name: devenv version: 1.0 description: Devenv Skill

Devenv Skill

A specialized skill for creating fast, declarative, reproducible development environments using devenv.sh and Nix.

Skill Overview

Purpose: Provide comprehensive support for devenv configuration, environment setup, language configuration, service management, and development workflow automation.

Invoke When:

Creating new development environments
Configuring language tooling and dependencies
Setting up development services (databases, caches, queues)
Managing development processes and scripts
Configuring pre-commit hooks
Setting up containerized development
Troubleshooting devenv issues
Migrating from docker-compose or other dev tools

Core Capabilities

1. Installation & Setup

Prerequisites

# Install Nix first (if not already installed)
curl -L https://nixos.org/nix/install | sh

# Or on NixOS - already installed

Install devenv

# Using nix-env
nix-env --install --attr devenv -f https://github.com/NixOS/nixpkgs/tarball/nixpkgs-unstable

# Using nix profile (recommended)
nix profile install nixpkgs#devenv

# Verify installation
devenv version

On NixOS/home-manager

# NixOS configuration.nix
environment.systemPackages = with pkgs; [
  devenv
];

# Or home-manager
home.packages = with pkgs; [
  devenv
];

Optional: Cachix for faster builds

# Install cachix
nix-env -iA cachix -f https://cachix.org/api/v1/install

# Use devenv cache
cachix use devenv

2. Project Initialization

Initialize New Project

# Create project directory
mkdir my-project && cd my-project

# Initialize devenv
devenv init

# This creates:
# - devenv.nix (main configuration)
# - devenv.yaml (inputs/composition)
# - .envrc (direnv integration)
# - .gitignore (devenv-specific ignores)

Generated Files

devenv.nix - Main configuration:

{ pkgs, lib, config, ... }:

{
  # Package list
  packages = [ pkgs.git ];

  # Language configuration
  languages.python = {
    enable = true;
    version = "3.11";
  };

  # Services
  services.postgres.enable = true;

  # Processes
  processes.app.exec = "python manage.py runserver";

  # Environment variables
  env.DATABASE_URL = "postgresql://localhost/mydb";

  # Scripts
  scripts.hello.exec = "echo Hello from devenv!";

  # Pre-commit hooks
  pre-commit.hooks = {
    nixfmt.enable = true;
  };
}

devenv.yaml - Inputs configuration:

inputs:
  nixpkgs:
    url: github:NixOS/nixpkgs/nixpkgs-unstable

# Optional: Import other devenv configs
imports:
  - path: ../shared-config
    inputs: {}

.envrc - Direnv integration:

if ! has nix_direnv_version || ! nix_direnv_version 3.0.4; then
  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.4/direnvrc" "sha256-DzlYZ33mWF/Gs8DDeyjr8mnVmQGx7ASYqA5WlxwvBG4="
fi

use devenv

3. Core Commands

Essential Commands

# Enter development shell
devenv shell

# Run tests
devenv test

# Start all processes/services
devenv up

# Start in background
devenv up -d

# Search for packages
devenv search <package-name>

# Update inputs (like nix flake update)
devenv update

# Garbage collect old environments
devenv gc

# Print environment info
devenv info

# Show container configuration
devenv container

Using with direnv

# Allow direnv (first time)
direnv allow

# Auto-enter shell when cd'ing to directory
cd my-project  # Automatically activates devenv

4. Language Configuration

55+ Languages Supported

Python

languages.python = {
  enable = true;
  version = "3.11.3";  # Specific version

  # Virtual environment
  venv.enable = true;
  venv.requirements = ./requirements.txt;

  # Poetry support
  poetry.enable = true;
  poetry.activate.enable = true;
  poetry.install.enable = true;
};

# Add Python packages
packages = with pkgs; [
  python311Packages.black
  python311Packages.pytest
  python311Packages.mypy
];

JavaScript/Node.js

languages.javascript = {
  enable = true;
  package = pkgs.nodejs_20;

  # NPM support
  npm.enable = true;
  npm.install.enable = true;

  # Yarn support
  yarn.enable = true;
  yarn.install.enable = true;

  # PNPM support
  pnpm.enable = true;
  pnpm.install.enable = true;
};

# Or use bun
languages.javascript = {
  enable = true;
  bun.enable = true;
};

TypeScript

languages.typescript = {
  enable = true;
};

packages = with pkgs; [
  nodePackages.typescript
  nodePackages.typescript-language-server
];

