Configuring Devenv

Devenv Configuration

Initializes, configures, and searches devenv development environments.

Your Task

Determine action from $ARGUMENTS or context:

Progress Checklist

• Determine action (init/config/search)
• Check current state
• Execute action
• Validate changes
• Guide next steps

Initializing Projects

Step 1: Check Prerequisites

# Check if devenv exists
test -f devenv.nix && echo "exists" || echo "new"

# Check if devenv is installed
devenv version

If not installed: curl -L https://get.devenv.sh | sh

Step 2: Detect Project Type

Step 3: Create Configuration

Python:

{ pkgs, ... }:

{
  languages.python = {
    enable = true;
    version = "3.11";
    venv.enable = true;
  };

  scripts = {
    test.exec = "pytest";
    lint.exec = "ruff check .";
  };

  git-hooks.hooks = {
    black.enable = true;
    ruff.enable = true;
  };
}

Node.js:

{ pkgs, ... }:

{
  languages.javascript = {
    enable = true;
    npm.enable = true;  # or bun.enable
  };

  scripts = {
    dev.exec = "npm run dev";
    test.exec = "npm test";
  };

  git-hooks.hooks = {
    prettier.enable = true;
    eslint.enable = true;
  };
}

Rust:

{ pkgs, ... }:

{
  languages.rust.enable = true;

  packages = with pkgs; [ cargo-watch ];

  scripts = {
    dev.exec = "cargo watch -x run";
    test.exec = "cargo test";
  };

  git-hooks.hooks = {
    rustfmt.enable = true;
    clippy.enable = true;
  };
}

Go:

{ pkgs, ... }:

{
  languages.go.enable = true;

  packages = with pkgs; [ golangci-lint air ];

  scripts = {
    dev.exec = "air";
    test.exec = "go test ./...";
  };

  git-hooks.hooks = {
    gofmt.enable = true;
    govet.enable = true;
  };
}

Step 4: Create Supporting Files

.envrc:

use devenv

.gitignore additions:

.devenv*
devenv.lock
.direnv

Step 5: Validate

nix-instantiate --parse devenv.nix
devenv info
direnv allow

Configuring Projects

Always Read First

cat devenv.nix

Languages

languages = {
  javascript = {
    enable = true;
    npm.enable = true;      # or bun.enable, pnpm.enable
  };
  python = {
    enable = true;
    version = "3.11";
    venv.enable = true;
  };
  rust.enable = true;
  go.enable = true;
};

Packages

packages = with pkgs; [
  gh            # GitHub CLI
  jq            # JSON processor
  docker
  kubectl
];

Scripts

scripts = {
  dev.exec = "npm run dev";
  test.exec = "pytest tests/";
  db-reset.exec = ''
    dropdb myapp --if-exists
    createdb myapp
  '';
};

Git Hooks

git-hooks.hooks = {
  prettier.enable = true;
  eslint.enable = true;
  black.enable = true;
  rustfmt.enable = true;
  shellcheck.enable = true;
  gitleaks.enable = true;
};

Services

services = {
  postgres = {
    enable = true;
    initialDatabases = [{ name = "myapp_dev"; }];
  };
  redis.enable = true;
  mysql.enable = true;
};

Processes

processes = {
  backend.exec = "uvicorn main:app --reload";
  frontend.exec = "npm run dev";
};

Start all with devenv up.

Environment Variables

env = {
  DATABASE_URL = "postgresql://localhost/myapp";
  API_KEY = "dev-key";
};

Validation After Changes

nix-instantiate --parse devenv.nix
devenv info
direnv reload

Searching Packages/Options

Using CLI

devenv search <query>

Using MCP Tools

Use mcp__mcp_devenv_sh__search_packages and mcp__mcp_devenv_sh__search_options.

Common Corrections

Present Results

## Search Results for "{query}"

### Configuration Options
| Option | Description |
|--------|-------------|
| `languages.python.enable` | Enable Python support |

### Packages
| Package | Description |
|---------|-------------|
| `python311` | Python 3.11 interpreter |

### Usage Example
(show nix snippet)

Full-Stack Configuration

For frontend + backend + database:

{ pkgs, ... }:

{
  languages = {
    javascript = {
      enable = true;
      npm.enable = true;
    };
    python = {
      enable = true;
      version = "3.11";
      venv.enable = true;
    };
  };

  env = {
    DATABASE_URL = "postgresql://localhost:5432/myapp_dev";
    API_URL = "http://localhost:8000";
  };

  services.postgres = {
    enable = true;
    initialDatabases = [{ name = "myapp_dev"; }];
  };

  processes = {
    backend = {
      exec = "cd backend && uvicorn main:app --reload --port 8000";
      process-compose = {
        depends_on.postgres.condition = "process_healthy";
      };
    };
    frontend = {
      exec = "cd frontend && npm run dev";
      process-compose = {
        depends_on.backend.condition = "process_healthy";
      };
    };
  };

  scripts = {
    dev.exec = "devenv up";
    db-reset.exec = ''
      dropdb myapp_dev --if-exists
      createdb myapp_dev
    '';
  };

  git-hooks.hooks = {
    prettier.enable = true;
    black.enable = true;
  };
}

Error Handling

Tips

• Always read devenv.nix before editing
• Use MCP search tools to find correct names
• Prefer languages.* over adding interpreter packages
• Use services.* for databases (auto-configured)
• Use processes for multi-service development
• Test changes with devenv info after editing
• Scripts become shell commands automatically