Udderly instant workspaces.

yes, it's called cow. as in Copy-On-Write. we have no regrets.

Clone your entire git repo — node_modules, build outputs, .env files and all — in milliseconds with near-zero disk overhead. Point an AI coding agent at each workspace and let them work in parallel.

How it works GitHub Docs

🍎 macOS · APFS ⚡ millisecond clones 💾 near-zero disk overhead 🦀 written in Rust 🤖 AI-agent ready 🆓 MIT licence

the alternatives

Every other approach is udderly wrong.

Running multiple AI coding agents in parallel means multiple isolated workspaces. Here is what you are up against otherwise.

🌿

git worktrees

Shares the object store but not node_modules, build artefacts, or .env files. Every new worktree needs a full npm install. Agents step on each other's lock files. Works at a small scale; falls apart fast.

✗ doesn't scale

📦

full clone

Copying 2 GB of node_modules four times over takes minutes and burns 8 GB of disk. You will run df -h with increasing alarm. Also slow to delete when you are done.

✗ slow and disk-hungry

🐳

containers / VMs

Heavyweight. Minutes to spin up. No native macOS toolchains. Your Xcode build does not work in a Linux container. Neither does your iOS simulator. Wrong layer of abstraction entirely.

✗ wrong layer of abstraction

the solution

Copy-On-Write, from the filesystem up.

APFS has had block-level CoW cloning since macOS High Sierra. cow just wires it up with a nice interface.

Clone with `clonefile(2)`

Uses the same syscall Time Machine uses. A byte-identical copy of your entire repo directory in one call. No data is physically duplicated on disk until a file actually changes.

Checkout or create a branch

Optionally check out an existing branch or create a new one in the workspace. It is a fully independent git repo with its own HEAD, index, and working tree.

Clean up runtime artefacts

Removes .pid, .sock, and .socket files that should not be shared between workspaces. Reads .cow.json for project-specific cleanup rules and post-clone commands.

Point your agent at it

Each workspace lands in ~/.cow/workspaces/{name}. Open Claude Code, Cursor, or Aider in each one. They work in complete isolation until you extract their changes.

cli reference

Five commands. That is the whole thing.

Deliberately minimal. No config files to maintain, no daemons to manage, no subscriptions.

# Create a named workspace on a new branch $ cow create feat-auth --source ~/my-project --branch feat/auth ✓ Detected APFS filesystem ✓ Detected git repository Cloning via APFS copy-on-write… ✓ Cloned in 41ms ✓ Created branch 'feat/auth' ✓ Created workspace 'feat-auth' → ~/.cow/workspaces/feat-auth # Omit the name and it auto-generates agent-1, agent-2, … $ cow create --source ~/my-project ✓ Created workspace 'agent-1' → ~/.cow/workspaces/agent-1

$ cow list NAME BRANCH STATUS CREATED ─────────── ──────────────── ───────── ────────────── agent-1 feat/auth clean 5 minutes ago agent-2 feat/api dirty 8 minutes ago feat-auth feat/auth clean 12 minutes ago # JSON output for scripts and MCP tools $ cow list --json [{"name":"agent-1","branch":"feat/auth","vcs":"git",…}]

# Interactive: prompts if workspace has uncommitted changes $ cow remove agent-2 Workspace 'agent-2' has uncommitted changes. Remove anyway? [y/N]: y ✓ Removed workspace 'agent-2' # --force skips the prompt entirely $ cow remove --force agent-1 feat-auth ✓ Removed workspace 'agent-1' ✓ Removed workspace 'feat-auth' # Remove all workspaces from a given source repo $ cow remove --all --force --source ~/my-project

# Export changes as a patch file $ cow extract agent-2 --patch ~/auth-changes.patch ✓ Wrote patch to ~/auth-changes.patch # Or push the branch to origin for a PR $ cow extract agent-2 --branch feat/auth-review Pushing 'feat/auth-review' to origin… ✓ Branch pushed to origin/feat/auth-review # Then clean up the workspace $ cow remove --force agent-2

$ cow status agent-2 Workspace: agent-2 Path: ~/.cow/workspaces/agent-2 Source: ~/my-project VCS: git Branch: feat/api Status: dirty Created: 8 minutes ago M src/api/routes.rs A src/api/middleware.rs # Also works from inside a workspace directory $ cd ~/.cow/workspaces/agent-2 && cow status

comparison

cow 🐄 vs the alternatives.

Spoiler: the one named after a farm animal wins on every metric that matters for parallel AI development.

Feature	cow 🐄	git worktree	full clone
Clone time (2 GB repo)	~40ms	~1s (no modules)	3–8 minutes
Extra disk per workspace	~0 until modified	~0 (no modules)	full copy × N
node_modules included	✓	✗	✓
Isolated .env files	✓	✗ (shared)	✓
Build artefacts included	✓	✗	✓
Independent git history	✓	✓	✓
macOS native toolchains	✓	✓	✓
jj (Jujutsu) support	✓	n/a	manual
MCP server built in	✓	✗	✗
Platform requirement	macOS + APFS	any OS	any OS

ai integration

A first-class MCP server.

Run cow mcp to expose workspace management as MCP tools. Your AI orchestrator can create and tear down workspaces without shelling out.

Add to Claude Code

Drop this snippet into your ~/.claude/claude.json or a project-local .claude/claude.json to let Claude manage its own workspaces on your behalf.

Exposes four MCP tools: cow_create, cow_list, cow_remove, cow_status.

Communicates over stdio — no ports, no background daemons, no port conflicts.

// ~/.claude/claude.json
{
  "mcpServers": {
    "cow": {
      "command": "cow",
      "args": ["mcp"]
    }
  }
}

get started

Ready to join the herd?

macOS with APFS required. Apple Silicon and Intel both supported via a universal binary.

🍺 Homebrew

# Add the tap once
brew tap joeinnes/tap

# Install cow
brew install cow

# Verify
cow --version

🦀 Cargo

# Crate is cow-cli, binary is cow
cargo install cow-cli

# Verify
cow --version

Requirements: macOS 10.13 High Sierra or later (clonefile(2) became stable in 10.13). Works on Apple Silicon and Intel — the Homebrew formula installs a universal binary. Linux and Windows are not supported; the CoW mechanism requires APFS.