Rust

languages.rust = {
  enable = true;
  channel = "stable";  # or "nightly", "beta"

  # Components
  components = [ "rustc" "cargo" "clippy" "rustfmt" ];

  # Targets
  targets = [ "wasm32-unknown-unknown" ];
};

Go

languages.go = {
  enable = true;
  package = pkgs.go_1_21;
};

env.GOPATH = "${config.env.DEVENV_ROOT}/.go";
env.GOBIN = "${config.env.DEVENV_ROOT}/.go/bin";

Ruby

languages.ruby = {
  enable = true;
  version = "3.2.2";

  # Bundler support
  bundler.enable = true;
};

PHP

languages.php = {
  enable = true;
  version = "8.2";

  # Extensions
  extensions = [ "mysqli" "pdo" "pdo_mysql" ];

  # Composer
  fpm.pools.web = {
    settings = {
      "pm" = "dynamic";
      "pm.max_children" = 5;
    };
  };
};

# Composer packages
packages = [ pkgs.php82Packages.composer ];

Java

languages.java = {
  enable = true;
  jdk.package = pkgs.jdk17;

  # Gradle
  gradle.enable = true;

  # Maven
  maven.enable = true;
};

Elixir

languages.elixir = {
  enable = true;
  package = pkgs.elixir_1_15;
};

# With Erlang version
languages.erlang = {
  enable = true;
  package = pkgs.erlang_26;
};

Haskell

languages.haskell = {
  enable = true;
  package = pkgs.ghc94;

  # Stack support
  stack.enable = true;
};

Terraform/OpenTofu

languages.terraform = {
  enable = true;
};

# Or OpenTofu (Terraform fork)
languages.opentofu = {
  enable = true;
};

Nix

languages.nix = {
  enable = true;
};

packages = with pkgs; [
  nixd  # Nix LSP
  nixfmt  # Formatter
  statix  # Linter
];

5. Services Configuration

30+ Pre-configured Services

PostgreSQL

services.postgres = {
  enable = true;
  package = pkgs.postgresql_15;

  # Initial databases
  initialDatabases = [
    { name = "myapp_dev"; }
    { name = "myapp_test"; }
  ];

  # Initial SQL script
  initialScript = ''
    CREATE USER myapp WITH PASSWORD 'dev';
    GRANT ALL PRIVILEGES ON DATABASE myapp_dev TO myapp;
  '';

  # Listen address
  listen_addresses = "127.0.0.1";

  # Port
  port = 5432;

  # Extensions
  extensions = extensions: [
    extensions.postgis
    extensions.pg_cron
  ];

  # Settings
  settings = {
    max_connections = 100;
    shared_buffers = "128MB";
  };
};

# Access via:
env.DATABASE_URL = "postgresql://localhost:5432/myapp_dev";

MySQL

services.mysql = {
  enable = true;
  package = pkgs.mysql80;

  # Initial databases
  initialDatabases = [
    { name = "myapp"; }
  ];

  # Settings
  settings = {
    mysqld = {
      port = 3306;
      bind_address = "127.0.0.1";
    };
  };
};

env.DATABASE_URL = "mysql://root@localhost:3306/myapp";

Redis

services.redis = {
  enable = true;
  port = 6379;

  # Bind address
  bind = "127.0.0.1";
};

env.REDIS_URL = "redis://localhost:6379";

MongoDB

services.mongodb = {
  enable = true;

  # Additional config
  additionalConfig = ''
    net:
      port: 27017
      bindIp: 127.0.0.1
  '';
};

Elasticsearch

services.elasticsearch = {
  enable = true;
  package = pkgs.elasticsearch7;

  # Cluster name
  cluster_name = "devenv";

  # Port
  port = 9200;
};

RabbitMQ

services.rabbitmq = {
  enable = true;

  # Management plugin
  managementPlugin.enable = true;
  managementPlugin.port = 15672;
};

env.RABBITMQ_URL = "amqp://localhost:5672";

Kafka

services.kafka = {
  enable = true;
  port = 9092;

