#Git worktrees

Git worktrees are one kind of workspace.

A workspace is the place where a task happens. When that workspace is backed by a git worktree, Pier creates a separate directory on a separate branch so parallel agents never step on each other.

This page covers the git-specific details: where worktrees live, how branches are chosen, and how to configure setup hooks, scripts, terminals, and long-running services through pier.json.

#Layout and workflow

Worktrees live under $PIER_HOME/worktrees/ by default, grouped by a hash of the source checkout path. You can change the base directory with worktrees.root in config.json. Each worktree gets a random slug; the branch name is chosen when you first launch an agent.

~/.pier/worktrees/
└── 1vnnm9k3/               # hash of source checkout path
    ├── tidy-fox/           # worktree slug (branch set on first agent)
    └── bold-owl/

With a custom root, Pier keeps the same hashed layout under that directory:

{
  "worktrees": {
    "root": "/mnt/fast/pier-worktrees"
  }
}

1. Create a worktree, Pier runs your setup hooks
2. Launch an agent, a branch is created or assigned
3. Review the diff against the base branch
4. Merge or archive, archive runs teardown and removes the directory

#pier.json

Drop a pier.json in your repo root. Pier reads it from the committed version of the base branch you picked, so uncommitted changes in other branches don't apply.

{
  "worktree": {
    "setup": "npm ci",
    "teardown": "rm -rf .cache"
  },
  "scripts": {
    "test": { "command": "npm test" },
    "web": { "command": "npm run dev", "type": "service", "port": 3000 }
  }
}

#Setup and teardown

setup runs once after the worktree is created. A fresh worktree has no installed dependencies and no ignored files (like .env), so use setup to install and copy what you need. teardown runs during archive, before the directory is removed.

{
  "worktree": {
    "setup": "npm ci\ncp \"$PIER_SOURCE_CHECKOUT_PATH/.env\" .env\nnpm run db:migrate",
    "teardown": "npm run db:drop || true"
  }
}

Both fields accept a multiline shell script or an array of commands; commands run sequentially either way.

Commands run with the worktree as cwd. Use $PIER_SOURCE_CHECKOUT_PATH to reach files in the original checkout (untracked config, local caches, etc).

#Scripts and services

scripts are named commands you can run inside a worktree on demand. Mark one as a service and Pier supervises it as a long-running process, assigns it a port, and routes HTTP traffic to it through the daemon's reverse proxy.

#Plain scripts

{
  "scripts": {
    "test": { "command": "npm test" },
    "lint": { "command": "npm run lint" },
    "generate": { "command": "npm run codegen" }
  }
}

#Services

{
  "scripts": {
    "web": {
      "type": "service",
      "command": "npm run dev -- --port $PIER_PORT",
      "port": 3000
    },
    "api": {
      "type": "service",
      "command": "npm run api -- --port $PIER_PORT"
    }
  }
}

Omit port to let Pier auto-assign one. Bind your process to $PIER_PORT rather than hard-coding, each worktree gets a distinct port so multiple copies of the same service coexist.

#Reverse proxy

Every service is reachable through the daemon at a deterministic hostname:

http://<script>--<branch>--<project>.localhost:<daemon-port>

# on the default branch, the branch label is dropped:
http://<script>--<project>.localhost:<daemon-port>

*.localhost resolves to 127.0.0.1 on modern systems, so these URLs work out of the box. The proxy supports WebSocket upgrades.

#Service-to-service

Services launched from the same workspace see each other's ports and proxy URLs. Given web and api above, each process gets:

PIER_PORT=3000                         # this service's port
PIER_URL=http://web--my-app.localhost:6767  # this service's proxy URL
PIER_SERVICE_API_PORT=51732
PIER_SERVICE_API_URL=http://api--my-app.localhost:6767
PIER_SERVICE_WEB_PORT=3000
PIER_SERVICE_WEB_URL=http://web--my-app.localhost:6767

Script names are upper-cased and non-alphanumerics become _. Point your frontend at $PIER_SERVICE_API_URL instead of hard-coding a port.

#Terminals

Open terminals automatically when a worktree is created. Useful for tailing logs or leaving a REPL ready to go.

{
  "worktree": {
    "terminals": [
      { "name": "logs", "command": "tail -f dev.log" },
      { "name": "shell", "command": "bash" }
    ]
  }
}

#Environment variables

Setup, teardown, scripts, and services all see:

• $PIER_SOURCE_CHECKOUT_PATH, the original repo root
• $PIER_WORKTREE_PATH, the worktree directory
• $PIER_BRANCH_NAME, the worktree's branch
• $PIER_WORKTREE_PORT, legacy per-worktree port (prefer $PIER_PORT inside services)

Services additionally get:

• $PIER_PORT, this service's assigned port
• $PIER_URL, this service's proxy URL
• $PIER_SERVICE_<NAME>_PORT / _URL, peer service ports and URLs
• $HOST, 127.0.0.1 for local-only daemons, 0.0.0.0 when the daemon binds all interfaces

#CLI

pier run --worktree feature-auth --base main "implement auth"
pier worktree ls
pier worktree archive feature-auth