devenv 1.0: Rewrite in Rust

We have just released devenv 1.0! 🎉

This is a rewrite of the CLI to Python Rust, which brings with it many new features and improvements.

I would like to thank mightyiam for a week-long, Rust pair-programming session at Thaiger Sprint.

Note: Read the migration guide at the end of this post, as 1.0 is not entirely backwards compatible.

Why rewrite twice?

When I started to write this blog post for the Python rewrite, I came up with only excuses as to why it is not fast and realized that we were simply breaking our promise to you.

The second reason is that in the Nix community there has been a lot of controversy surrounding flakes (that's for another blog post); two years ago, the tvix developers decided to do something about it and started a rewrite of Nix in Rust. This leaves us with the opportunity in the future to use the same Rust libraries and tooling.

What's new?

There are many contributions in this release, spanning over a year, but here are some of the highlights:

process-compose is now the default process manager

devenv up is now using process-compose, as it handles dependencies between processes and provides a nice ncurses interface to view the processes and their logs.

Testing infrastructure

Testing has been a major focus of this release, and a number of features have been added to make it easier to write and run tests.

The new enterTest attribute in devenv.nix allows you to define testing logic:

{ pkgs, ... }: {
  packages = [ pkgs.ncdu ];

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

  enterTest = ''
    wait_for_port 5432
    ncdu --version | grep "ncdu 2.2"

When you run devenv test, it will run the enterTest command and report the results.

If you have any processes defined, they will be started and stopped.

Read more about this in the testing documentation.

This allows for executing tests with all of your tooling and processes running—extremely convenient for integration and functional tests.


Since nixpkgs-unstable has fairly few tests, we have created devenv-nixpkgs to run tests on top of nixpkgs-unstable—applying patches we are upstreaming to address any issues.

We run around 300 tests across different languages and processes to ensure all regressions are caught.

Non-root containers

Generated containers now run as a plain user—improving security and unlocking the ability to run software that forbids root.


Due to socket path limits, the DEVENV_RUNTIME environment variable has been introduced: pointing to $XDG_RUNTIME_DIR by default and falling back to /tmp.

First-class support for Python native libraries

This one was the hardest nut to crack.

Nix is known to provide a poor experience when using tools like pip.

A lot of work has been put in here, finally making it possible to use native libraries in Python without any extra effort:

{ pkgs, lib, ... }: {
  languages.python = {
    enable = true;
    venv.enable = true;
    venv.requirements = ''
    libraries = [ pkgs.cairo ];

CLI improvements

If you need to add an input to devenv.yaml, you can now do:

devenv inputs add <name> <url>

To update a single input:

devenv update <input>

To build any attribute in devenv.nix:

devenv build languages.rust.package

To run the environment as cleanly as possible while keeping specific variables:

devenv shell --clean EDITOR,PAGER

The default number of cores has been tweaked to 2, and max-jobs to half of the number of CPUs. It is impossible to find an ideal default, but we have found that too much parallelism hurts performance—running out of memory is a common issue.

... plus a number of other additions: 1.0.0: Fast, Declarative, Reproducible, and Composable Developer Environments

Usage: devenv [OPTIONS] <COMMAND>

  init       Scaffold devenv.yaml, devenv.nix, .gitignore and .envrc.
  shell      Activate the developer environment.
  update     Update devenv.lock from devenv.yaml inputs.
  search     Search for packages and options in nixpkgs.
  info       Print information about this developer environment.
  up         Start processes in the foreground.
  processes  Start or stop processes.
  test       Run tests.
  container  Build, copy, or run a container.
  inputs     Add an input to devenv.yaml.
  gc         Deletes previous shell generations. See
  build      Build any attribute in devenv.nix.
  version    Print the version of devenv.
  help       Print this message or the help of the given subcommand(s)

  -v, --verbose
          Enable debug log level.
  -j, --max-jobs <MAX_JOBS>
          Maximum number of Nix builds at any time. [default: 8]
  -j, --cores <CORES>
          Maximum number CPU cores being used by a single build.. [default: 2]
  -s, --system <SYSTEM>
          [default: x86_64-linux]
  -i, --impure
          Relax the hermeticity of the environment.
  -c, --clean [<CLEAN>...]
          Ignore existing environment variables when entering the shell. Pass a list of comma-separated environment variables to let through.
  -d, --nix-debugger
          Enter Nix debugger on failure.
  -n, --nix-option <NIX_OPTION> <NIX_OPTION>
          Pass additional options to nix commands, see `man nix.conf` for full list.
  -o, --override-input <OVERRIDE_INPUT> <OVERRIDE_INPUT>
          Override inputs in devenv.yaml.
  -h, --help
          Print help

Migration guide


  • devenv container --copy <name> has been renamed to devenv container copy <name>.
  • devenv container --docker-run <name> has been renamed to devenv container run <name>.
  • devenv ci has been renamed to devenv test with a broader scope.