  # Zookeeper (required)
  zookeeper.enable = true;
};

Nginx

services.nginx = {
  enable = true;

  httpConfig = ''
    server {
      listen 8080;
      server_name localhost;

      location / {
        proxy_pass http://localhost:3000;
        proxy_set_header Host $host;
      }
    }
  '';
};

Caddy

services.caddy = {
  enable = true;

  config = ''
    :8080 {
      reverse_proxy localhost:3000
    }
  '';
};

MinIO (S3-compatible storage)

services.minio = {
  enable = true;

  # Credentials
  accessKey = "minioadmin";
  secretKey = "minioadmin";

  # Buckets
  buckets = [ "my-bucket" ];
};

env.AWS_ENDPOINT = "http://localhost:9000";
env.AWS_ACCESS_KEY_ID = "minioadmin";
env.AWS_SECRET_ACCESS_KEY = "minioadmin";

Mailhog (Email testing)

services.mailhog = {
  enable = true;

  # SMTP port
  smtpPort = 1025;

  # Web UI port
  uiPort = 8025;
};

env.SMTP_HOST = "localhost";
env.SMTP_PORT = "1025";

Vault (Secrets management)

services.vault = {
  enable = true;

  # Address
  address = "127.0.0.1:8200";
};

6. Process Management

Define Processes

# Simple processes
processes = {
  # Web server
  web.exec = "python manage.py runserver 0.0.0.0:8000";

  # Worker
  worker.exec = "celery -A myapp worker -l info";

  # Frontend dev server
  frontend.exec = "cd frontend && npm run dev";

  # Background task
  scheduler.exec = "python manage.py scheduler";
};

Advanced Process Configuration

processes = {
  api = {
    exec = "python -m uvicorn main:app --reload";

    # Process-specific environment
    process-compose = {
      environment = {
        PORT = "8000";
        LOG_LEVEL = "debug";
      };

      # Working directory
      working_dir = "${config.env.DEVENV_ROOT}/backend";

      # Availability check
      availability = {
        restart = "on_failure";
        max_restarts = 3;
      };

      # Readiness probe
      readiness_probe = {
        http_get = {
          host = "localhost";
          port = 8000;
          path = "/health";
        };
        initial_delay_seconds = 2;
        period_seconds = 10;
      };

      # Dependencies
      depends_on.db.condition = "process_healthy";
    };
  };

  db = {
    exec = "postgres";
    process-compose = {
      readiness_probe = {
        exec.command = "pg_isready -h localhost";
      };
    };
  };
};

Start Processes

# Start all processes with TUI
devenv up

# Start in background
devenv up -d

# Watch logs
tail -f .devenv/state/process-compose/*.log

# Stop processes
# Ctrl+C (if in foreground)
# or kill the background process

7. Scripts & Tasks

Define Scripts

scripts = {
  # Simple script
  hello.exec = ''
    echo "Hello from devenv!"
  '';

  # Database setup
  db-setup.exec = ''
    echo "Setting up database..."
    psql -h localhost -U postgres -d myapp_dev -f schema.sql
    echo "Database ready!"
  '';

  # Run tests
  test.exec = ''
    pytest tests/ -v
  '';

  # Build project
  build.exec = ''
    echo "Building project..."
    npm run build
    echo "Build complete!"
  '';

  # Migration
  migrate.exec = ''
    python manage.py migrate
  '';

  # Seed data
  seed.exec = ''
    python manage.py loaddata fixtures/*.json
  '';
};

Use Scripts

# Inside devenv shell
hello
db-setup
test
build
migrate
seed

Tasks (Entertest/Entersh hooks)

# Run on shell entry
enterShell = ''
  echo "Welcome to the development environment!"
  echo "Database: $DATABASE_URL"
  echo "Redis: $REDIS_URL"
  echo ""
  echo "Available commands:"
  echo "  - db-setup: Initialize database"
  echo "  - test: Run test suite"
  echo "  - migrate: Run migrations"
'';

