Udderly instant pastures.

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 pasture and let them work in parallel.

How it works Docs GitHub

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

20 active pastures

23 MB total disk delta

saved vs. full clones

~158.7 GB npm / yarn

~119.3 GB pnpm / bun

the developer's own experience — 18 pastures across several JS monorepos. your mileage will vary.

the alternatives

Every other approach is udderly wrong.

Running multiple AI coding agents in parallel means multiple isolated pastures. 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 pasture. 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 pastures. Reads .cow.json for project-specific cleanup rules and post-clone commands.

Point your agent at it

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

cli reference

Eighteen commands. One binary.

No daemons to manage, no subscriptions, no install step in your pastures.

# create a named pasture; --branch overrides the branch name $ cow create feat-auth --source ~/my-project --branch feat/auth Cloning /Users/joe/my-project ... 🐄 Created pasture 'feat-auth' at ~/.cow/pastures/feat-auth # omit the name and cow auto-generates agent-1, agent-2, … $ cow create --source ~/my-project Cloning /Users/joe/my-project ... 🐄 Created pasture 'agent-1' at ~/.cow/pastures/agent-1

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

# prompts when pasture has uncommitted changes $ cow remove agent-2 ⚠ Pasture 'agent-2' has uncommitted changes: M src/api/routes.rs Remove anyway? Changes will be lost. [y/N]: y 🐄 Removed pasture 'agent-2' # --force skips the prompt $ cow remove --force agent-1 feat-auth 🐄 Removed pasture 'agent-1' 🐄 Removed pasture 'feat-auth'

# write a patch file $ cow extract agent-2 --patch ~/auth-changes.patch Patch written to /Users/joe/auth-changes.patch # land the branch in the source repo so you can push a PR $ cow extract agent-2 --branch feat/auth-review Branch 'feat/auth-review' created in source repo at ~/my-project # clean up $ cow remove --force agent-2 🐄 Removed pasture 'agent-2'

$ cow status agent-2 🐄 Pasture: agent-2 Source: /Users/joe/my-project Branch: feat/api VCS: git Status: dirty Created: 2026-03-03 09:52:00 UTC Disk delta: 14 KB (estimated from modified file sizes) Modified files: M src/api/routes.rs A src/api/middleware.rs

# discover git worktrees, jj workspaces, and orphaned cow dirs $ cow migrate --source ~/my-project Found 2 candidate(s) to migrate: feat-auth — /Users/joe/my-project-feat-auth feat-api — /Users/joe/my-project-feat-api Run with --all to migrate all of them. # preview what would happen without making any changes $ cow migrate --source ~/my-project --all --dry-run [dry-run] Would migrate 'feat-auth' (/Users/joe/my-project-feat-auth) [dry-run] Would migrate 'feat-api' (/Users/joe/my-project-feat-api) # migrate all candidates (skips dirty pastures) $ cow migrate --source ~/my-project --all Skipping 'feat-api' — has uncommitted changes (use --force to override). Migrated 'feat-auth' # migrate everything, including dirty pastures $ cow migrate --source ~/my-project --all --force Migrated 'feat-api'

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)	~130ms	~1s (no modules)	3–8 minutes
Extra disk per pasture	~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 pasture management as MCP tools. Your AI orchestrator can create and tear down pastures without shelling out.

Add to Claude Code

Drop this snippet into your ~/.claude.json or a project-local .mcp.json to let Claude manage its own pastures 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.json
{
  "mcpServers": {
    "cow": {
      "command": "cow",
      "args": ["mcp"]
    }
  }
}

menubar companion

Meet Herd. 🐄

A native macOS menubar app that gives you a live view of all your pastures — no terminal needed.

Everything at a glance

Pastures are grouped by project. Hover any row to reveal quick actions: open in Finder, open in Terminal, sync from source, or remove with a confirmation prompt.

A stats strip at the bottom shows real-time disk savings versus a traditional clone.

Herd calls the cow CLI under the hood — it requires cow to be installed.

# Install Herd via Homebrew
brew install joeinnes/tap/cow-herd

# Copy to Applications
cp -r $(brew --prefix)/opt/cow-herd/Herd.app \
  /Applications/

# First launch: right-click → Open
# to bypass Gatekeeper (unsigned app)

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.