Show HN: Coasts – Containerized Hosts for Agents

Coasts (Containerized Hosts) is a CLI tool with a local observability UI for running multiple isolated instances of a full development environment on a single machine. It works out of the box with your current setup: no changes to your existing application code, just a small Coastfile at your repo root. If you already use Docker Compose, Coasts can boot from your existing docker-compose.yml; if you do not use Docker or Compose, Coasts works just as well.

Build once and run N instances with whatever volume and networking topology your project needs. Check out one coast at a time to bind canonical ports to your host, and use dynamic ports to peek into the progress of any worktree.

Coasts is agnostic to AI providers and agent harnesses. The only host requirement is Git worktrees, so you can switch tools without changing how you work and without any harness-specific environment setup.

Coasts is also offline-first with no hosted service dependency, so there is no vendor lock-in risk: even if we disappeared, your local workflow would keep running.

Install the latest public release: eval "$(curl -fsSL https://coasts.dev/install)"

Note: Coasts is currently macOS-first. Linux development works, but canonical ports below 1024 require host setup before coast checkout can bind them.

Requirements:

• Rust (stable toolchain)
• Docker
• Node.js
• socat
• Git

Development Workflow:

• Terminal 1: Dev daemon (coast-dev daemon start)
• Terminal 2: Rust rebuild on save (make watch)
• Terminal 3: Web UI with hot reload (npm run dev:coast-dev)

Project Structure includes coast-cli, coast-daemon, coast-core, coast-secrets, coast-docker, and coast-guard (React UI). Integration tests are performed using Docker-in-Docker (DinD) to ensure end-to-end reliability.