devenv-setup

name: devenv-setup description: Set up and configure devenv developer environments. Use when the user wants to create a devenv.nix, add languages, services, packages, or configure a reproducible development environment.

devenv Setup

When to use

Use this skill when:

Creating a new devenv.nix configuration
Adding programming languages, services, or packages
Configuring processes, tasks, or git hooks
Setting up a reproducible developer environment

Quick start

Initialize a new project:

devenv init

This creates devenv.nix and devenv.yaml in the current directory. For installation instructions, see https://devenv.sh/getting-started/.

Configuration

devenv.nix

The main configuration file. Example:

{ pkgs, ... }:

{
  packages = [ pkgs.git pkgs.curl ];

  languages.rust.enable = true;

  services.postgres.enable = true;

  processes.server.exec = "cargo run";
}

devenv.yaml

Defines inputs and imports:

inputs:
  nixpkgs:
    url: github:cachix/devenv-nixpkgs/rolling

Key features

Languages: languages.<name>.enable = true; — supports 50+ languages
Services: services.<name>.enable = true; — supports 100+ services (postgres, redis, etc.)
Packages: packages = [ pkgs.<name> ]; — any package from nixpkgs
Processes: processes.<name>.exec = "command"; — managed background processes
Scripts: scripts.<name>.exec = "command"; — custom shell scripts
Tasks: tasks.<name>.exec = "command"; — DAG-based task execution
Git hooks: git-hooks.hooks.<name>.enable = true; — pre-commit hooks
Containers: containers."<name>" = { ... }; — OCI containers

Ad-hoc environments

Run commands in a temporary environment without creating files:

devenv -O languages.rust.enable:bool true shell
devenv -O languages.python.enable:bool true -O packages:pkgs "nodejs git" shell -- node --version

Commands

devenv shell — enter the development shell
devenv up — start all processes
devenv test — run tests
devenv build — build outputs
devenv search <query> — search for packages
devenv update — update all inputs
devenv update <name> — update a specific input

MCP server

devenv provides an MCP server with search_packages and search_options tools. Use it for looking up available packages and configuration options.

devenv mcp          # stdio mode
devenv mcp --http   # HTTP mode on port 8080

To wire it up automatically in a project, add to devenv.nix:

{
  # For Claude Code
  claude.code.mcpServers.devenv = {
    type = "stdio";
    command = "devenv";
    args = [ "mcp" ];
  };

  # For OpenCode
  opencode.mcp.devenv = {
    type = "local";
    command = [ "devenv" "mcp" ];
  };
}

A hosted instance is also available at https://mcp.devenv.sh.