# Run on test
enterTest = ''
  echo "Running tests..."
  pytest tests/
  echo "Running linters..."
  flake8 src/
'';

8. Environment Variables

Configuration

# Simple variables
env = {
  DATABASE_URL = "postgresql://localhost:5432/myapp";
  REDIS_URL = "redis://localhost:6379";

  # API keys (for development only!)
  API_KEY = "dev-key-12345";

  # Application config
  DEBUG = "true";
  LOG_LEVEL = "debug";

  # Paths
  DATA_DIR = "${config.env.DEVENV_ROOT}/data";
  UPLOAD_DIR = "${config.env.DEVENV_ROOT}/uploads";
};

# Dynamic variables
env.GIT_ROOT = config.git.root;
env.DEVENV_STATE = config.devenv.state;

Dotenv Support

# Load from .env file
dotenv.enable = true;
dotenv.filename = ".env.local";

# Or disallow .env files (force explicit config)
dotenv.disableHint = true;

Secret Management

# Use sops-nix or similar for real secrets
# Never commit secrets to devenv.nix

# Example with sops
imports = [ inputs.sops-nix.nixosModules.sops ];

sops = {
  defaultSopsFile = ./secrets.yaml;
  secrets.api_key = {
    path = "${config.env.DEVENV_ROOT}/.secrets/api_key";
  };
};

# Reference in environment
env.API_KEY = "$(cat ${config.env.DEVENV_ROOT}/.secrets/api_key)";

9. Pre-commit Hooks

Common Hooks

pre-commit.hooks = {
  # Nix formatting
  nixfmt.enable = true;

  # Nix linting
  statix.enable = true;

  # Python
  black.enable = true;
  isort.enable = true;
  flake8.enable = true;
  mypy.enable = true;
  pylint.enable = true;

  # JavaScript/TypeScript
  prettier.enable = true;
  eslint.enable = true;

  # Shell
  shellcheck.enable = true;
  shfmt.enable = true;

  # YAML
  yamllint.enable = true;

  # Markdown
  markdownlint.enable = true;

  # Trailing whitespace
  trailing-whitespace.enable = true;

  # File size check
  check-added-large-files.enable = true;

  # Merge conflict check
  check-merge-conflicts.enable = true;
};

Custom Hooks

pre-commit.hooks = {
  custom-check = {
    enable = true;
    name = "Custom Check";
    entry = "${pkgs.python3}/bin/python scripts/check.py";
    files = "\\.py$";
    pass_filenames = true;
  };

  license-header = {
    enable = true;
    name = "License Header Check";
    entry = "${pkgs.bash}/bin/bash scripts/check-license.sh";
    files = "\\.(py|js|ts)$";
  };
};

Install Hooks

# Inside devenv shell
git init  # if not already initialized
devenv shell  # Hooks auto-install on shell entry

10. Containers & Deployment

Generate Container Image

# Enable container support
containers.myapp.name = "myapp";
containers.myapp.registry = "docker.io/myuser";

# Startup command
containers.myapp.startupCommand = pkgs.writeScript "start" ''
  #!${pkgs.bash}/bin/bash
  python manage.py runserver 0.0.0.0:8000
'';

# Copy files
containers.myapp.copyToRoot = [
  (pkgs.buildEnv {
    name = "myapp-root";
    paths = [ ./app ./requirements.txt ];
  })
];

Build Container

# Generate container
devenv container myapp

# Outputs container tarball
# Load into Docker:
docker load < myapp.tar.gz
docker run -p 8000:8000 myapp

11. Packages & Dependencies

System Packages

packages = with pkgs; [
  # Development tools
  git
  gh  # GitHub CLI
  jq
  yq

  # Database clients
  postgresql
  redis

  # HTTP tools
  curl
  httpie

  # Monitoring
  htop
  bottom

  # Editors (if not using system)
  vim
  neovim

  # Debugging
  gdb
  lldb

  # Build tools
  cmake
  gnumake

  # Documentation
  pandoc
];

Language-specific packages

# Python
packages = with pkgs.python311Packages; [
  requests
  flask
  django
  pytest
  black
];

# Node.js
packages = with pkgs.nodePackages; [
  typescript
  typescript-language-server
  prettier
  eslint
];

12. Composition & Imports

Shared Configuration

# shared/common.nix
{ pkgs, ... }:
{
  packages = with pkgs; [
    git
    jq
    curl
  ];

  languages.nix.enable = true;

