flox-environments

flox-environments helps create reproducible, cross-platform (macOS/Linux) development environments with Flox, a declarative Nix-based environment manager. It solves "works on my machine" problems by defining an environment in a single TOML manifest so every developer, CI job, and fresh laptop gets identical packages, tools, and configuration — without containers or VMs, and with access to over 150,000 packages. It is the right tool when a project needs system-level packages (compilers, databases, native libs like openssl/BLAS) alongside language dependencies, when multiple tools must coexist, when reproducibility matters, or when AI agents need to install project-scoped tools without sudo or system pollution.

Environments are defined in .flox/env/manifest.toml and entered with flox activate. The skill documents essential commands (flox init, flox search, flox show, flox install, flox list, flox activate, flox activate -- <cmd>, flox edit) and the manifest sections [install], [vars], [hook] (on-activate scripts that run every activation), [profile] (interactive shell functions/aliases), and [options] (supported systems). It explains version pinning (nodejs.version = "^20.0", exact versions), platform-specific packages via .systems, conflict resolution with priority (lower wins), and grouping with pkg-group. Key Flox environment variables are covered: $FLOX_ENV (runtime path to installed packages), $FLOX_ENV_CACHE (persistent local storage that survives rebuilds), and $FLOX_ENV_PROJECT (project root). Language recipes are provided for Python with uv, Node.js, Rust, Go, and C/C++, along with hook/profile guidance and anti-patterns (avoid absolute paths, avoid exit in hooks).

It targets teams standardizing toolchains, developers onboarding with one command, and agent/vibe-coding setups needing sudo-free tools. The stated prerequisite is that Flox must be installed first (see flox.dev/docs for macOS, Linux, and Docker). The skill notes when Flox is not the best fit: a single language runtime with no system dependencies may only need standard tooling (nvm, pyenv, rustup), and full OS-level isolation may call for containers — Flox sits between them as declarative, reproducible environments without container overhead.