devenv.sh - Fast, Declarative, Reproducible, and Composable Developer Environments

Features

Developer experience

• Terminal UI with live build progress, task hierarchy, and error details
• Native shell reloading that rebuilds in the background while your shell stays interactive
• Instant environments with incremental Nix evaluation caching (sub 100ms when nothing changed)
• LSP for devenv.nix with autocomplete, hover docs, and go to definition via bundled nixd
• Ad hoc environments from the CLI without any config files (--option languages.rust.enable:bool true)
• Out of tree devenvs to use configs from other repos (--from github:myorg/configs)

Languages, packages, and services

• 50+ languages with built in tooling: compilers, LSP servers, formatters, linters, and version selection
• 100,000+ packages from Nixpkgs for Linux, macOS, x64, and ARM64 (including WSL2)
• 40+ services like PostgreSQL, Redis, MySQL, MongoDB, Elasticsearch, Caddy, and more

Processes and tasks

• Native process manager written in Rust with dependency ordering, restart policies, readiness probes (exec, HTTP, systemd notify), socket activation, watchdog heartbeats, and file watching
• Automatic port allocation that finds free ports so parallel environments never collide
• Tasks with DAG based execution, caching, parallel runs, and namespace support
• Scripts with access to all environment packages

Packaging and deployment

• OCI containers built from your environment without Docker
• Outputs for packaging apps using each language's best tools (crate2nix, uv2nix, ...)
• Polyrepo support to reference outputs and options across repositories

Composition and configuration

• Profiles for environment variants (--profile backend --profile testing)
• Composable via imports to share and reuse environments across projects
• Inputs for pinning and overriding Nix dependencies

Security and integrations

• SecretSpec for declarative, provider agnostic secrets management (keyring, 1Password, dotenv)
• Git hooks via git-hooks.nix with pre configured formatters and linters
• Testing with devenv test that automatically starts and stops processes
• direnv integration for automatic shell activation when entering a directory
• MCP server for AI assistant integration (package and option search)
• AI generation to scaffold environments from a natural language description

Quick start

Running devenv init generates devenv.nix:

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

{
  # https://devenv.sh/basics/
  env.GREET = "devenv";

  # https://devenv.sh/packages/
  packages = [ pkgs.git ];

  # https://devenv.sh/languages/
  # languages.rust.enable = true;

  # https://devenv.sh/processes/
  # processes.dev.exec = "${lib.getExe pkgs.watchexec} -n -- ls -la";

  # https://devenv.sh/services/
  # services.postgres.enable = true;

  # https://devenv.sh/scripts/
  scripts.hello.exec = ''
    echo hello from $GREET
  '';

  # https://devenv.sh/basics/
  enterShell = ''
    hello         # Run scripts directly
    git --version # Use packages
  '';

  # https://devenv.sh/tasks/
  # tasks = {
  #   "myproj:setup".exec = "mytool build";
  #   "devenv:enterShell".after = [ "myproj:setup" ];
  # };

  # https://devenv.sh/tests/
  enterTest = ''
    echo "Running tests"
    git --version | grep --color=auto "${pkgs.git.version}"
  '';

  # https://devenv.sh/outputs/
  # outputs = {
  #   rust-app = config.languages.rust.import ./rust-app {};
  #   python-app = config.languages.python.import ./python-app {};
  # };

  # https://devenv.sh/git-hooks/
  # git-hooks.hooks.shellcheck.enable = true;

  # See full reference at https://devenv.sh/reference/options/
}

And devenv shell activates the environment.

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