nix-shell-direnv - SKILL.md Agent Skill

name: nix-shell-direnv description: Detect and use Nix shell environments via direnv when running commands. Use BEFORE running any shell command -- the skill checks for Nix indicators and adjusts execution accordingly, so it is safe to run even in projects without Nix. disable-model-invocation: true

Nix Shell / direnv Awareness

When running shell commands in a project, check for a Nix shell environment first.

Detection

Before executing commands, look for these indicators:

.envrc containing use nix, use flake, or nix-shell
shell.nix or default.nix in the project root
flake.nix with a devShells output

Behavior

If a Nix shell environment is detected:

Prefix commands with direnv exec . to ensure the environment is loaded
If direnv is unavailable, fall back to nix-shell --run "<command>" or nix develop -c <command>
Do not install packages globally via npm install -g, pip install, etc. -- the Nix shell provides them

Examples

# BAD -- runs outside the Nix environment
npm test

# GOOD -- uses direnv to load the Nix shell
direnv exec . npm test

# GOOD -- fallback without direnv
nix-shell --run "npm test"
nix develop -c npm test

Exceptions

Skip the prefix when the command is purely git, file I/O, or unrelated to the project's toolchain (e.g., git status, ls, mkdir).