Breaking changes

  • .env files must start with the .env prefix.
  • The need for the --impure flag has finally been removed, meaning that devenv is now fully hermetic by default.

Things like builtins.currentSystem no longer work—you will have to use pkgs.stdenv.system.

If you need to relax the hermeticity of the environment you can use devenv shell --impure.

  • Since the format of devenv.lock has changed, newly-generated lockfiles cannot be used with older versions of devenv.

Looking ahead

There are a number of features that we are looking to add in the future—please vote on the issues:

Running devenv in a container

While devenv is designed to be run on your local machine, we are looking to add support for running devenv inside a container.

Something like:

devenv shell --in-container
devenv test --in-container

This would be convenient when the environment is too complex to set up on your local machine; for example, when running two databases or when you want to run tests in a clean environment.

Generating containers with full environment

Currently, enterShell is executed only once the container has started. If we want to execute it as part of the container generation, we have to execute it inside a container to generate a layer.

macOS support for generating containers

Building containers on macOS is not currently supported, but it should be possible.

Native mapping of dependencies

Wouldn't it be cool if devenv could map language-specific dependencies to your local system? In this example, devenv should be able to determine that pillow requires pkgs.cairo:

{ pkgs, lib, ... }: {
  languages.python = {
    enable = true;
    venv.enable = true;
    venv.requirements = ''


Give devenv a try, and hop on to our discord to let us know how it goes!


devenv 0.6: Generating containers and instant shell activation

After about two months of active development, I'm happy to announce devenv 0.6 is ready.

This release comes with the most notable improvements based on the feedback from existing users:

Generating containers

While devenv shell provides a simple native developer environment experience, devenv container <name> allows you to generate and copy OCI container into a registry.

Containers are a great way to distribute ready-made applications, leveraging platforms like to deploy them into production.

An example for Ruby:

  name = "simple-ruby-app";

  languages.ruby.enable = true;
  languages.ruby.version = "3.2.1";

We can generate a container called shell that enters the environment, copy it to the local Docker daemon and run it:

$ devenv container shell --docker-run
(devenv) bash-5.2# ruby --version
ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-linux]

You can read more in the new Containers section of the documentation, specifically:

Instant shell activation

Especially monorepo developer environments can sometimes be even a few gigabytes of size, taking a few seconds for the environment to be activated.

A developer environment should only be built when something changes and if not, the environment can be used instantly using a cached snapshot.

With the latest integration, we've finally reached that goal by making caching work properly (it will even watch each of your imports for changes!).

Migrating from an older devenv

Make sure to use the latest .envrc from devenv init and for everyone on the team to upgrade to devenv 0.6.

In the near future we'll experiment to improve devenv shell experience.

Hosts and certificates

Hosts and certificates can now be specified declaratively:

{ pkgs, config, ... }:

  certificates = [

  hosts."" = "";

  services.caddy.enable = true;
  services.caddy.virtualHosts."" = {
    extraConfig = ''
      tls ${config.env.DEVENV_STATE}/mkcert/ ${config.env.DEVENV_STATE}/mkcert/
      respond "Hello, world!"

And when you run devenv up to start the processes, these hosts and certificates will be provisioned locally.

allowUnfree and overlays

For example in devenv.yaml:

allowUnfree: true
    url: github:NixOS/nixpkgs/nixpkgs-unstable
    url: github:oxalica/rust-overlay
      - default

Will allow building unfree software and wire up default overlay into pkgs from rust-overlay.

Migrating from an older devenv

Make sure everyone on the team upgrades to devenv 0.6.

Languages changelog

  • Python: Added support for virtualenv creation and poetry by bobvanderlinden.
  • Ruby: First-class support for setting version or versionFile by bobvanderlinden.
  • Go: Received significant improvements by shyim.
  • PHP: Added first-class support for setting version to make it easier to set extensions by shyim.
  • Scala: Now allows changing the package and offers scala-cli as an option if the JDK is too old by domenkozar.
  • R: Added an option to specify the package by adfaure.
  • Rust: Can now find headers for darwin frameworks by domenkozar.
  • OCaml: Allowed using a different version of OCaml by ankhers.
  • Tex Live: Added support by BurNiinTRee.
  • Swift: Added support by domenkozar.
  • Raku: Added support by 0pointerexception.
  • Gawk: Added support by 0pointerexception.
  • Racket: Added support by totoroot.
  • Dart: Added support by domenkozar.
  • Julia: Added support by domenkozar.
  • Crystal: Added support by bcardiff.
  • Unison: Added support by ereslibre.
  • Zig: Added support by ereslibre.
  • Deno: Added support by janathandion.

