly important as agent-driven development goes mainstream.

It is also completely free. Open source, MIT licensed, no paid tier. That is either a strategic move to establish the standard before someone else does, or it is a sign that the business model has not been figured out yet. Either way, the tool works and the price is right.

The Verdict

I like this one a lot, partly because I can feel the pain it solves in my own workflow. The agentic coding pattern (multiple AI agents working on different features simultaneously) is growing fast, and every team adopting it will hit the port collision problem within the first week. Coasts is the first tool I have seen that addresses it directly without requiring you to abandon local development.

At 30 days, I want to see adoption numbers from the agentic coding community specifically. Cursor users, Cline users, Claude Code users. These are the people who will hit this wall first and hardest. At 60 days, the question is whether Coasts starts attracting feature requests that pull it toward becoming a full dev environment manager, and whether that expansion helps or hurts the product. At 90 days, I want to know if any of the bigger dev tools companies (Orbstack, Docker, the Gitpod/Codespaces crowd) start building competing features directly into their products. If they do, that validates the category. If they do not, Coasts might own this niche for a long time.

The fact that it is free and open source makes the adoption curve very different from most tools I cover here. There is no pricing friction. There is no “try it and then hit the paywall.” You install it, it works, and you either need it or you do not. For anyone running parallel agents on worktrees, you need it.