Flox Environments

Flox Environments (Slim)

Flox provides reproducible development environments defined in a manifest.toml that gets committed to git. When a contributor runs flox activate, they get every dependency automatically — on any Linux or macOS machine.

Core Commands

flox init                       # Create new environment
flox search <string> [--all]    # Find packages
flox show <pkg>                 # Show available versions
flox install <pkg>              # Add package
flox list                       # List installed packages
flox activate                   # Enter environment
flox activate -- <cmd>          # Run single command

Key Paths

• .flox/env/manifest.toml — Environment definition
• .flox/env.json — Environment metadata
• $FLOX_ENV_CACHE — Persistent local storage
• $FLOX_ENV_PROJECT — Project root (where .flox/ lives)
• $FLOX_ENV — Path to environment's usr tree

Manifest Structure

[install]
ripgrep.pkg-path = "ripgrep"
nodejs.pkg-path = "nodejs"
nodejs.version = "^20.0"

[vars]
MY_VAR = "value"

[hook]
on-activate = """
  # Runs every activation (keep fast and idempotent)
"""

[profile.common]
# Shell functions and aliases available to users

[options]
systems = [
  "aarch64-darwin",
  "aarch64-linux",
  "x86_64-darwin",
  "x86_64-linux",
]

Package Installation

[install]
# Simple package
ripgrep.pkg-path = "ripgrep"

# Nested package path
pip.pkg-path = "python312Packages.pip"

# Version-pinned
nodejs.pkg-path = "nodejs"
nodejs.version = "^20.0"

# Platform-specific
valgrind.pkg-path = "valgrind"
valgrind.systems = ["x86_64-linux", "aarch64-linux"]

# Conflict resolution (lower = higher priority)
gcc.pkg-path = "gcc"
gcc.priority = 3

Language Detection Patterns

When creating an environment for an existing project, detect the language stack and install appropriate packages.

Python (pyproject.toml, setup.py, requirements.txt)

[install]
python.pkg-path = "python312"
uv.pkg-path = "uv"

Hook pattern for venv:

[hook]
on-activate = """
  venv="$FLOX_ENV_CACHE/venv"
  if [ ! -d "$venv" ]; then
    uv venv "$venv" --python python3 --quiet
  fi
  if [ -f "$venv/bin/activate" ]; then
    source "$venv/bin/activate"
  fi
"""

Node.js (package.json)

[install]
nodejs.pkg-path = "nodejs"
nodejs.version = "^20.0"
# Add yarn or pnpm if lockfile found

Rust (Cargo.toml)

[install]
rustup.pkg-path = "rustup"
# Or for pinned toolchain:
rust-toolchain.pkg-path = "rust-bin.stable.latest.default"

Go (go.mod)

[install]
go.pkg-path = "go"

C/C++ (CMakeLists.txt, Makefile)

[install]
gcc.pkg-path = "gcc"
cmake.pkg-path = "cmake"
gnumake.pkg-path = "gnumake"
# For C++ stdlib headers:
gcc-unwrapped.pkg-path = "gcc-unwrapped"

Common Tools to Include

These are often useful regardless of language:

[install]
git.pkg-path = "git"
jq.pkg-path = "jq"
curl.pkg-path = "curl"

Best Practices

• Never use absolute paths in hooks — use $FLOX_ENV, $FLOX_ENV_PROJECT, $FLOX_ENV_CACHE
• Use return not exit in hooks
• Keep hooks fast and idempotent
• Cache downloads in $FLOX_ENV_CACHE
• Check manifest before installing new packages
• Use flox search --all for broader results (search is case-sensitive)

Troubleshooting

• Package conflicts: Use different pkg-group values or adjust priority
• Manifest syntax errors: Prevent all flox commands from working — fix the TOML first
• Need libstdc++: Install gcc-unwrapped, not gcc

For More

The full Flox plugin (claude plugin install flox) provides additional skills:

• flox-services — Background processes and databases
• flox-builds — Reproducible package builds
• flox-containers — Docker/OCI image creation
• flox-cuda — GPU/CUDA development
• flox-sharing — Environment composition and layering
• flox-publish — Package distribution