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, Codius 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 codius.json.

Layout and workflow

Worktrees live under $CODIUS_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 slug and a branch when its workspace is created.

~/.codius/worktrees/
└── 1vnnm9k3/               # hash of source checkout path
    ├── tidy-fox/           # worktree slug
    └── bold-owl/

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

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

1. Create a workspace with worktree isolation, Codius creates the worktree and runs your setup hooks
2. Launch one or more agents in that workspace
3. Review the diff against the base branch
4. Merge or archive the workspace; after the last workspace using it is archived, Codius runs teardown and removes the worktree

Create a worktree-backed workspace

The examples below use the current directory as the source checkout. Pass --path ~/dev/my-app to create the workspace from another checkout.

Branch off from a base branch:

codius workspace create \
  --isolation worktree \
  --mode branch-off \
  --new-branch feature/auth \
  --worktree-slug feature-auth \
  --base main

Check out an existing branch:

codius workspace create \
  --isolation worktree \
  --mode checkout-branch \
  --branch feature/existing \
  --worktree-slug existing-copy

Or open a pull request in its own workspace:

codius workspace create \
  --isolation worktree \
  --mode checkout-pr \
  --pr-number 2186

Add --forge <name> when Codius cannot infer the forge from the source checkout.

codius.json

Drop a codius.json in your repo root. Codius 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 \"$CODIUS_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 $CODIUS_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 Codius supervises it as a long-running process, assigns it a port, and routes HTTP traffic to it through the daemon's reverse proxy.

Run them from the app, or manage them from automation with codius script and the workspace-script MCP tools.

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 $CODIUS_PORT",
      "port": 3000
    },
    "api": {
      "type": "service",
      "command": "npm run api -- --port $CODIUS_PORT"
    }
  }
}

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

Dynamic port allocation

By default, Codius asks the OS for an available ephemeral port. Configure a range globally in ~/.codius/config.json or per project in codius.json:

// ~/.codius/config.json
{
  "worktrees": {
    "servicePorts": { "range": "3000-4000" }
  }
}

// codius.json
{
  "worktree": {
    "servicePorts": { "range": "3000-4000" }
  }
}

The range is inclusive. A project servicePorts block replaces the global block. An explicit service port always wins over either setting.

For an external allocator, configure portScript instead:

{
  "worktree": {
    "servicePorts": { "portScript": "/usr/bin/portmake" }
  }
}

Codius runs the executable in the workspace directory with four arguments: service name, workspace ID, branch name, and worktree path. Since the script is executed directly without a shell, portScript must point to a real executable (such as a compiled binary or a script with a proper shebang line like #!/bin/bash) rather than an inline shell command or pipeline. If you need shell evaluation or pipelines, wrap them in a small executable script. A missing branch is passed as an empty string. The same values are available as CODIUS_SCRIPTNAME, CODIUS_WORKSPACE_ID, CODIUS_BRANCH_NAME, and CODIUS_WORKTREE_PATH. It must print one valid TCP port to stdout. portScript wins over range in the same block. Codius trusts the external allocator, so the returned port may already be in use, for example by a service Codius will attach to.

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:

CODIUS_PORT=3000                         # this service's port
CODIUS_URL=http://web--my-app.localhost:6767  # this service's proxy URL
CODIUS_SERVICE_API_PORT=51732
CODIUS_SERVICE_API_URL=http://api--my-app.localhost:6767
CODIUS_SERVICE_WEB_PORT=3000
CODIUS_SERVICE_WEB_URL=http://web--my-app.localhost:6767

Script names are upper-cased and non-alphanumerics become _. Point your frontend at $CODIUS_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:

• $CODIUS_SOURCE_CHECKOUT_PATH, the original repo root
• $CODIUS_WORKTREE_PATH, the worktree directory
• $CODIUS_BRANCH_NAME, the worktree's branch
• $CODIUS_WORKTREE_PORT, legacy per-worktree port (prefer $CODIUS_PORT inside services)

Services additionally get:

• $CODIUS_PORT, this service's assigned port
• $CODIUS_URL, this service's proxy URL
• $CODIUS_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

Manage the workspace

codius workspace ls
codius run --workspace <workspace-id> "implement auth"
codius workspace archive <workspace-id>

For the common case, codius run --new-workspace worktree --worktree-mode branch-off --new-branch feature/auth --base main "implement auth" creates both the workspace and its first agent.