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.

Commands

$ devenv
https://devenv.sh 2.0.0: Fast, Declarative, Reproducible, and Composable Developer Environments

Usage: devenv [OPTIONS] [COMMAND]

Commands:
  init        Scaffold devenv.yaml, devenv.nix, and .gitignore.
  generate    Generate devenv.yaml and devenv.nix using AI
  shell       Activate the developer environment. https://devenv.sh/basics/
  update      Update devenv.lock from devenv.yaml inputs. http://devenv.sh/inputs/
  search      Search for packages and options in nixpkgs. https://devenv.sh/packages/#searching-for-a-file
  info        Print information about this developer environment.
  up          Start processes in the foreground. https://devenv.sh/processes/
  processes   Start or stop processes. https://devenv.sh/processes/
  tasks       Run tasks. https://devenv.sh/tasks/
  test        Run tests. http://devenv.sh/tests/
  container   Build, copy, or run a container. https://devenv.sh/containers/
  inputs      Add an input to devenv.yaml. https://devenv.sh/inputs/
  changelogs  Show relevant changelogs.
  repl        Launch an interactive environment for inspecting the devenv configuration.
  gc          Delete previous shell generations. See https://devenv.sh/garbage-collection
  build       Build any attribute in devenv.nix.
  eval        Evaluate any attribute in devenv.nix and return JSON.
  direnvrc    Print a direnvrc that adds devenv support to direnv. See https://devenv.sh/integrations/direnv/.
  version     Print the version of devenv.
  mcp         Launch Model Context Protocol server for AI assistants
  lsp         Start the nixd language server for devenv.nix.
  help        Print this message or the help of the given subcommand(s)

Input overrides:
      --from <FROM>
          Source for devenv.nix.

          Can be either a filesystem path (with path: prefix) or a flake input reference.

          Examples:
            --from github:cachix/devenv
            --from github:cachix/devenv?dir=examples/simple
            --from path:/absolute/path/to/project
            --from path:./relative/path

  -o, --override-input <NAME> <URI>
          Override inputs in devenv.yaml.

          Examples:
            --override-input nixpkgs github:NixOS/nixpkgs/nixos-unstable
            --override-input nixpkgs path:/path/to/local/nixpkgs

  -O, --option <OPTION:TYPE> <VALUE>
          Override configuration options with typed values.

          OPTION must include a type: <attribute>:<type>
          Supported types: string, int, float, bool, path, pkg, pkgs

          List types (pkgs) append to existing values by default.
          Add a ! suffix to replace instead: pkgs!

          Examples:
            --option languages.rust.channel:string beta
            --option services.postgres.enable:bool true
            --option languages.python.version:string 3.10
            --option packages:pkgs "ncdu git"       (appends to packages)
            --option packages:pkgs! "ncdu git"      (replaces all packages)

Nix options:
  -j, --max-jobs <MAX_JOBS>
          Maximum number of Nix builds to run concurrently.

          Defaults to 1/4 of available CPU cores (minimum 1).

          [env: DEVENV_MAX_JOBS=]

  -u, --cores <CORES>
          Number of CPU cores available to each build.

          Defaults to available cores divided by max-jobs (minimum 1).

          [env: DEVENV_CORES=]

  -s, --system <SYSTEM>
          Override the target system.

          Defaults to the host system (e.g. aarch64-darwin, x86_64-linux).

  -i, --impure
          Relax the hermeticity of the environment.

      --no-impure
          Force a hermetic environment, overriding config.

      --offline
          Disable substituters and consider all previously downloaded files up-to-date.

      --nix-option <NAME> <VALUE>
          Pass additional options to nix commands.

          These options are passed directly to Nix using the --option flag.
          See `man nix.conf` for the full list of available options.

          Examples:
            --nix-option sandbox false
            --nix-option keep-outputs true
            --nix-option system x86_64-darwin

      --nix-debugger
          Enter the Nix debugger on failure.

Shell options:
  -c, --clean [<CLEAN>...]
          Ignore existing environment variables when entering the shell. Pass a list of comma-separated environment variables to let through.

  -P, --profile <PROFILES>
          Activate one or more profiles defined in devenv.nix.

          Profiles allow you to define different configurations that can be merged with your base configuration.

          See https://devenv.sh/profiles for more information.

          Examples:
            --profile python-3.14
            --profile backend --profile fast-startup

      --reload
          Enable auto-reload when config files change (default).

      --no-reload
          Disable auto-reload when config files change.

Cache options:
      --eval-cache
          Enable caching of Nix evaluation results (default).

      --no-eval-cache
          Disable caching of Nix evaluation results.

      --refresh-eval-cache
          Force a refresh of the Nix evaluation cache.

      --refresh-task-cache
          Force a refresh of the task cache.

Secretspec options:
      --secretspec-provider <SECRETSPEC_PROVIDER>
          Override the secretspec provider

          [env: SECRETSPEC_PROVIDER=]

      --secretspec-profile <SECRETSPEC_PROFILE>
          Override the secretspec profile

          [env: SECRETSPEC_PROFILE=]

Tracing options:
      --trace-output <TRACE_OUTPUT>
          Enable tracing and set the output destination: stdout, stderr, or file:<path>. Tracing is disabled by default.

          [env: DEVENV_TRACE_OUTPUT=]

      --trace-format <TRACE_FORMAT>
          Set the trace output format. Only takes effect when tracing is enabled via --trace-output.

          Possible values:
          - full:   A verbose structured log format used for debugging
          - json:   A JSON log format used for machine consumption
          - pretty: A pretty human-readable log format used for debugging

          [env: DEVENV_TRACE_FORMAT=]
          [default: json]

Global options:
  -v, --verbose
          Enable additional debug logs.

  -q, --quiet
          Silence all logs

      --tui
          Enable the interactive terminal interface (default when interactive).

          [env: DEVENV_TUI=]

      --no-tui
          Disable the interactive terminal interface.

  -h, --help
          Print help (see a summary with '-h')

  -V, --version
          Print version information and exit

Documentation

• Getting Started
• Basics
• Roadmap
• Blog
• devenv.yaml reference
• devenv.nix reference
• Contributing