devenv - The best tool for the job

2025-12-12 devenv, dev tools, productivity

I cannot recall when I discovered devenv; it's been at least a year at this point. devenv offers "fast, declarative, reproducible, and composable developer environments" which undersells how useful the service is for developers.

With devenv I have a single place to:

Declare external dependencies to packages in the massive NixOS Package Manager
Manage precommit hooks
Set up services like a database and redis
Centralize environment variables
Maintain scripts and tasks for common actions

Whenever I make a change to my devenv.nix, my isolated environment, powered by Nix, is immediately updated to match the desired state I declared in the file. For teams, all someone has to do is set up devenv then cd into the project directory which immediately triggers installation of all necessary packages.

No more arguments needed about Makefile vs. Justfile. No more maintaining docker compose files just to run a database and redis for development. Installation instructions are typically neglected until the next unfortunate soul onboards to discover just how bad the situation is. If you are lucky, they decide to update it for you. With devenv, that problem is pretty much gone. Every project has its own configuration that is isolated to that area of the filesystem. When I leave the directory, the environment is gone - the dependencies are not polluting my global environment. I don't even need nvm or pipenv or mise or asdf (although mise and asdf are great!) anymore as devenv already handles language version management too.

Check out this snippet of a devenv.nix file from one of my projects. It sets up a database, a reverse proxy so I can test locally with HTTPS, Redis, and more. And I know I have barely scratched the surface of what I can do with devenv.

There are ways to build OCI Containers from your configuration. Profiles, Overlays, and even setup to to manage Claude Code with devenv!

However, I do want to call out that my difficulties when testing in GitHub Actions. Setting up devenv is painfully slow. The company who built the service, cachix, is a provider of binary caching services that are meant to speed things up when deploying the same environment in different places, which I think is what I have to do for CI.

I do not want to pay the $X/mo. for that service right now, so my CI setup is woefully archaic. Shoutout to turborepo for simplifying that step!

If you are tired of juggling tools and dependencies, then hopefully this sells you on one of the last tools you really, truly need.