  pre-commit.hooks.nixfmt.enable = true;
}

Import in Project

# devenv.nix
{ pkgs, inputs, ... }:
{
  imports = [
    ./shared/common.nix
  ];

  # Project-specific config
  languages.python.enable = true;
  services.postgres.enable = true;
}

Using devenv.yaml

# devenv.yaml
inputs:
  nixpkgs:
    url: github:NixOS/nixpkgs/nixpkgs-unstable

  # Import shared devenv config
  shared:
    url: path:../shared-devenv

# Use shared modules
imports:
  - path: shared
    inputs: {}

13. Testing Integration

devenv test

# Define tests
enterTest = ''
  echo "Running test suite..."

  # Unit tests
  pytest tests/unit -v

  # Integration tests
  pytest tests/integration -v

  # Linting
  flake8 src/
  black --check src/

  # Type checking
  mypy src/

  echo "All tests passed!"
'';

Run Tests

# Run all tests
devenv test

# In CI
nix develop --command devenv test

CI Integration

# .github/workflows/test.yml
name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: cachix/install-nix-action@v22
      - uses: cachix/cachix-action@v12
        with:
          name: devenv
      - run: nix profile install nixpkgs#devenv
      - run: devenv test

Common Patterns

Pattern 1: Full-Stack Web Application

{ pkgs, ... }:
{
  # Frontend
  languages.javascript = {
    enable = true;
    npm.enable = true;
  };

  # Backend
  languages.python = {
    enable = true;
    venv.enable = true;
  };

  # Database
  services.postgres.enable = true;
  services.redis.enable = true;

  # Processes
  processes = {
    frontend.exec = "cd frontend && npm run dev";
    backend.exec = "python manage.py runserver";
    worker.exec = "celery -A app worker";
  };

  # Environment
  env = {
    DATABASE_URL = "postgresql://localhost/myapp";
    REDIS_URL = "redis://localhost:6379";
  };

  # Scripts
  scripts = {
    setup.exec = ''
      npm install --prefix frontend
      pip install -r requirements.txt
      python manage.py migrate
    '';

    test.exec = ''
      pytest backend/tests
      npm run test --prefix frontend
    '';
  };
}

Pattern 2: Microservices Development

{ pkgs, ... }:
{
  # Multiple languages
  languages.go.enable = true;
  languages.rust.enable = true;
  languages.javascript.enable = true;

  # Shared services
  services.postgres.enable = true;
  services.redis.enable = true;
  services.kafka.enable = true;

  # All services as processes
  processes = {
    user-service.exec = "cd services/user && go run main.go";
    auth-service.exec = "cd services/auth && cargo run";
    api-gateway.exec = "cd gateway && npm start";
  };

  # Shared tools
  packages = with pkgs; [
    protobuf
    grpcurl
    kubectl
  ];
}

Pattern 3: Data Science Environment

{ pkgs, ... }:
{
  languages.python = {
    enable = true;
    version = "3.11";
  };

  # Data science packages
  packages = with pkgs.python311Packages; [
    numpy
    pandas
    matplotlib
    scikit-learn
    jupyter
    ipython
  ];

  # Services
  services.postgres.enable = true;
  services.mongodb.enable = true;

  # Jupyter notebook
  processes.jupyter.exec = "jupyter notebook --ip=0.0.0.0";

  # Scripts
  scripts = {
    notebook.exec = "jupyter notebook";
    lab.exec = "jupyter lab";
  };
}

Pattern 4: Mobile Development (React Native)

{ pkgs, ... }:
{
  languages.javascript = {
    enable = true;
    npm.enable = true;
  };

  packages = with pkgs; [
    nodejs
    watchman

    # Android
    android-tools
    androidStudioPackages.stable

    # iOS (macOS only)
    # cocoapods
  ];

  # Metro bundler
  processes.metro.exec = "npx react-native start";

  # Environment
  env = {
    ANDROID_HOME = "${pkgs.android-tools}/sdk";
  };

  scripts = {
    android.exec = "npx react-native run-android";
    ios.exec = "npx react-native run-ios";
  };
}

Pattern 5: DevOps/Infrastructure

{ pkgs, ... }:
{
  languages.terraform.enable = true;

  packages = with pkgs; [
    kubectl
    kubernetes-helm
    terraform
    ansible
    docker
    docker-compose

