# Nix Justfile

> Conventions for writing justfile recipes in Nix-based projects.

- Skill: `juspay/nix-justfile` (Agent Skill)
- Install (CLI): `npx skillmds@latest add juspay/nix-justfile`
- Raw SKILL.md: https://api.skillmd.com/api/skills/juspay/nix-justfile/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: juspay (https://skillmd.com/u/juspay)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/juspay/nix-justfile

---


# Justfile in Nix projects

## Doc comments

Every recipe must have a doc comment (`#` line above the recipe name).

## Devshell detection

Use a `nix_shell` variable to auto-detect whether we're inside `nix develop`:

```just
nix_shell := if env('IN_NIX_SHELL', '') != '' { '' } else { 'nix develop -c' }
```

Prefix commands that need devshell tools (node, trunk, cargo-watch, etc.) with `{{nix_shell}}`. Recipes that invoke `nix` directly (build, run, flake commands) don't need it.

## Legibility

Long chained commands should use multiline `\` continuations.