devenv - Declarative Nix Developer Environments Cheatsheet

devenv - Declarative Nix Developer Environments Cheatsheet

devenv (by Cachix) builds fast, declarative, reproducible, and composable developer environments using Nix directly. Unlike tools that hide Nix behind JSON, devenv embraces the Nix language for its config, which gives you more power and flexibility: languages, packages, services (databases, caches), long-running processes, scripts, environment variables, and pre-commit/git hooks — all defined in one devenv.nix. It is the choice when you want full Nix capability with a batteries-included, developer-friendly layer.

Installation

Method	Command
Requirement	Nix with flakes enabled
Install	nix profile install nixpkgs#devenv (or via Cachix instructions)
Cachix	recommended for fast binary caching
Verify	devenv version

Getting Started

Command	Description
devenv init	Scaffold devenv.nix + devenv.yaml
devenv shell	Enter the environment
devenv up	Start defined processes/services
devenv test	Run configured tests/checks
devenv update	Update inputs (pin newer versions)
devenv gc	Garbage-collect old environments

The Config (devenv.nix)

{ pkgs, ... }:
{
  # Packages available in the shell
  packages = [ pkgs.git pkgs.jq ];

  # Languages (managed toolchains)
  languages.javascript.enable = true;
  languages.python = {
    enable = true;
    version = "3.12";
  };

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

  # Env vars
  env.APP_ENV = "development";

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

  # Long-running processes
  processes.web.exec = "npm run dev";

  # Git hooks (pre-commit)
  pre-commit.hooks = {
    prettier.enable = true;
    ruff.enable = true;
  };
}

Key Building Blocks

Block	Purpose
packages	Arbitrary Nix packages in the shell
languages.*	First-class language support (node, python, go, rust, …)
services.*	Databases/caches (postgres, redis, mysql, mongodb, …)
processes.*	Long-running commands managed by devenv up
scripts.*	Named commands runnable in the shell
env.*	Environment variables
pre-commit.hooks.*	Git pre-commit integrations

Services & Processes

Command	Description
devenv up	Start all processes and services
devenv up -d	Start in the background
devenv processes down	Stop processes
services.postgres.enable = true;	Add a managed Postgres
services.postgres.initialDatabases	Seed databases on start

Git Hooks (pre-commit)

devenv integrates pre-commit hooks declaratively — enable a hook and it runs on commit.

Hook example	Runs
prettier.enable	Format JS/TS/etc.
ruff.enable	Lint Python
nixpkgs-fmt.enable	Format Nix
shellcheck.enable	Lint shell scripts

CI & Containers

Use	How
CI	devenv test / devenv shell -- <cmd> for identical envs
Containers	devenv container build produces OCI images
direnv	.envrc with use devenv auto-enters on cd
Flakes	Composable with the wider Nix flake ecosystem

Common Workflows

# Reproducible full-stack env: language + database + process
devenv init
# edit devenv.nix: enable python, services.postgres, processes.web
devenv shell        # tools available
devenv up           # postgres + web process running

# Build a container from the same definition
devenv container build web

devenv vs Devbox vs raw Nix

Aspect	devenv	Devbox	Nix (raw)
Config	Nix language	JSON	Nix language
Power	High (full Nix)	Medium	Highest
Services/processes	Built-in, rich	Basic services	DIY
Learning curve	Moderate (Nix)	Gentle	Steep
Best for	Powerful declarative envs	Easy reproducible envs	Total control

If Nix syntax is a barrier, Devbox offers a JSON-based alternative over the same foundation; see Nix for the base.

Resources

• Official Website
• GitHub Repository
• Documentation