How do I install the Writing Nix Config skill?

Run npx skillmds@latest add joshsymonds/writing-nix-config in your terminal (requires Node.js), paste this page's agent-chat prompt into Claude, Cursor, or any MCP-connected agent, or download the SKILL.md file and copy it into your agent's skills directory.

Is Writing Nix Config safe to use?

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Which AI agents work with Writing Nix Config?

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Is Writing Nix Config free to use?

Yes. Installing skills from SkillMD is free, and the skill stays under its author's original license.

Who published Writing Nix Config?

joshsymonds (@joshsymonds) published this skill. Their other Agent Skills are listed on their SkillMD profile.

Writing Nix Config by joshsymonds — Agent Skill

Name: Writing Nix Config
Author: joshsymonds

File contents

Nix Configuration Patterns

Critical Rules

Rule	Why
Run `update` after changes	Nothing takes effect until rebuilt
Run `git add` before `nix flake check`	Flakes only see git-tracked files
Use `lib.fakeHash` for unknown hashes	Nix will tell you the real hash on build failure

Common Mistakes

Wrong	Right
Running `nix flake check` on new files without `git add`	`git add <file>` first
Editing config and expecting immediate effect	Run `update` to rebuild
Guessing SHA256 hashes	Use `lib.fakeHash`, build, copy real hash from error
Adding package only to overlay	Also add to `pkgs/default.nix`

Commands

update                              # Rebuild current system
nix flake check                     # Validate flake
nix build .#<package>               # Build package
nix eval .#nixosConfigurations.<host>.config.<option>  # Check config value

Package Pattern

# pkgs/<name>/default.nix
{ lib, stdenv, fetchFromGitHub, ... }:
stdenv.mkDerivation rec {
  pname = "name";
  version = "1.0.0";

  src = fetchFromGitHub {
    owner = "...";
    repo = "...";
    rev = "v${version}";
    hash = "sha256-AAAA...";  # Use lib.fakeHash first, nix will tell you real hash
  };

  meta = with lib; {
    description = "...";
    license = licenses.mit;
    platforms = platforms.all;
  };
}

Then add to pkgs/default.nix and overlays/default.nix.

Home Manager Module Pattern

# home-manager/<app>/default.nix
{ pkgs, lib, ... }: {
  home.packages = [ pkgs.app ];

  # Or use programs.<app> if module exists
  programs.app = {
    enable = true;
    settings = { ... };
  };
}

Then import in home-manager/common.nix or platform-specific file.

Agenix Secret Pattern

# 1. Add to secrets/secrets.nix
"secrets/hosts/<host>/<name>.age".publicKeys = keys.<host>;

# 2. Declare in host config
age.secrets."<name>" = {
  file = ../../secrets/hosts/<host>/<name>.age;
  owner = "<service-user>";
  mode = "0400";
};

# 3. Create the secret
agenix -e secrets/hosts/<host>/<name>.age

This Repo's Systems

Host	Platform	Notes
ninuan	macOS	Primary dev, Aerospace WM
ultraviolet	NixOS	Headless server
bluedesert	NixOS	Headless server
echelon	NixOS	Headless server

---name: writing-nix-configdescription: Patterns for this nix-config flake repository. Use when editing .nix files, adding packages, creating modules, or debugging flake issues.---# Nix Configuration Patterns## Critical Rules| Rule | Why ||------|-----|| Run `update` after changes | Nothing takes effect until rebuilt || Run `git add` before `nix flake check` | Flakes only see git-tracked files || Use `lib.fakeHash` for unknown hashes | Nix will tell you the real hash on build failure |## Common Mistakes| Wrong | Right ||-------|-------|| Running `nix flake check` on new files without `git add` | `git add <file>` first || Editing config and expecting immediate effect | Run `update` to rebuild || Guessing SHA256 hashes | Use `lib.fakeHash`, build, copy real hash from error || Adding package only to overlay | Also add to `pkgs/default.nix` |## Commands```bashupdate # Rebuild current systemnix flake check # Validate flakenix build .#<package> # Build packagenix eval .#nixosConfigurations.<host>.config.<option> # Check config value```## Package Pattern```nix# pkgs/<name>/default.nix{ lib, stdenv, fetchFromGitHub, ... }:stdenv.mkDerivation rec { pname = "name"; version = "1.0.0"; src = fetchFromGitHub { owner = "..."; repo = "..."; rev = "v${version}"; hash = "sha256-AAAA..."; # Use lib.fakeHash first, nix will tell you real hash }; meta = with lib; { description = "..."; license = licenses.mit; platforms = platforms.all; };}```Then add to `pkgs/default.nix` and `overlays/default.nix`.## Home Manager Module Pattern```nix# home-manager/<app>/default.nix{ pkgs, lib, ... }: { home.packages = [ pkgs.app ]; # Or use programs.<app> if module exists programs.app = { enable = true; settings = { ... }; };}```Then import in `home-manager/common.nix` or platform-specific file.## Agenix Secret Pattern```nix# 1. Add to secrets/secrets.nix"secrets/hosts/<host>/<name>.age".publicKeys = keys.<host>;# 2. Declare in host configage.secrets."<name>" = { file = ../../secrets/hosts/<host>/<name>.age; owner = "<service-user>"; mode = "0400";};# 3. Create the secretagenix -e secrets/hosts/<host>/<name>.age```## This Repo's Systems| Host | Platform | Notes ||------|----------|-------|| ninuan | macOS | Primary dev, Aerospace WM || ultraviolet | NixOS | Headless server || bluedesert | NixOS | Headless server || echelon | NixOS | Headless server |

Frequently asked questions

Writing Nix Config