| name | nix |
| description | Use for ALL Nix flake configuration questions. This includes file structure (flake.nix, nix/, .envrc), adding/removing packages or binaries, PATH configuration, development shells, pre-commit hooks, formatters, linters, enforcers, environment variables, adding registries, and how the Nix template structure works. Use when user asks about nix, flake, packages, binaries, shells, PATH, formatting, linting, git hooks, or registries. |
Nix Flake Configuration Skill
When to Use
User asks about nix files, packages, binaries, PATH, shells, formatters, linters, hooks, registries, or .envrc.
Instructions
Step 1: Read the Actual Files First
Always read flake.nix and the target nix file before making changes. Registry names, variable names, environment groups, and shells are project-specific.
Step 2: Consult the Docs
Full guide: nix.md
Step 3: Quick Reference
| Task | Files to Edit | Apply With |
|---|
| Add package | packages.nix, env.nix | direnv reload |
| Add env group | env.nix, then use in shells.nix | direnv reload |
| Add shell | shells.nix (only change buildInputs, always inherit shellHook) | nix develop .#name |
| Add formatter | fmt.nix | direnv reload |
| Add hook | pre-commit.nix (prefix a-) | direnv reload |
| Add binary to PATH | packages.nix → env.nix (nix); or .envrc PATH_add (repo-declared non-nix paths) | direnv reload |
| Add registry | flake.nix, packages.nix | nix flake update |
Step 4: Critical Rules
- Read
flake.nix first — it defines all variable names and wiring
shellHook must be inherited — all shells use inherit shellHook;, never override or customize it (breaks downstream nix-resolvers)- Prefix custom hooks with
a- — e.g., a-eslint, a-file-size
- PATH is managed by nix — add packages via
packages.nix → env.nix. .envrc PATH_add is only for paths whose existence is declared by a repo config file (e.g., node_modules/.bin from package.json, ~/.dotnet/tools from .config/dotnet-tools.json)
nix flake update only for new registries — all other changes just need direnv reload.envrc is minimal — only watch_file, use flake, and repo-declared PATH_add. No env var exports, no arbitrary external paths
Step 5: Patterns and Examples
See reference.md for file patterns and code examples.