Services changelog

  • Cassandra: Added by ankhers.

  • CouchDB: Added by MSBarbieri.

  • MariaDB: Corrected user and database handling by jochenmanz.

  • MinIO: Now allows specifying what buckets to provision by shyim.

Fixed issues and other improvements

  • process-compose: Faster shutdown, restart on failure by default, escape env variables properly by thenonameguy.

  • Support assertions in modules by bobvanderlinden.

  • Fix overmind root by domenkozar.

  • Make devenv info output pluggable from devenv modules by domenkozar.

  • Expand the flake guide by sandydoo.

  • Set LOCALE_ARCHIVE when missing by sandydoo.

  • Numerous option documentation fixes by sandydoo.

  • Fix starship integration with a custom config by domenkozar.

  • Test direnv integration with strict bash mode by stephank.

  • Add a shim devenv for flakes integration by rgonzalez.

devenv 0.5


  • devenv search now shows results from the options that can be set in devenv.nix:

devenv search results


  • Rust language support now integrates with fenix to provide stable/nightly/unstable toolchain for cargo, rustc, rust-src, rust-fmt, rust-analyzer and clippy.

  • Python language now sets $PYTHONPATH to point to any installed packages in packages attribute.

  • Ruby langauge support now defaults to the latest version 3.1.x, ships with an example running rails, sets $GEM_HOME and $GEM_PATH environment variables. Next release will support picking any version of Ruby - please leave a thumbs up.

  • jpetrucciani contributed Nim, V and HCL/Terraform languages support.



Bug fixes

devenv 0.4


  • New command devenv info shows locked inputs, environment variables, scripts, processes and packages exposed in the environment.

  • Tracebacks are now printed with most relevent information at the bottom.

  • New option process.implementation allows you to choose how processes are run. New supported options are overmind and process-compose.

  • Instead of passing each input separately in devenv.nix, the new prefered and documented way is via inputs argument, for example inputs.pre-commit-hooks.

  • samjwillis97 contributed support for MongoDB.

  • shyim contributed MySQL/MariaDB support.

  • shyim made PHP configuration more configurable, for example you can now set extensions.

  • JanLikar improved PostgreSQL support to expose psql-devenv script for connecting to the cluster.

  • datakurre added robotframework support.

Bug fixes

  • Composing using inputs has been fixed.

  • It's now possible to use devenv on directories with spaces.

  • Update checker is no longer using environment variables to avoid some corner cases.

devenv 0.3

It has been 3 days since 0.2 release, so it's time for 0.3:


Bug fixes


devenv 0.2

After an intense weekend and lots of incoming contributions, v0.2 is out!


  • All the devenv.nix options you can define now come as an input (instead of being packaged with each devenv release). To update the options you can run devenv update and it will match devenv.nix reference.

  • New devenv search command:

$ devenv search ncdu
name         version  description
pkgs.ncdu    2.1.2    Disk usage analyzer with an ncurses interface
pkgs.ncdu_1  1.17     Disk usage analyzer with an ncurses interface
pkgs.ncdu_2  2.1.2    Disk usage analyzer with an ncurses interface

Found 3 results.
  • shyim contributed Redis support and is working on MySQL.

  • Languages: raymens contributed dotnet, ankhers contributed Elixir and Erlang support.

  • If devenv.local.nix exists it's now also loaded, allowing you to override git committed devenv.nix with local changes. Hurrah composability!

Bug fixes

  • Variables like env.DEVENV_ROOT, env.DEVENV_STATE and env.DEVENV_DOTFILE are now absolute paths paths
  • shyim fixed /dev/stderr that is in some environments not available.
  • domen fixed shell exiting on non-zero exit status code.


Hello world: devenv 0.1

After lengthy conversations at NixCon 2022 about Developer Experience and current painpoints around documentation, I've started hacking and experimenting.

The goal is to bring the strengths of Nix to the world with what we have best to offer, and I'm happy to announce:

devenv: Fast, Declarative, Reproducible, and Composable Developer Environments

Local containerless environments

One of the reasons why developer environments are moving into the cloud are the lack of good tooling how to make those environments reproducible.

In the last decade we've doubled down on shipping binary blobs in containerized environments.

Just as we went from virtual machines to containers, we can make one step further and create guarantees at the package level and treat those as a building block.

devenv 0.1 release brings the basic building blocks for many possibilities of what can be built in the future.

I invite you to explore the documentation and give it a try.


I'm looking forward in what ways the developer community uses devenv and stay tuned for roadmap updates by subscribing at our newsletter at the bottom of the page.