    # Cloud CLIs
    awscli2
    google-cloud-sdk
    azure-cli
  ];

  scripts = {
    k8s-dev.exec = "kubectl config use-context dev";
    k8s-prod.exec = "kubectl config use-context prod";

    deploy-dev.exec = ''
      terraform workspace select dev
      terraform apply -auto-approve
    '';
  };
}

Best Practices

DO ✅

Use devenv.yaml for input management

inputs:
  nixpkgs:
    url: github:NixOS/nixpkgs/nixpkgs-unstable

Pin dependencies with devenv.lock

# Commit devenv.lock to version control
git add devenv.lock

Use services instead of manual processes

# ✅ Good - use service
services.postgres.enable = true;

# ❌ Bad - manual process
processes.postgres.exec = "postgres -D ./data";

Leverage pre-commit hooks

pre-commit.hooks.nixfmt.enable = true;
pre-commit.hooks.black.enable = true;

Use enterShell for welcome messages

enterShell = ''
  echo "Development environment ready!"
  echo "Run 'devenv up' to start services"
'';

Define scripts for common tasks

scripts.setup.exec = ''
  # First-time setup
'';

Use composition for shared config
```
imports = [ ./shared/common.nix ];
```
Set up CI with devenv test
```
enterTest = ''
  pytest tests/
'';
```

Use environment-specific configs

env.DEBUG = "true";  # Development
# Override in production

Document your environment

# Add comments explaining decisions
services.postgres = {
  enable = true;
  # Using PostgreSQL 15 for JSON features
  package = pkgs.postgresql_15;
};

DON'T ❌

Don't commit secrets to devenv.nix

# ❌ Never do this
env.API_KEY = "secret-key-12345";

# ✅ Use dotenv or sops
dotenv.enable = true;

Don't use global nix-env installations

# ❌ Don't install globally
nix-env -iA nixpkgs.nodejs

# ✅ Use devenv packages
packages = [ pkgs.nodejs ];

Don't ignore devenv.lock

# ✅ Commit lock file
git add devenv.lock

Don't hardcode paths

# ❌ Bad
env.DATA_DIR = "/Users/me/projects/app/data";

# ✅ Good
env.DATA_DIR = "${config.env.DEVENV_ROOT}/data";

Don't skip direnv integration

# ✅ Use direnv for auto-activation
direnv allow

Don't mix package managers

# ❌ Don't use npm install globally
npm install -g typescript

# ✅ Use devenv packages
packages = [ pkgs.nodePackages.typescript ];

Don't ignore enterTest

# ✅ Always define tests
enterTest = "pytest tests/";

Troubleshooting

Issue 1: "command not found" in devenv shell

Solution:

# Ensure you're in the shell
devenv shell

# Or use direnv
direnv allow
cd .  # Re-enter directory

Issue 2: Service won't start

Solution:

# Check service state directory
ls -la .devenv/state/

# Remove service data and restart
rm -rf .devenv/state/postgres
devenv up

Issue 3: Slow shell activation

Solution:

# Use cachix for faster builds
cachix use devenv

# Or build in advance
devenv shell --build-first

Issue 4: Processes not starting

Solution:

# Check process health probes
processes.api = {
  exec = "python main.py";
  process-compose.readiness_probe = {
    http_get = {
      host = "localhost";
      port = 8000;
      path = "/health";
    };
  };
};

Issue 5: Python venv issues

Solution:

# Remove and recreate venv
rm -rf .venv
devenv shell

# Or disable venv
languages.python.venv.enable = false;

Issue 6: Node modules not installing

Solution:

# Ensure npm install is enabled
languages.javascript = {
  enable = true;
  npm.install.enable = true;
};

# Or run manually
scripts.install.exec = "npm install";

Advanced Features

Custom Modules

Create Module

# modules/my-service.nix
{ config, lib, pkgs, ... }:
with lib;
let
  cfg = config.services.my-service;
in {
  options.services.my-service = {
    enable = mkEnableOption "My Service";

    port = mkOption {
      type = types.int;
      default = 3000;
    };
  };

  config = mkIf cfg.enable {
    processes.my-service = {
      exec = "${pkgs.my-service}/bin/my-service";
      process-compose.environment.PORT = toString cfg.port;
    };
  };
}

Use Module

{
  imports = [ ./modules/my-service.nix ];

  services.my-service = {
    enable = true;
    port = 8080;
  };
}

Overlays

{ pkgs, ... }:
{
  nixpkgs.overlays = [
    (final: prev: {
      my-custom-pkg = prev.callPackage ./pkgs/my-pkg {};
    })
  ];

  packages = [ pkgs.my-custom-pkg ];
}

Conditional Configuration

{ pkgs, lib, ... }:
let
  isDarwin = pkgs.stdenv.isDarwin;
  isLinux = pkgs.stdenv.isLinux;
in {
  packages = with pkgs;
    [ git curl ]
    ++ lib.optionals isDarwin [ darwin.apple_sdk.frameworks.Security ]
    ++ lib.optionals isLinux [ systemd ];
}

Integration Examples

VSCode Integration

.vscode/settings.json

{
  "nix.enableLanguageServer": true,
  "nix.serverPath": "nixd",
  "nixEnvSelector.nixFile": "${workspaceRoot}/devenv.nix"
}

JetBrains Integration

Use the Nix IDE plugin and point it to your devenv.nix file.

CI/CD Integration

GitHub Actions

name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: cachix/install-nix-action@v22
      - uses: cachix/cachix-action@v12
        with:
          name: devenv
      - run: nix profile install nixpkgs#devenv
      - run: devenv test

GitLab CI

test:
  image: nixos/nix
  script:
    - nix profile install nixpkgs#devenv
    - devenv test

Command Reference

# Environment
devenv init              # Initialize new project
devenv shell             # Enter development shell
devenv info              # Show environment info

# Packages
devenv search <name>     # Search for packages
devenv search --detailed # Detailed search results

# Updates
devenv update            # Update inputs
devenv update nixpkgs    # Update specific input

# Processes
devenv up                # Start all processes (foreground)
devenv up -d             # Start in background
devenv up <process>      # Start specific process

# Testing
devenv test              # Run tests

# Containers
devenv container <name>  # Build container image

# Maintenance
devenv gc                # Garbage collect old environments
devenv repl              # Open Nix REPL with config

# Debugging
devenv print-dev-env     # Print shell environment

Success Metrics

Fast Setup: New developers productive in minutes
Reproducible: Same environment across all machines
Declarative: Everything in version control
Composable: Share configurations across projects
Tested: CI integration ensures quality
Documented: Clear configuration and scripts

Ready to create fast, reproducible development environments with devenv! 🚀

devenv

Installation

Details

Usage

Skill Instructions

name: devenv version: 1.0 description: Devenv Skill

Devenv Skill

Skill Overview

Core Capabilities

1. Installation & Setup

Prerequisites

Install devenv

On NixOS/home-manager

Optional: Cachix for faster builds

2. Project Initialization

Initialize New Project

Generated Files

3. Core Commands

Essential Commands

Using with direnv

4. Language Configuration

55+ Languages Supported

Python

JavaScript/Node.js

TypeScript

Rust

Go

Ruby

PHP

Java

Elixir

Haskell

Terraform/OpenTofu

Nix

5. Services Configuration

30+ Pre-configured Services

PostgreSQL

MySQL

Redis

MongoDB

Elasticsearch

RabbitMQ

Kafka

Nginx

Caddy

MinIO (S3-compatible storage)

Mailhog (Email testing)

Vault (Secrets management)

6. Process Management

Define Processes

Advanced Process Configuration

Start Processes

7. Scripts & Tasks

Define Scripts

Use Scripts

Tasks (Entertest/Entersh hooks)

8. Environment Variables

Configuration

Dotenv Support

Secret Management

9. Pre-commit Hooks

Common Hooks

Custom Hooks

Install Hooks

10. Containers & Deployment

Generate Container Image

Build Container

11. Packages & Dependencies

System Packages

Language-specific packages

12. Composition & Imports

Shared Configuration

Import in Project

Using devenv.yaml

13. Testing Integration

devenv test

Run Tests

CI Integration

Common Patterns

Pattern 1: Full-Stack Web Application